Tobacco Documents Online

Chromosome Translocations and Human Cancer Chromosomes in a cell of the immune system sometimes "trade" segments ofDNA. T'his process can activate cancer-cacrsing genes 6y placing them neargenetic sequences that enhance their acti vity vt ry human cell contains ont:o- E genes, genes that have the poten- tial to cause cancer. These genes apparently carry out normal functions until a malignant change takes place. What is it that changes the oncogene from a normal part of the cell's genetic machinery into a source of cancerous, or neoplastic, transformationT. In the past decade several different mechanisms by which an oncogene may be activated have been discovered (aee "A Molecular Basis of Cancer," by Robert A. Weinberg; Scttxrunc AmEtuc,w, November, 1983). Some- times an oncogene is activated by a "point mutation"; a small segment of the gene is altered' by radiation or a chemical carcinogen. Another, way an oncogene can be activated is through °amplification," in which the oncogene is somehow replicated many times so that several active copies of it are pres- ent in the same cell. When this hap- pens, the gene may be expressed at an inappropriately high level; in other words, the cell may make too much of the protein encoded by the gene. Even a protein that is necessary for the prop- er functioning of the cell' may have cancerous effects when it is produced in large quantities (see "The Proteins of Oncogenes," by'Tony Hunter; Set- Fxtitic Ata>attcA>v, August, 198dJ. An oncogene could also be activat- ed by incorporation into a retrovirus (a virus whose genetic material is made of RNA rather than DNA). When a retrovirus infects an animal cell, it un pick up from the cell an unactivated oncogene, which becomes part of the genetic complement of the retrovirus and its progeny. This process some- times activates the oncogene, and so subsequent infection by that strain of retroviTus can induce a neoplastic transformation in a different cell. At present it is not clear wtuC role these 54 by Carlo M. Croce and George Klein mechanisms of activation play in the development of human tttmors, since few human tumors carry an oncogene activated in any of these ways. Our work and the work of other in- vestigators has shown there is yet an- other mechanism that can activate an oacogene. This mechanism operates in some cancers of cells in the immune system called B, cells. The primary function of a B cell is to produce anti- bodies (immtmoglobulins), the mole- cules that recognize and bind to the "nonself," or foreign, molecules called antigens. The genes that encode the production of antibodies must be ex- pressed at a high level for the B cell to fulfill its function properly. Genetic se- quences within the genes that encode antibody production increase the ac- tivity of such genes in B cells. If a re- arrangement of the B cell's chromo- somes (rodlike strands of DNA that contain the cell's genes) somehow jux- taposed such a sequence with an onco- gene, then expression of the oncogene would be enhanced. Malignant trans- formation would seemingly become a primary part of that cell's function. We have found that such rearrange- ments do indeed occur in Burkitt's lymphoma, an extremely fast-grow- ing malignancy of the immune system. The rearrangements result from recip- rocal translocations between two of the B cell's chromosomes: a segment of each chromosome breaks off and moves to the end of the other chromo- some [scr lllusnation on page 36]. In most of these translocations an onco- gene moves into a position near one of the sequences that enhances antibody production; less often the oncogene re- mains in place and the enhancing se- quence shifts. We came on this mechanism in the course of research begun in the late 1970's to identify, the chromosomes that contain the genes responsible for antibody production. Once we had mapped the locations of these genes, we noticed they lay on precisely the same chromosomes that were already known to be yianslooated in Burkitt's lymphoma cells. Our later reaearch showed that the two segments of genet- ic material that translocate between chromosomes contain, respectively; an oncogene and a gene encoding part of the antibody molecule.. r In order to discover which chromo- somes contain the genetic infor- mation that codes for antibody pro- duction, one of us (Croce) and his associates employed an experimental technique involving hybrids between mouse and' human somatic cells (body cells rather than eggs or sperm). Hybrid cells are produced' by mixing mouse and human B cells in a medi- ttm containing a chemical' or viral fu- sion factor, which joins some mouse and human cells. The resulting hybrids contain both human and mouse chro- mosomes. Each hybrid cell of this type may lose some human chromosomes during cell division (although it retains its entire complement of mouse chro- mosomes), and so as the cells divide and multiply successive generations have fewer human chromosomes; af- ter many generations each of the hy- brid cells will have only a few human chromosomes. To determine which chromosomes hold the genes coding for parts of the antibody molecule, we examined sev- eral panels of such cells. Any cell pro- ducing a part of the molecule must have contained one of the necessary chromosomes. We were able to deter- mine which chromosomes hold the genes for any particular part, of the antibody molecule by noting which human chromosomes were always N 0 ~ CJ ~

) 'present in cells producing that part but absent in any cells not producing it. The antibody molecule is made up of four protein chains; the chains link in two identical pairs to form a Y shape [aoe ill4srrarion on page 37]. The longer chain in each pair is called the heavy chain, and the shorter one is called the light chain. Each chain con- sists of two characteristic regions: the "variable" region and the "constant"' region. The variable region recognizes and binds to antigens; the constant re- gion specifies the task to be performed by the antibody (called its effector function)', after it has encountered and bound an antigen. There are many dif- In 1979 one of us (Croce) and' his associates found that hybrid cells con. taining human chromosome 14 were the only ones to produce human heavy chains. Apparently the genes coding for production of heavy chains lie on chromosome 14. Using similar ex- perimental techniques Jan Erikson, Joanne Martinis and one o[ us (Croce) found in 1981 that chromosome 22 encodes the light chains bearing the lambda constant region. In 1982 O. Wesley McBride and his associates at the National Cancer Institute and Ter- ence H. Rabbitts and his collaborators at the Medical Research Council's Laboratory of Molecular Biology in . , t i . e+ ! ,,. , ~ • , . ~ ..:~* a ferent types of variable region, be- cause antibodies are highly selective: each binds to only one specific anti- gen. In contrast, only two types of constant region occur in light chains (called kappa and lambda respective- ly) and only 10 types of constant re- gion occur in heavy chains. Thus anti- bodies to different antigens may well perform the same task. Each mature B cell can produce only one type of anti- body, and the cell's chromosomes con- tain DNA coding for the variable and constant regions specific to that anti- body [see "The Genetics of Antibody Diversity: • by Philip Leder; Saixxt'tFtt: As.tetur.iuv, May, 1982). ;i , .• r~ +~ Lw A ~ • , r O ., _•.~. CHItOM©3OKU from a Yrbrid of mome aad aaaun cel4 i.- ctude humae (peJt) and mome (dark) chromo.omea 0.e of the t»- maa clromasomm (arror-) 5ac usd ersoae a tsamlocatlos: a.aYmest or one ted t,as broken oQ .ad' bas been replaced by a aelmeat tros another chromosome. 'rranslocat{oas caa acti.ate o.coaeas (sess that nme eaecer) by placing tt.e. •ear eaea.cen, seaetle w que.eem that Iacrea.e actlrity .t eertais other aess oa the nmt I` cbrommoae. Dec.me hybrid cetin Qo.taf..ome, Mt.ot at4 of 6e Yama" seaettc eospkme.t, they eam be med to determi.e the chra mosomen encoding abomau prodoct: aay hamaa product prod.ced by a edl eo.talelea jrsCo.e \amas cAromosome smt be prod.ced by that cire.o.ome'lle aattwn med such hybrid cdY to Mertlfy the ckromoeoms e.ataid.= cerhfl o.coaess .ad to et.da the d- Iecri of .arios ttamloeatloar on t!e regulatlon of tt.e.e o.coae.a

) Cambridge found that chromosome 2 encodes the light chains carrying the kappa coostant regiom Theae results fitted neatly with.rttrk that had been done a decade ear- lier on chromosome translocations. In 1972 George Manolov and Yanka Manolova, working at the University of Lund in Sweden, found an irregular- ity in the chromosomes of many cells that were affected' by malignant Burk- ia's lymphoma: one of the chromo- somes in the 14th pair (a human so- matic cell has 23 distinct pairs of chro- mosomes) was elongated. Noting that one section of the chromosome, called the q arm, was abnormally long, the Manolovs called the unusual chromo- some 14q+. Subsequently Lore Zech, in collabo- ration with one of us (Klein) at the Ka- rolinska institute, found that the 14q+ chromosome is the result of a recipro- cal translocation: it forms when an end segment of a chromosome in the P ARM CARM CAiOaAO®oalE e 0 © Nr eighth pair breaks off and joins chro- mosome 14. A segment of chromo- some 14 makes the opposite transition and joins the end of chromosome 8. The rearranged eighth chromosome is called 8q-, because it has a foreshort- ened q arm. More recently other work- ers found that two other chromosome translocations may occur in Burkitt's lymphoma cells. Both involve chro- mosome 8; in one kind of translocation (occurring in approximately 16 per- cent of the cases of Burkitt's lympho- ma) the reciprocal shift is between chromosomes 8 and 22. In approxi- mately 9 percent of the cases the trans- location involves chromosomes 2 and 8. Three of the chromosomes affected by these traaslocations, chromosomes 2, 14 and 22, are involved in the pro- duction of antibodies. The association between Burkitt's lymphoma and antibody production soon proved to be closer. One of us (Croce) and Erikson at the Wistar In- stitute of Anatomy and Biology and E~ C) © i= CQ F= © o aQ= NORMAL Sq- p/RO1+1O8QME a CMROMOSONff 0 0 © U 0 0 0 U I B U NORMAL t4q ' CHRO6AOSOME 14 D1HObAO''OME RECIPROCAL TRANSLOCATION Detwees clromowmes t(rad) a" 14 (trum) eaeses moat Iasta.ces of aarldtt•c tymphoma, a maL{aeascy o[ B cells is the Sumaa immme q!s- tem. A segmeat from tae e.a of chromosome i brealts off (a) a.d movs to chromosome 14 (!k T!e reverse traacbcatioa m.rs a eagme.t from chromosome 14 to chromosome g. B>ach reeiprocy er.aalootioa Vbct a. o.eoaene from chromosome a.ear a aeae on elrs masome 14:tlat asaatly eodm for productioa of pnt of t!e antibody motecole. A mecka.- iam that eahaaees rroduetton of a.ttsadis ts aoemat B eetts the. actl.atee the o.cosese. i5 JanetFinan and Peter C. Nowell of the University of Pennsylvania School of Medicine found that the point at which chromosome 14 breaks during the translocation .rith chromosome 8 is situated precisely within the section of chromosome 14 that encodes the im- munogiobulin heavy chain. For these experiments we once again used hy- brids between mouse and human cells; in this case we used cells from the mouse immune system that had been uansfotvted by a type of cancer called a plasmacytoma. Each hybrid cell con- tained, in addition to the mouse genet- ic complement, at least one chromo- some from a human Burkitt's lympho- ma ceU. As we had expected, hybrid cells with the normal chromosome 14: (the chromosome of the 14th pa'tr that had not been affected by the translocation)) possessed genes for antibody produc- tion; those with the normal chromo- some 8 did not [ice !!lusrrarion on page 191. On the other hand, hybrids with a chromosome 14 that had been in- volved in a translocation (the 14q• chromosome) contained the genes for the constant regions of heavy chains but not for the variable regions. Chro- moaome 8 that had taken part in the translocation contained the genes for the variable regions. These results are evidence that chromosome 14 breaks between the genes coding for the vari• able and constant regions of the heavy chain, and that the genes coding for the' variable region move to chromosome 8. The heavy-chain locus (the part of chromosome 14 that encodes the heavy chain) is thus directly involved in one of the translocations that is characteristic of Burkitt's lymphoma. A this point it was clear the mecha- nism of Burkitt's lymphoma was somehow related to the genes that code for the production of antibodies; our next clues to the nature of the rela- tion carne from studies of oncogenes. Because Burkitt's lymphoma affects, the B cells, we were particularly inter- ested in an oncogene designated c-myc. a human oncogene closely related to the oncogene v-myc, which causes a B- cell lymphoma in chickens that have been infected with avian myelocyta matosis virus. In collaboration with Riccardo Dal- la-Favera and Robert C. Gallo of: the National Caneer Institute, we used the close relation between human and avi- an myc genes to construct a probe that would identify hybrid cells containing the human c-myc oncogenc. Our probe was a radioactively labeled segment of human DNA whose genetic sequence was very similar to that of the v-myc oncogene.

) I > I To tell whether a hybrid cell con- tained the human c-mXc gene, we used an enzyme to cut the cell's genetic ma- terial into small segments; we then separated the segments by sise, using a process called gel electrophoresis. Next we exposed the DNA to a so- lution containing radioactive probe DNA. Both the cellular DNA and the probe had been "denatured"; that is, in each case the two complementary strand's of DNA that make up that molecule's double-helix shape had been separated. Because the o-myc probe and the human e-myc gene are nearly identical, the libekd strands of probe c-myc "hybridized" with the cel- lular c-myc: that is, single strands of probe DNA joined to complementary strands of cellular DNA. When we washed away the solution of probe DNA, any probe that had hybridized was left behind. After this washing process any cell whose genetic materi- al had hybridized with the radioactive probe could be discerned by a specific radioactive band that appeared on the filter paper holding the sorted DNA. We used the probe to examine a pan- el'. of mouse-human hybrid cells in or- der to determine the chromosotnal lo- cation of the human c-my!r gene. We first examined hybrid cells with nor- mal human chromosomes and found that human chromosome 8 was pres- ent in all cells containing the human c-myc oncogene and absent in those without it; we concluded that the c-ma+c oncogene lies on chromosome 8. Next we examined hybrid cells that contained the translocated chromo- somes 8 and 14, derived from unions between mouse cells and human Burk- itt's lymphoma cells. We observed that the c-myconcogene resides in the small uarnent of chromosome 8 that consis- tentty translocates to chromosome 14 in Burkitt's lymphoma cells containing the translocation between chromo- somes 8 and 14. This result indicated that translocations involving the e-myc oncogene play a fundamental role in development of Burkitt's lymphoma. Interestingly, similar specific ehro- mosomal translocations have afso been observed in mouse plasmacyto- mas by Shinsuke Ohno, Francis Wie- ner and Jack Spira, working at the Karolinska Institute with one of us (Klein) in collaboration with Michael Potter and his associates at the Na- tional Cancer Institute. Their study found that malignant antibody-pro- ducing cells of mice carried a charac- teristic translocation between chromo- some 15 and the mouse t:hromosomes that have either the heavy-chain genes or the genes for the light-chain kappa region (mouse chromosomes 12 and 6 respectively). Thcse results suggest A1VTiSODY MOLECULL ea.das eI two Ye.tleal g.ks .f geot.ir eWs jstad te tero a sflit V' at+ap. la ..ei pi tasre are a iaa.y claL aa4 a liNt eYda, a.i .aeb eWe ks a.attalle eegior ar4 a eosu.t eegloa. Moa eaw .t Iiaetdtt's b.phora are em.i by a traa.loeatJe..[ as e.co{e.a to 1\e ge.eek toer ..cealag the r.a.y etnh. fMha esa.r arn ea.wi by traasbeaqos iiv.l+tag g..Y tK 1!e llgit-eYia coastaa eegio.a ed that immunoglobulin genes have a role in mouse plasmacytomas. Lter experiments done by one of us (Croce), Dalla-Favera and Gallo, in collaboration with Stuart A. Aaron- son of the National Cancer Institute and Philip Leder of the Harvard Medi- cal School, showed that the c-myc on- cogene translocated to chromosome 14 in human Burkitt's lymphoma may be arranged in several ways. The oncogent consists of three ex- ons (DNA segments that are tran- scribed to make messenger RNA, or mRNA, during the process of eitpres- sion as proteins) broken up by two in- trons (segments consisting of DNA that is not transcribed into mRNA and is thus not expressed as protein). The structure of the oncogene was analyzed by Dalla-Favera and Gallo and their associates and by Rosemary Watt. Giovanni Rovera and one of us (C?o- ce) at the Wistar Institute. In some Burkitt's lymphoma translocations the breaking point on chromosome 8 is "upstream" of the entire c-myc onco- gene and all three exons of the gene are translocated to chromosome 14; in other cases, however, the breaking point is •'downstream"'of the first exon and only the second and third exons are translocated [m Jllusrrerion m page 60]. In this case the oncogene is attached "head to head"' with one of the heavy-chain genes on chromosome 14; that is, the translocated segment of DNA from chromosome 8 runs in a direction opposite to that of the DNA from chromosome 14. Other experiments have shown that a similar rearrangement occurs in translocations underlying mouse plas- macytomas. These studies were first carried out by Michael D. Cole and his associates at the St. Louis Uni- versity Medical Center, and later by Leder, by one of us (Croce) in col- laboration with Kenneth B. Marcu of the State University of New York at Stony Brook and by Jerry Adams and Suzanne Cory of the Walter and Eliza Hall Institute of Medical Research in Melbourne. In mouse plasmacytomas the c-myc oncogene is rearranged head to head with an immunoglobutin heavy-chain gene. It is not yet clear, however, whether the oncogene is tranzlocated to the heavy-chain locus or whether it remains on mouse chro- mosome 15 while the heavy-citain lo- cus is translocated near it. Iin spite of the several possible chro- mosome rearratt8ements in cells of human Burkitt's lymphoma, we found that the protein produced by the c-mrc gene was qualitatively the same. Spe- cifically we found that •the first c-myc exon does not code for a protein; pro- tein synthesis begins at the second' exon. Therefore it was not the rear- rangements of the c-myr gene during translocation that had activated its on- cogenic qualities; the cancerous effect of translocation is not due to some al- teration within the gene. If the c-myc product is the same in 57 r

normal cells and in Burkitt's lym- phoma cells, what is the oncogen- ic consequence of the chromosome translocation in Burkitt's lymphoma7 Perhaps the translocation somehow causes the tmyc gene product, small quantities of which may be necessary for the cell's fuaction, to be expressed at abnormally high levels. In other words, it is possible the translocation enables the c-myc gene to evade the methanisms that normally control its expression. If this is the ease, there should be a di5erlnce be- tween the levels of expression of the translocated gene and the normal c- myc oncogene in the same cell. Cells with the 14q• chromosome should have elevated levels of c-nqr mRNA, the genetic material that represents an intermediate step between the pres- ence of a gene on a chromosome and its expression as a protein. Cells with- normal chromosome 8 should have low levels of c~myrc mRNA. W tth that possibility in mind Kazu- ko Nishikura and our associates at the Wistar Institute undertook fur- ther experiments with hybrids of hu- man cells and mouse plasrnacytomas.. Using a method that enabled us to dis- tinguish human c-mXr mRNA trans- cripts from mouse c-mrc mRNA, we found that the c-myc gene on the 14q• chromosome is expressed at high levels; the c-reyc gene on normal ehromosome 8 is relatively sikntin the same kind of plasmacytouoa ceII. In parallel experiments we intro- duced a e-+eyc gene on normal chro- mosome 8 into mouse plasmacytoma cells. The gene had' come from non- cancerous human B ceAs. We found that this gene, which had been ex- pressed (albeit at low levels) in normal' human B cells, was shut off completely in mouse plasmacytoma cells. Adams and Cory found in other studies that the untranslocated mouse c-myc gene in mouse plastnacytoma cells ianot ex- pressed. Thus whereas the normal (un- translocated) o-myrgene is reptestxd' in the background of a mouse platanacy- toma cell, a c-myc oncogene that is translocated to the heavy-chain locus on chromosome 14 somehow escapes the mechanisms that normally controll transcription. We also examined c-myc mRNA transcripts from Burkitt's lymphoma cells carrying a variant tratuJocation. In these cells the first exon of the c-myc gene remains on chromosome 8 and the other two exons are re.rranged head to head with the genes on chro- mosome 14. (Each of these cells had a normal eighth chromosome in addi- tion to the translocated chromosome.) In these cases it is relatively easy to tell the difference between mRNA of the translocated gene and that of the gene :~ ~) It 1141 Y~ 11i it 1~ tt as cw . t4cl. M h A 11 TRANSLOCATED CHROMOSOMES of . EurkHt3 tympeow cell dttiet is NesaN trom their oatraaslocsted coaaterpatts. la tt+fs cell oae of the cdromosomes 1s t!e e!=fta pyfr tus ..deraoae a tr.nslootlos witb a chromosome from the 14th patr. The truittotat- ad earomoaome a h.s bew atroetesed oad the traostocated et.romowme 14 te.gtbead. from normal chromosome 8: the trans- located gene has been partially re- arranged and hence its mRNA tran- scripts will be different. In such cells Abbas ar-Rushdi'and our other collab- ontcrsobsetved high levels of mRNA from the translocated o-m,1r gene but not from the normal c-myc gent. Yltese results indicate the c-myc on- cogena becomes deregulated as a re- sult of proximity to genes that code for antibodies. This conclusion is strength- ened by observations concerning two translocatiotts occurring in Burkitt's lymphoma that do not involve chro- mosome 14. One of tltese transloca- tions is between chromosome 8 and tfirotnosome 22, the chromosome that contains genes encoding light chains of the lambda type. The other is between chromosome 8 and chromosome 2, the chromosome that contains genes encoding kappa light chains. In, both of these transiocations, as one of us (Croce) showed, in collaboration with Nowell and with Gilbert Lenoir of the International Agencyfior Research on Cancer in Lyons,,the c-myc gene re- mains on chromosome 8, where it is joined by a sequence that encodes anti- body production (in one case by the lambda light-ehain locus and in the other by the kappa locus). Either trans- location can activate the oncogene by making it unresponsive to the mecha- nisms that normally control expres- sion. Apparently the c-myc oncogene does not have to move in order for it to be expressed at elevated levels. What is responsible for the deregu- lation of the c-myc oncogene tak- ing part in these translocations? An ex- peritnental' observation suggests an an- swer: the translocated c-myc oncogene of Burkitt's lytnphoma is repressed in hybrid cells that are based on mouse 6lbrobl'asts (cells of connective tissue), whereas it is expressed at high levels in hybrids based on plasmacytoma cells (mal*tattt antibody-producing cr)is). It appears the translocation has an on- cogenic effect only in a cell that pro- dttas antibodies, one in which the ehromosomal regions that are neces- sary for antibody production are par- ticularly active. Such chromosomal regions contain a type of genetic sequence called an enhancer. Enhancers are sequences of DNA that seem to increase the levels of transcription of: certain other: genes on the same chromosome; they are a recent discovery and little is known about how they function. Workers in the laboratories of Kathryn L. Calame of the University of ~ California at Los Angeles, of Walter Shaffner of the University of Zurich~ and' of' Susumu 53

Tonegawa of the Massachusetts Insti- tute of Technology have found there are enhancing sequences within the segment of DNA that codes for one type of immunoglobulin heavy-chain constant region. Recent studies at the Wistar Institute suggest the presence of additional enhancers in the heavy- chain locus. In addition David Balti- more and his associates at M.I.T. have found enhancing sequences within the chromosomal regions encoding the light-chain kappa constant region. These findings suggest a possible mechanism for Burkitt's lymphoma: chromosome transi'ocationa within a B ceU place a c-myc oncogene in juxta- position to enhancers; the enhancers are capable of activating transcription over considerable distances. The c-nryc gene is then expressed' in the same way that immunoglobulin genes are ex- pressed in a normal' B cell. lnn sense the expression of the c-myc oncogene becomes a part of the cell's specialized function. ~ecent results indicate this mecha- 1~ nism of oncogettesis may be re- sponsible for many other malignancies involving cells of the human immune system. Jorge J. Yunis of the Universi- ty of Minnesota Medical School has developed a new method of banding, or staining, chromosomes that makes possible a highly precise detection of specific chromosomal changes in ma- lignant cells. His applications of this technique suggest definite ehromoso- mal changes mark the majority of B- cell malignancies. Translocations be- tween chromosome 14 and segments of either chromosome I 1 or chromo- some 18 are common in B-cell lym- phomas in adults, in human chronic B- :• y:.3 in multiple myel'o- ma. This observation, combined with our knowledge of the role of the im- munoglobulin heavy-chain locus on chromosome 14 in Burkitt's lympho- ma, indicates human oncogenes may lie on chromosomes 11 and 18; this conjecture is supported by work done by Yoshihide Tsujunoto at the Wistar Institute in collaboration with Yunis and Nowell. We have found that the breaking points in these translocations were consistently clustered in short segments of chromosome I1 or 18; in addition the breaking points always lie in front of the segment of chromo- some 14 that encodes the constant re- gion of the heavy chain. We have pro- posed ttte designations bcl-1 and bc!-2 (B-cel: lymphoma/leukemia I and 2) for the two putative oncogenes on chromosomes 11 and 18. Observations made in the study of Burkitt's lymphoma open two new major areas for investigation. First, there is the matter of enhancers. What are the precise sequences of DNA that make up an enhancer, and how does the enhancer increase the level of transcription of certain genes? The other area opened for investigation concerns the c-myr oncogene. What u the function of the c-nqrr gene in a normal cell, and why should the ex- pression of e-eryc at elevated levels cause malignancy? In addition to these new areas of re- search, our work suggests new experi- mental approaches to the study of B- cell neoplasms. Many of these malig- nancies involve the translocation of an HUMAN BURKflTS LYMPHOMA CErl NYBRID tEttS unknown oncogene to the heavy-chain locus on chromosome 14. The heavy- c?tain locus is relatively well known, and there are nucleic acid probes that make it possible for an investigator to study segments of DNA close to it. Since translocations tend to bring the otlcogene into close proximity with the heavythain locus, such probes will provide investigators with the tools to identify, isolate and characterize genes connected with the majority of human , bcelil cancers. In this way knowledge of the genetics of antibody production would yield knowledge of the genetic structure of newly isolated oncogenes. Work with chromosome vansloca- IFt1SbN FAC1oR MOUSE PtA56A/1CYTt7/AA CEU 1 fREA1CIN6' lOIiVT an tra.etoaatt.g chromosome 14 tle...kW the regio: that eac.ir the a.tlbody heavy cWa, r Ws est.eine.t.howet Ah..a. Durtittl lyspWom+e ed, c..taint.a !Wh aor.at ad tnrfscated caro.e.o.. a a.d 14, wr r.ee4 with a r.~. ptae.acrt..a eetl (a wceeo.s celt .f the .o.ee temoe syae.)6 Each hybrid ceY ef tal.d e.e af the ctrroeoaoem from the h.aaa ce4 Hybrid celr coaai.iq .ora.d clro- .oeoee a( i./), grod.ced .e a.tlbody. Calls wlta .ora.ai chromosome 14 (peax) trod.ced. the astlbody \dq ctr.h. 'lle chromosome 14 i..otrd in the traaetoeatlou co.tai.d aeas toe orty the cooetut regloar of the ba+y cital.., .ad the ta.ot.d chromosome I co.tal.ed aes tar the bea.y-cL.L .arialNe redca Appvestb ta the pocan a[ tr.rts eatba chromosome 14 brealu dir.ctb tsstweem locd e.codiq co.etaat ad +ari.6le r.ab..

tions may also lead to new methods of diagnosing and characoeri=ing cancers of the immune system. The chromoso- mal breaking points, for example, clus- ter within short segments of DNA in B-cell' malignancies that exhibit the translocations between chromosomes 11 and 14 or between chromosomes 14 and 18. It should therefore be possible to develop DNA probes that are spe- cific to these small segments. A tissue sample could, then be taken from the affected area of a patient, and the DNA probes could be used to deter- mine precisely which kind of chromo- E lAANSIOCATED GMIOMOSOMES a b E t:AYC ONCOGENE CHROMOSOME w pHi#OtAOSOME 14 CMROMOSOrtAE ti VARIETy OF TRANSLOCA77ONS na oa.e Evkkt's tympt+o- ma In the eommo.est ese (a) aD three e=om (seqoewces or DNA th.t may e.eode rroteies) of the c-reyc o.cogeee .o.e from tiro- mosome a to a secttoa e( elpomoeome 14 that le .dlace.t to the ges e.codloN tbe coastaat regioa of the astibody Ee.ry dain Ahera.Hvety (a1, chromosome a eaa break at the irst btros (ses- me.t of ".o.seese" DNA, wt,lcb in mot tra.roibed bto m1tNIA) somal rearrangement is responsible for the malignancy. Very recent results indicate that the leasons learned from B-cell malignan- cies may also be applicable to malig- nancies of Tcxlls, the other major con- stituent of the immune system. One of us (CYoce), in collaboration with Ro- vera and with Mark M. Davis of Stan- ford University, has found that the gene for the alpha chain of the T-cell receptor lies within the region of chro- rnosome 14 that is involved in some translocations characteristic of certain cancers affecting T cells. : CHpOMOS0alE3 GENES ENCODING NEAVY-CMAIN CONSTANT REGION Our studies of tM mechanism un- derlying Burkitt's lymphoma thus have implications beyond this one dis- ease. The translocations in Burkitt's lymphoma seem to provide a model for the majority of human B-cell can- cers (and perhaps for T-cell cancers as well)L In addition knowledge of the translocation mechanism will provide powerful experimental tools not only for the study of other cancers but also for the study of the mechanisms that control genetic expression during the normal development and' function of the human immune system. GENES ENCODING MEAVYCHAM YARUIBLE REGION • C-M)C r ElCt7t+11' EXON'II EXON III CNROM06OME a GMYC EXON 11 EXON NI cxtROMOSOMe e a( the o.coae.q I. w`tcE caee oaty two e:ons moee to cbromosome 14. I. otl;er posible te.sloc.tloes the c-myc oscogroe rem.les on ekromoeome i wt.tle gens encodio= t6e cooetaot' reaion of the a.tlbody tlabt chain joi. It. 1o o.e such case (c) geaes tlat code for eo.etast rea{os oI the '9.meda^ type are tnedonted from chromosome 22; aeoes trom chromosome 2, wlicb eecode "kappa" eostaat retio.s, ea. .tco tdu part tn sucb a traasloe.tioo (d). 11 60