ORGANIZATION AND CONTROL OF GENETIC MATERIAL IN PLASMACYTOMAS

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Our research goal is to understand the genes whose altered structure or expression play critical roles in malignancy, cell growth and normal differentiation. We are concentrating on the study of the expression of a group of known oncogenes: abl, bcl-2 and myc, as well as potential oncogenes: Pvt-1, protein kinases C (PKC) and cyclins, in mouse hematopoietic tissues and tumors. Deregulated expression of myc secondary to chromosomal translocations has been shown to be one essential element in the series of genetic alterations that are involved in oil-induced plasmacytomas in BALB/c mice. Some of these myc-activating translocations occur 200-300 kb 3' of c-myc in a region designated Pvt-l. We have shown that Pvt- l and c-myc are co-amplified in a series of B-cell lymphomas and expressed at a very high level. Pvt-l expression utilizes alternative splicing of numerous exons, including one that may be as far as l Mb 3' of c-myc. We have recently identified three areas of structural similarity between the Pvt-l genes of mouse and man. This evolutionary conservation suggests strongly that Pvt-1 is a gene of considerable importance to normal cellular metabolism. The ABL-MYC retrovirus, that expresses v-abl and c-myc, rapidly induces i.p. plasmacytomas in BALB/c mice. This transformation also works in vitro if the virus is used to infect suspensions of lymphoid cells that are subsequently transplanted into syngeneic mice. This works even if the cells are early B lymphocyte precursors, i.e., pro-B or pre-B cells. If the mice are immunized before induction of plasmacytomas, 50% of them develop tumors that produce antibodies that are directed toward the immunogen. This technology has been used to produce monoclonal antibodies to several protein and peptide antigens. These results suggest that the most efficient B-cell transformation by ABL-MYC occurs in mature, committed B lymphocytes. Eight isozymes of the PKC family have been shown by us to be expressed in a cell-type specific fashion in hematopoietic cells and cell lines. Expression vectors that stably overexpress all of these isoforms have been prepared. Overexpression of certain of these PKCs in NIH3T3 cells has proved to be transforming in vitro and tumorigenic in nude mice. Similarly, overexpression of these PKC isoforms in a mouse myeloid cell line, 32D, has been shown to impart to these cells the ability to differentiate into macrophages when exposed to phorbol esters. Cyclins B1, D1, D2 and D3 have been cloned and used to identify the chromosome that bears these genes. Expression of these cyclins in hematopoietic tumors has been shown to be cell-type specific.