STRUCTURE AND FUNCTION OF ONCOGENES AND ANTI-ONCOGENES

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Our research goal is to understand the molecular structure and function of the genes that play critical roles in normal growth and differentiation, neoplastic transformation, and apoptosis in mouse and human tissues and tumors of the hematopoietic system. We study oncogenes, c-myc, v-raf and v-abl; anti-oncogenes, esp. the bcl-2 family; cell cycle-regulating proteins (cyclins) and their inhibitors, p21 (waf) and p16; as well as molecules that transduce signals within the cell, e.g., protein kinase C (PKC). We and others have shown that the deregulated expression of c-myc secondary to chromosomal translocations in the c-myc region is an essential element in the series of genetic alterations that are involved in plasmacytomagenesis in BALB/c mice and in Burkitt and AIDS-associated lymphomas in man. We have also shown that c-myc can also be dysregulated in these tumor cells by retroviral insertion of strong enhancers in myc's upstream flank. It is not known why BALB/c mice are particularly susceptible to these genetic insults, but we have a candidate mechanism. We have found that the BALB/c mouse has an unusual defect in a special form of excision repair of DNA damage. This form of excision repair is unusual in that it is not coupled to RNA transcription, which is usual for DNA excision repair. Furthermore, the defect is only manifest in repair of DNA damage in the c-myc, Pvt1, switch Ig alpha and Ig kappa genes, namely the sites of recurrent chromosomal translocation in B-lymphocytic neoplasms. This is a plausible mechanism for the production of the gene-specific, strain-specific genomic instability that predisposes to the chromosome translocations that lead to constitutive expression of c-myc. This overexpression of c-myc, in turn, leads to an extension of gene-specific genetic instability to a new subset of genes, including cyclin D2. This gene becomes amplified and overexpressed in the face of c-myc overexpression, contributing to cell proliferation. We have produced a recombinant retrovirus that expresses v-abl and c-myc (ABL-MYC). This virus rapidly induces plasmacytomas in vitro and in vivo in BALB/c, nude and other strains of mice. This technology has been used to produce monoclonal antibodies to parasites, particulate, protein and peptide antigens, and it offers an alternative to hybridoma technology. We have shown that this combination of oncogenes is unique in that it permits differentiation of B cells into plasma cells in the absence of T-cell help and without ip pristane. Because T cells are not necessary in the induction of plasmacytomas with this retrovirus, we were able to show that normal T cells actually retard the emergence of these tumors. We have cloned eight PKC isozymes into expression vectors and produced cell lines that overexpress each of these isoforms in a variety of hematopoietic cell lines. Plasmacytomas are usually IL-6-dependent in vivo and in vitro, and withdrawal of IL-6 leads to their death by apoptosis. This process of apoptosis can be delayed by activating PKC-d with a specific phorbol ester. PKC-delta is also able to mediate macrophage differentiation in promyelocytes and cytoskeleton- mediated changes in the shape of B lymphocytes. We wished to determine which portion of the PKC-delta protein determines its isozyme-specific functions by constructing expression vectors that overexpress chimeric molecules that are half PKC-delta and half PKC-epsilon. The overexpression of these chimeras in different cell types showed that the C-terminal half, containing the catalytic domain, appears to bear most of the isoform-specific determinants of myeloid differentiation and transformation.