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. We study oncogenes, particularly c-myc, v-raf, v-abl and v- and c-cbl; anti-oncogenes, esp. the cell cycle-regulating proteins (cyclins) and their inhibitors, p21 (waf) and p16; the bcl-2 family; as well as molecules that transduce signals within the cell, esp., 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. It is not known why BALB/c mice are particularly susceptible to these genetic aberratons, 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, unlike most forms of DNA excision repair it is not coupled to RNA transcription. Furthermore, the defect is only manifest in repair of DNA damage in the c-myc, Pvt1, switch Ig a and Ig k genes, namely the sites of recurrent chromosomal translocations in B-lymphocytic neoplasms. This is a plausible mechanism for the production of the gene- specific, strain-specific genomic instability that predisposes BALB/c mice to the chromosome translocations that lead to constitutive expression of c-myc. This dysregulated expression of c-myc, in turn, leads to an extension of gene-specific genetic instability to a new subset of genes, including cyclin D2, RNR2 (subunit 2 of ribonucleotide reductase) and dihydro- folate reductase (dhfr). This subset of genes uniquely becomes amplified and overexpressed as a response to c-myc overexpression, possibly contributing to uncontrolled cell proliferation. We have cloned eight Protein Kinase C (PKC) isozymes into a variety of expression vectors and produced cell lines that overexpress each of these isoforms. We have also produced chimeric PKC molecules, i.e., half PKC-d and half PKC-e, and cell lines that overexpress them, to determine whether the regulatory half or the catalytic half controls various functions of PKC. PKC-d is able to mediate TPA-induced macrophage differentiation of promyelocytes, while overexpression of PKC-e in rodent fibroblasts is transforming in vitro and tumorigenic in vivo. Overexpression of the PKC chimeras showed that the C-terminal half, containing the catalytic domain, appears to bear most of the isoform- specific determinants of myeloid differentiation and fibroblast transformation.