STRUCTURE AND FUNCTION OF ONCOGENES AND ANTI-ONCOGENES

点击翻译按钮获取中文摘要

Our research goal is to understand the molecular structure and function of the genes that play critical roles in malignancy, cell growth and normal differentiation. We are concentrating on a group of known oncogenes and anti-oncogenes: c-myc, abl, cbl, the bcl-2 family, the ras family and p53, p21 (waf), p107, as well as potential oncogenes: Pvt-1 and the isoforms of protein kinase C (PKC) in mouse and human tissues and tumors. 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. A "variant" subgroup of these myc-activating translocations occurs approximately 260kb 3' of c-myc in a region designated Pvt-1. We have shown that most of these variant translocations lead to the synthesis of a chimeric mRNA that includes a portion of Pvt-1 and the constant region of the kappa Ig light chain. This chimeric product may play a role in plasmacytoma development or in increasing c-myc expression. We have shown that the BALB/c mouse has an unusual defect in a special form of excision repair. The defect is only manifest in repair of DNA damage in the Pvt-1, c-myc, switch IgA and Ig kappa constant region genes, namely the sites of recurrent chromosomal translocation in mouse and human B-lymphocytic neoplasms. This form of excision repair is also unusual in that it is not coupled to RNA transcription, which is the case for most forms of DNA excision repair. We have produced a recombinant retrovirus that expresses v-abl and c- myc (ABL-MYC). This virus rapidly induces plasmacytomas in 100% of BALB/c mice. If the mice are immunized before infection with ABL-MYC, approximately 50% of the plasmacytomas produce antibodies that are directed toward the immunogen. This technology has been used to produce monoclonal antibodies to particulate, protein and peptide antigens, and it offers an alternative to hybridoma technology. This approach also works if immunized mouse B lymphocytes are infected in vitro and transplanted into syngeneic hosts. 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, in the absence of pristane priming and in the absence of helper virus. Because T cells are not necessary in the induction of plasmacytomas with this retrovirus, we are able to show that T lymphocytes actually retard the emergence of these tumors. We have cloned eight isozymes of the PKC family into expression vectors and produced cell lines that overexpress each of these isoforms in NIH3T3 fibroblasts. Immunohistochemistry has shown that each isoform translocates to different intracellular organelles when activated by phorbol esters, indicating that the substrate for each isoform is restricted to these sites. We have studied the roles of the PKC isoforms in lymphocyte growth and development. Plasmacytomas are usually IL-6-dependent in vivo and in vitro, and we have determined that withdrawal of IL-6 leads to their death by apoptosis. This process of apoptosis can be delayed by treatment with phorbol esters, implicating one or more isoforms of PKC in the prevention of apoptosis.