Gene Expression and Signal Transduction in Transformatio

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The chief objective of our research is to understand the molecular and genetic mechanisms responsible for differentiation, cell growth, and neoplastic transformation. We study the oncogenes, tumor-suppressor genes and signal-transducing proteins in mouse and human experimental tumor systems, including BALB/c mouse plasmacytomas, B-cell lymphomas, and NIH 3T3 cells, among others. These are valuable experimental models, because they can be used to devise more specific therapy and preventive measures for human multiple myeloma, non-Hodgkin's lymphomas, and other human malignancies. BALB/c plasmacytomas, like human Burkitt lymphomas, are characterized by constitutive expression of the proto-oncogene, c-Myc. To determine which additional genetic alterations are required for complete transformation, we are using microarray hybridization studies of global gene expression to follow changes in gene expression during progression from pre-malignant to fully malignant plasma cell tumors. We are also using microarray hybridization studies to probe the pathophysiological mechanisms at work in development of plasma cell tumors in mice and the mechanisms whereby certain transgenes and viral oncogenes accelerate this neoplastic process.In the study of signal transduction in differentiation and neoplastic transformation, we are investigating the isoform-specific features of the protein kinase C (PKC) family of serine/threonine kinases. We have been focusing on the delta and epsilon isoenzymes, which have opposing effects on cell proliferation. We have shown that most of the isoenzyme-specific determinants are located in the catalytic half (the carboxyl-terminal domain) of these PKCs by creating reciprocal chimeric cDNAs that encode molecules that are half PKC-delta and half PKC-epsilon. We are further dissecting the structure of the catalytic domain to determine which sub-domains determine PKC isoform- specific functions, focusing on the carboxy-terminal 50 amino acids, the "V5 domain." We are also studying the nature of PKC's involvement in apoptosis, in cytoskeleton-related changes in cell shape and motility, and in cooperation with the c-myc proto-oncogene. We have shown that phorbol ester-activation of overexpressed PKC-delta disrupts the actin cytoskeleton in human and mouse lymphocytes, leading to the loss of membrane ruffling, a surface alteration needed for cell movement, and the loss of the typical elongated shape of these cells. We have demonstrated that this effect is due to PKC-mediated changes in phosphorylation of key tyrosine residues in the adaptor molecule, paxillin.