The long-term objectives are to define molecular mechanisms by which specific translocations lead to apparent transcriptional activation of the cellular proto-oncogenes in Burkitt's lymphoma (BL), an undifferentiated B-lymphocyte cancer of man, and other hematopoietic cancers. The mechanism of c-myc activation will be examined initially by: (1) molecular cloning and characterization of the Ramos BL c-myc alleles; (2) characterization of the c-myc transcript; and (3) transfection of molecular clones of c-myc into B-lymphoid cells to study the expression of the transferred c-myc genes. A recombinant DNA library will be constructed and phage clones containing c-myc gene will be identified by in situ hybridization screening of plaques. Cloned c-myc genes will be characterized to identify key structural differences between the normal and rearranged alleles that might be related to their functional differences. The structure of the c-myc transcripts will be examined by Northern blotting and S?1? nuclease mapping techniques. These studies will test the hypothesis that the effects of c-myc in Ramos BL is due to overexpression of a normal c-myc transcript (gene dosage model of malignancy). Finally, to detect the possible presence of a transcriptional enhancer sequence adjacent to the rearranged Ramos c-myc allele, the isolated c-myc alleles will be cloned into the shuttle vector pSV2-neo. These constructs will be transfected into NIH 3T3 cells and B-lymphoblastoid cell lines to detect differences in expression and regulation between the normal and rearranged c-myc allele responsible for enhanced expression. Transfection studies might also reveal differences in the ability of fibroblasts versus lymphoid cells to detect certain classes of activated proto-oncogenes. Although BL responds to chemotherapy, early clinical relapse after remission is often characterized by resistance to further therapy and a poor prognosis. Illumination of mechanisms of enhanced expression of c-myc in BL and its biological role in the genesis of this lymphoma might suggest whether this pathway is a potential target for experimental intervention. Results from these studies may be relevant to other proto-oncogenes structurally and functionally related to c-myc, and thus to other cancers in which aberrant expression of these genes might have a role in the genesis or maintenance of the malignant phenotype. (X)
