A key role for the c-myc oncogene in cellular proliferation has long been postulated. C-myc may act by modulating the expression of other cellular genes whose products directly control proliferation. Permanent cell lines (in which the endogenous c-myc gene is tightly regulated by growth factors and cell/cell contact) have been constructed in which expression of an exogenously transfected c-myc gene is controlled by the Drosophila heat shock 70 promoter. Transcription and subsequent translation of the exogenous c-myc gene is specifically induced by mild heat shock. The endogenous c-&c gene is not expressed under these conditions. Compared to heat-shocked cell lines which contain constructs lacking c-myc, several changes in cellular gene expression are observed: (1) two-dimensional analysis of the proteins from c-myc-containing cell lines shows the induction of eight protein species and the repression of five protein species relative to cell lines lacking c-myc; (2) the transcripts of two genes (3CH77 and 3CH92), previously identified as serum inducible, are induced when c-myc is expressed; (3) attenuation of c-myc translation with c-myc antisense oligonucleotide reverses accumulation of 3CH77 and 3CH92 mRNAs; and (4) the endogenous heat shock 70 gene may be specifically induced in response to c-myc. Therefore, c-myc expression alters the expression of other cellular genes, including the induction of some known to be expressed only in proliferating cells. In order to isolate other genes specifically induced or repressed in conjunction with c-myc expression, cDNA libraries have been constructed from which hybridization subtraction may be performed and subtractive libraries made. Subtractive libraries should be enriched for specifically-induced or specifically-repressed sequences.
