GENOMIC EFFECTS OF THE PUTATIVE ONCOGENE G-ALPHA-S - CHRONIC TRANSCRIPTIONAL ACTIVATION OF THE C-FOS PROTOONCOGENE IN ENDOCRINE-CELLS

Somatic mutations of the a subunit of Gs (G alpha s) have been detecte d in a variety of endocrine tumors. To test whether G alpha s is an on cogene, we investigated the genomic effects of G alpha s protein in wh ich the GTPase activity had been inactivated. Results from transient t ransfection studies show that such proteins increase 1) transcription of a reporter gene driven by the minimal cAMP-responsive element (TGAC GTCA) and 2) c-fos transcription in several endocrine cell lines (GH3, AtT20, and PC12). By promoter deletion analyses and genetic inactivat ion of cAMP-dependent protein kinase, we show that this transcriptiona l stimulation by G alpha s impinges on several regulatory elements wit hin the c-fos promoter and operates within the protein kinase A pathwa ys. Stable PC12 cell lines were established to analyze long-term effec ts of constitutively active G alpha s. Cell lines expressing mutated G alpha s have elevated cAMP levels and increased AP1 binding activity. Transcription of a variety of genes, including c-fos, c-jun, and junB , is increased in these cells. The strong and permanent effects of G a lpha s on early immediate genes, and c-fos in particular, may be respo nsible for the oncogenic potential of G alpha s in endocrine cells.