Mammalian cell lines engineered to identify inhibitors of specific signal transduction pathways.

A variety of signal transduction pathways contribute to the regulation of transcription in mammalian cells. Several of these pathways ultimately rely upon the interaction of transcription factors with genetic sequences termed response elements in the promoter regions of some genes. The biochemical mechanisms that control the levels and state of activation of transcription factors are poorly understood. However, specific phosphorylation events mediated by protein kinase C, growth factor receptor-linked tyrosine kinases, and protein kinase A clearly participate in the regulation of these signal transduction pathways. To understand the relationship between activation and/or inhibition of these pathways and regulation of gene expression controlled by specific response elements, cell lines were prepared containing the TPA response element (TRE), serum response element (SRE), or cyclic AMP response element (CRE) fused to a gene encoding a secretable form of alkaline phosphatase (SEAP). These TRE-SEAP, SRE-SEAP, and CRE-SEAP cells exhibit dramatic increases in alkaline phosphatase (AP) activity following exposure to TPA, PDGF, or forskolin. Down regulation of protein kinase C or inhibition of tyrosine kinase activity blocked the stimulation of AP activity caused by TPA or PDGF. These cell lines can be used to characterize existing inhibitors, and to identify new agents that affect specific signal transduction pathways in mammalian cells.