TRANSIENT INHIBITION OF PROTEIN-SYNTHESIS INDUCES THE IMMEDIATE-EARLYGENE VL30 - ALTERNATIVE MECHANISM FOR THAPSIGARGIN-INDUCED GENE-EXPRESSION

Induction of gene expression in response to calcium ionophores or thap sigargin, which inhibits the calcium-ATPase responsible for sequesteri ng intracellular calcium, has frequently been attributed to direct sti mulatory events subsequent to the elevation of intracellular free calc ium. VL30 is a murine gene that is transcriptionally induced in respon se to a large array of mitogenic and transforming stimuli. We have sho wn previously that an enhancer element within the VL30 promoter region is dependent upon cotreatment with thapsigargin or calcium ionophore for a full-scale induction of gene expression. In this report, we demo nstrate that both thapsigargin and calcium ionophores induce a transie nt inhibition of protein synthesis in Rat-1 cells transfected with a V L30 enhancer-driven reporter construct. Recovery of protein synthesis is facilitated by cotreatment with epidermal growth factor or phorbol esters. Furthermore, treatment with cycloheximide or DTT, which inhibi t protein synthesis without altering intracellular calcium levels, can substitute for thapsigargin or ionophores in stimulating VL30 gene ex pression. These results suggest that the stimulatory effects of thapsi gargin and calcium ionophores on VL30 expression may be mediated, at l east in part, by the ability of these agents to initiate stress respon ses associated with the inhibition of protein synthesis.