Transient Inhibition of Protein Synthesis Induces the Immediate Early Gene VL3O: Alternative Mechanism

Abstrad Indudion of gene expression in response to calcium ionophores or thapsigargin, which inhibits the calciumATPase responsible for sequestering intracellular calcium, has frequently been attributed to dired stimulatory events subsequent to the elevation of intracellular free calcium. VL3O is a murine gene that is transcriptionally induced in response to a large array of mitogenic and transforming stimuli. We have shown previously that an enhancer element within the VL3O promoter region is dependent upon cotreatment with thapsigargin or calcium ionophore for a full-scale indudion of gene expression. In this report, we demonstrate that both thapsigargin and calcium ionophores induce a transient inhibition of protein synthesis in Rat-i cells transfeded with a VL3O enhancer-driven reporter construd. Recovery of protein synthesis is facilitated by cotreatment with epidermal growth fador or phorbol esters. Furthermore, treatment with cycloheximide or Dli, which inhibit protein synthesis without altering intracellular calcium levels, can substitute for thapsigargin or ionophores in stimulating VL3O gene expression. These results suggest that the stimulatory effects of thapsigargin and calcium ionophores on VL3O expression may be mediated, at least in part, by the ability of these agents to initiate stress responses associated with the inhibition of protein synthesis.