ACTIVATION OF PHOSPHOLIPASE-C BY HEAT-SHOCK REQUIRES GTP ANALOGS AND IS RESISTANT TO PERTUSSIS TOXIN

The heat shock response in mammals consists of a complex array of intr acellular reactions initiated by stress, although its regulation is po orly understood. We have investigated the role of transmembrane signal transduction in the response, examining mechanisms involved in the ac tivation of phospholipase C (PLC) by heat shock. In rodent fibroblasts permeabilized with digitonin, heat shock and receptor-mediated PLC ac tivity exhibited a strict GTP analog dependency. This indicates that h eat shock-mediated phopholipase activation, in common with receptor me diated stimulation, does not involve direct effects on the phospholipa ses and suggests the participation of GTP binding (G) proteins in the activation process. When cells were treated with the inhibitor pertuss is toxin (PTX), the phospholipases retained their inducibility by heat shock, but became refractory to thrombin treatment, indicating that h eat shock may influence PLC activity through a distinct population of G proteins compared to thrombin. The data seem to exclude a role for P TX sensitive G proteins in the production of IP3 after heating and sug gest a pathway involving the direct thermal activation of the G(q) cla ss of G proteins, which are coupled to the PLC(beta1) isoform. (C) 199 3 Wiley-Liss, Inc.