MODULATION OF PROTEIN-PHOSPHORYLATION AND STRESS PROTEIN EXPRESSION BY OKADAIC ACID ON HEAT-SHOCK CELLS

We have demonstrated that pretreatment but not post-treatment with oka daic acid (OA) can aggravate cytotoxicity as well as alter the kinetic s of stress protein expression and protein phosphorylation in heat sho cked cells. Compared to heat shock, cells recovering from 1 hr pretrea tment of OA at 200 nM and cotreated with heat shock at 45 degrees C fo r the last 15 min of incubation (OA --> HS treatment) exhibited enhanc ed induction of heat shock proteins (HSPs) 70 and 110. In addition to enhanced expression, the attenuation of HSC70 and HSP90 after the indu ction peaks was also delayed in OA --> HS-treated cells. The above tre atment also resulted in the rapid induction of the 78 kDa glucose-regu lated protein (GRP78), which expression remained constant in cells rec overing from treatment with 200 nM OA for 1 hr, heat shocked at 45 deg rees C for 15 min, or in combined treatment in reversed order (HS --> OA treatment). Enhanced phosphorylation of vimentin and proteins with molecular weights of 65, 40, and 33 kDa and decreased phosphorylation of a protein with a molecular weight of 29 kDa were also observed in c ells recovering from OA --> HS treatment. Again, protein phosphorylati on in cells recovering from HS --> OA treatment did not differ from th ose in cells treated only with heat shock. Since the alteration in the kinetics of stress protein expression and protein phosphorylation was tightly correlated, we concluded that there is a critical link betwee n induction of the stress proteins and phosphorylation of specific pro teins. Furthermore, the rapid induction of GRP78 under the experimenta l condition offered a novel avenue for studying the regulation of its expression. (C) 1996 Wiley-Liss, Inc.