INDUCTION OF STRESS-RESPONSE AND DIFFERENTIAL EXPRESSION OF 70 KDA STRESS PROTEINS BY SODIUM-FLUORIDE IN HELA AND RAT-BRAIN TUMOR 9L CELLS

We herein demonstrate that sodium fluoride (NaF) acts as a stress resp onse inducer on HeLa and 9L rat brain tumor cells. NaF is only slightl y cytotoxic, and inhibitory to Ser/Thr-phosphatases but not to Tyr-pho sphatases in both cell lines. After treatment with 5 mM NaF for 2 h, t he phosphorylation levels of vimentin and an alkali-resistant 65-kDa p hosphoprotein were enhanced, a common phenomenon detected in cells und er a variety of stress conditions. Under an identical treatment protoc ol, in which the cells were treated with 5 mM NaF for 2 h and then all owed to recover under normal growing conditions for up to 12 h, NaF di fferentially induced the cytoplasmic/nuclear heat-shock protein70s (in cluding both the inducible and the constitutively expressed members of this protein family) in HeLa cells and the endoplasmic reticulum resi ding heat-shock protein70 (the glucose-regulated protein with an appar ent molecular weight of 78 kDa) in 9L cells. Electrophoretic mobility shift assays (EMSA) using probes containing well-characterized regulat ory elements revealed the activation of the heat-shock factor in HeLa but not in 9L cells; this is in good agreement with the stress protein induction pattern. Additional differential induction of binding activ ities toward EMSA probes individually containing NF-kappa B, AP-2, and CRE-like elements were detected in NaF-treated cells. The possible in volvement of these binding sites as well as the corresponding factors in the stress response are discussed. (C) 1998 Wiley-Liss, Inc.