REGULATION OF HSP70 BY PTH - A MODEL OF GENE-REGULATION NOT MEDIATED BY CHANGES IN CAMP LEVELS

Parathyroid hormone (PTH) activates both adenylate cyclase and phospho lipase C in target cells, and cloned PTH/PTH-related protein (PTHrP) r eceptor can mediate both responses when expressed in host cells such a s LLC-PK1 renal epithelial cells. Because calcitonin (CT) is known to augment 70-kDa heat shock. protein (HSP70) mRNA by an adenosine 3',5'- cyclic monophosphate (cAMP)-independent mechanism in LLC-PK1 cells, we examined regulation of HSP70 transcription by PTH in these cells. Lik e CT, human PTH-(1-34) [hPTH-(1-34); 10(-10) to 10(-7) M)] increased p orcine HSP70 mRNA and human HSP70 promoter-chloramphenicol acetyltrans ferase (CAT) expression within 4 h in LLC-PK1 cells that stably expres s greater than or equal to 100,000 PTH/PTHrP receptors per cell. The e ffect of PTH on HSP70 mRNA was not mimicked by cAMP analogues, forskol in, phorbol esters, Ca2+ ionophores, or alpha-thrombin; was insensitiv e to pertussis toxin; and was not due to increased mRNA stability. The upregulation of HSP70 gene transcription by hPTH (and CT) was clearly observed even after deletion of the functional heat shock consensus e lement in the promoter region of the human HSP70/CAT reporter. Upregul ation of HSP70 transcription via endogenous PTH receptors also was obs erved in the osteoblastic cell lines SaOS-2 and ROS 17/2.8. Regulation of HSP70 gene transcription by PTH may be a common cellular response to the hormone, which, in some cells, may not be mediated by activatio n of adenylate cyclase or protein kinase C.