Parathyroid hormone-related protein increases DNA synthesis in proximal tubule cells by cyclic AMP- and protein kinase C-dependent pathways

Abstract

The present study was performed to characterize the possible involvement of cAMP synthesis and protein kinase C (PKC) activation in the DNA synthesis-stimulating effect of parathyroid hormone-related protein (PTHrP) in proximal tubule cells. We found that DNA synthesis was stimulated by 10 μM SBrcAMP, and 1 uM Sp-cDBIMPS, two cAMP analogs, and also by 1 μM phorbol 12-myristate 13-acetate (PMA) and 100 μM 1,2-dioctanoyl-sn-glycerol, two PKC activators, and 10 nM [Cys 23] human (h)PTHrP (24–35) amide in rabbit proximal tubule cells (PTC). Both Sp-cDBIMPS and PMA, at 1 μM, also increased DNA synthesis in SV-40-immortalized mouse proximal tubule cells MCT. Human PTHrP (7–34) amide [PTHrP (7–34)] dose dependently stimulated DNA synthesis in a similar manner as [ 34Tyr]PTHrP (1–34) amide [PTHrP (1–34)], in PTC. PMA pre-treatment for 20 h, which downregulates PKC, completely blocked the effect induced by PTHrP (7–34), but not that of PTHrP (1–34), in the latter cells. In contrast, the same PMA pre-treatment abolished the DNA synthesis stimulation by PTHrP (1–34) and PTHrP (7–34) in MCT cells, which appear to have PTH receptors mainly coupled to phospholipase C and not adenylate cyclase. Our results indicate that the stimulatory effect of PTHrP on DNA synthesis in proximal tubule cells is mediated by a cAMP- and PKC-dependent mechanism.