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

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 8BrcAMP, and 1 μM 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 [Cys²63] 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.