REGULATION OF CONNEXIN43 EXPRESSION AND FUNCTION BY PROSTAGLANDIN E-2(PGE(2)) AND PARATHYROID-HORMONE (PTH) IN OSTEOBLASTIC CELLS

Connexin43 (Cx43) forms gap junctions that mediate intercellular commu nication between osteoblasts. We have examined the effects of prostagl andin E-2 (PGE(2)) and parathyroid hormone (PTH) on gap junctional com munication in the rat osteopenic sarcoma cells UMR 106-01. Incubation with either PGE(2) or PTH rapidly (within 30 min) increased transfer o f negatively charged dyes between UMR 106-01 cells. This stimulatory e ffect lasted for at least 4 h. Both PGE(2) and PTH increased steady-st ate levels of Cx43 mRNA, but only after 2-4 h of incubation. Transfect ion with a Cx43 gene construct linked to luciferase showed that this e ffect of PTH was the result of transcriptional upregulation oi Cx43 pr omoter. Stimulation of dye coupling and Cx43 gene transcription were r eproduced by forskolin and 8Br-cAMP. Exposure to PGE(2) for 30 min inc reased Cx43 abundance at appositional membranes in UMR 106-01, whereas total Cx43 protein levels increased only after 4-6 h of incubation wi th either PGE(2) or PTH. inhibition of protein synthesis by cyclohexim ide did not affect this early stimulation of dye coupling, but it sign ificantly inhibited the sustained effect of PTH and forskolin on cell coupling. In summary, both PTH and PGE(2), presumably through cAMP pro duction, enhance gap junctional communication in osteoblastic cell cul tures via two mechanisms: initial rapid redistribution of Cx43 to the cell membrane, and later stimulation of Cx43 gene expression. Modulati on of intercellular communication represents a novel mechanism by whic h osteotropic factors regulate the activity of bone forming cells. (C) 1998 Wiley-Liss, Inc.