Proliferation, inositol trisphosphate

In osteoblasts, keratinocytes, and colonocytes, andpossibly other cells, calcitriol acts via cell surface receptors linked to phospholipase C, resulting in release of diacylglycerol and inositol trisphosphate (Section 14.4.1), followed by opening of intracellular calcium channels and activation of protein kinase C and mitogen-activated protein (MAP) kinases. The effect of this is inhibition of cell proliferation and induction of differentiation. A variety of analogs of calcitriol that do not bind to the nuclear receptor do bind to, and activate, the cell surface receptor, including l,25-dihydroxy-7-dehydrocholesterol and 1,25-dihydroxylumisterol. The rapid nongenomic responses to vitamin D can be demonstrated in knockout mice that lack the vitamin D nuclear receptor (Farach-Carson and Ridall, 1998 Nemere and Farach-Carson, 1998). 

Figure 32.3 Inhibitory effects of iodide on human thyrocytes function, r, iodide NiS, sodium iodide symporter DUOX, duai oxidase TPO, thyroperoxidase TG, thyroglobulin TGI, iodinated thyroglobuiin X, the substrate converted into the active inhibitory iodinated molecule XI micro, micropinocytosis macro, macropinocytosis prolif, proliferation G.I., gene induction R, receptor Gs, stimulatory G protein of adenylyl cyclase AC, adenylyl cyclase cAMP, cyclic 3 -5 adenosine monophosphate PGE, prostaglandin E1 NE, norepinephrine Gq, stimulatory G protein of phospholipase C DAG, diacylglycerol IPS, inositol 1,4,5-trisphosphate Aa, amino acid ...

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