1,25-DIHYDROXYVITAMIN D-3 STIMULATES THE ASSEMBLY OF ADHERENS JUNCTIONS IN KERATINOCYTES - INVOLVEMENT OF PROTEIN-KINASE-C

Signaling via intercellular junctions plays an important role in the r egulation of growth and differentiation of epithelial cells. Loss of c ell-cell contacts has been implicated in carcinogenesis, tumor progres sion, and metastasis. Here, we investigated whether 1,25-dihydroxyvita min D-3 [1,25-(OH)(2)D-3] was able to stimulate the assembly of adhere ns junctions and/or desmosomes in cultured human keratinocytes. After 4-day incubation, 1,25-(OH)(2)D-3 caused assembly of adherens junction s, but not desmosomes. The adherens junctions were identified upon kno wn ultrastructural criteria and evidence of the translocation of speci fic junctional proteins (E-cadherin, P-cadherin, alpha-catenin, and vi nculin) to the cell-cell borders. The presence of alpha-catenin and vi nculin at cell-cell borders indicated that the adherens junctions were functional. This was further supported by showing that anti E-cadheri n antibody inhibited the 1,25-(OH)(2)D-3-induce keratinocyte stratific ation. A relation between protein kinase C and adherens junction regul ation was noticed. 1,25-(OH)(2)D-3-dependent formation of junctions wa s blocked by the inhibitors of protein kinase C, bisindolylmaleimide a nd 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine (H-7), and treatmen t of keratinocytes with 1,25-(OH)(2)D-3 caused a rapid activation of p rotein kinase C and its translocation to the membranes. Formation of i ntercellular contacts may be an important mechanism of 1,25-(OH)(2)D-3 action in hyperproliferative and neoplastic diseases.