Phorbol esters, but not the hormonal form of vitamin D, induce changes in protein kinase C during differentiation of human histiocytic lymphoma cell line (U-937)

Abstract Human histiocytic lymphoma cells (U-937) undergo similar differentiation when incubated with the phorbol ester 12-0-tetradecanoyl phorbol-13-acetate (TPA) and 1,25-dihydroxycholecalciferol. In this action, TPA somehow implicates calcium-sensitive and phospholipid-dependent protein kinase (protein kinase C), which is rapidly and significantly affected by this inducer. On the contrary, 1, 25-dihydroxy-cholecalciferol in its differentiating action does not involve protein kinase C thus suggesting that the secosteroid induces monocytic differentiation possibly through a different mechanism of that of phorbol ester.