1,25-Dihydroxyvitamin D3 Stimulates Expression and Translocation of Protein Kinase Cα and Cδ via a Nongenomic Mechanism and Rapidly Induces Phosphorylation of a 33-kDa Protein in Acute Promyelocytic NB4 Cells
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abstract
1,25-Dihydroxyvitamin D3 (1,25-(OH)2D3) primes NB4 cells for 12-O-tetradecanoylphorbol-13-acetate-induced monocytic differentiation in a dose- and sequence-dependent fashion. Experiments utilizing 1,25-(OH)2D3 analogues and kinase/phosphatase inhibitors suggested that tyrosine kinase and serine/threonine phosphorylation cascades, rather than vitamin D3 receptor-mediated signals, were involved in 1,25-(OH)2D3 action. Here we show that NB4 cells express the alpha and delta (but not the beta, epsilon, and theta) isoforms of protein kinase C (PKC). Both authentic 1, 25-(OH)2D3 and the nongenomic analogue 1alpha,25-dihydroxyprevitamin D3 (HF) increased expression of PKCalpha and PKCdelta. PKCalpha and PKCdelta were translocated to the nucleus of the cell in response to 1,25-(OH)2D3 or HF. The effects of HF were attenuated by the nongenomic antagonist 1beta,25-dihydroxyvitamin D3, suggesting that changes in PKC expression are mediated by a nongenomic signaling pathway. Consistent with the involvement of serine, threonine, and tyrosine phosphorylation cascades mediating 1,25-(OH)2D3 action, enhanced phosphorylation of a variety of cellular proteins at serine and threonine residues and the specific enhanced phosphotyrosyl content of a 33-kDa protein (vdrp33) were observed immediately after 1,25-(OH)2D3 addition. We propose that 1,25-(OH)2D3 primes NB4 cells for 12-O-tetradecanoylphorbol-13-acetate-induced monocytic differentiation by increasing the expression of specific PKC isoforms and inducing the specific phosphorylation of key protein signaling intermediates.
