Phorbol-12-myristate 13-acetate inhibits Nephronectin gene expression via Protein kinase C alpha and c-Jun/c-Fos transcription factors

Nephronectin (Npnt) is an extracellular matrix protein and ligand of integrin alpha(8)beta(1) known to promote differentiation of osteoblasts. A search for factors that regulate Npnt gene expression in osteoblasts revealed that phorbol 12-myristate 13-acetate (PMA), which activates protein kinase C (PKC), had a strong effect to suppress that expression. Research was then conducted to elucidate the signaling pathway responsible for regulation of Npnt gene expression by PMA in osteoblasts. Treatment of MC3T3-E1 cells with PMA suppressed cell differentiation and Npnt gene expression. Effects were noted at a low concentration of PMA, and were time- and dose-dependent. Furthermore, treatment with the PKC signal inhibitor Go6983 inhibited down-regulation of Npnt expression, while transfection with small interfering RNA (siRNA) of PKC alpha, c-Jun, and c-Fos suppressed that down-regulation. The present results suggest regulation of Npnt gene expression via the PKC alpha and c-Jun/c-Fos pathway.

Automated summary

The study revealed that PMA regulates Npnt gene expression in osteoblasts through the PKC alpha and c-Jun/c-Fos pathway, leading to suppression of cell differentiation. This regulation is time- and dose-dependent, and can be reversed by using PKC signal inhibitor or siRNA transfection.