STIMULATION OF OSTEOPONTIN MESSENGER-RNA EXPRESSION IN HL-60 CELLS ISINDEPENDENT OF DIFFERENTIATION

12-O-Tetradecanoylphorbol 13-acetate (TPA) induces HL-60 cells to diff erentiate along the monocyte/macrophage pathway and stimulates express ion of the extracellular adhesion protein osteopontin (OPN). In this s tudy, the mechanism of TPA-mediated OPN mRNA expression and its relati onship to differentiation were investigated. The induction of OPN mRNA by TPA was dose dependently inhibited by staurosporine (0.4-10.0 nM) and chelerythrine (01.1-5.0 mu M), indicating that OPN expression requ ires PKC activation, Furthermore, the mitogen-activated protein kinase kinase (MAPKK) inhibitor, PD 098059 (1.0-10.0 mu M), inhibited the ef fect of TPA in a dose-dependent fashion, Cycloheximide (10 mu g/ml) ab lated the induction of OPN mRNA by TPA. To determine if OPN mRNA expre ssion was associated with a particular differentiational pathway, HL-6 0 cells were treated with RA, 9-cis-RA, calcitriol, or sodium butyrate , None of these agents stimulated OPN mRNA. Treatment with TPA subsequ ent to a 120-h pretreatment with retinoic acid (RA), 9-cis-RA, or calc itriol resulted in a potentiation of the induction of OPN mRNA. These results support a role for protein kinase C (PKC) in promoting OPN exp ression because each of these agents increased PKC levels. An hOPN pro moter/reporter construct was responsive to TPA, indicating that this e ffect is at the level of transcription. Thus, TPA-stimulated transcrip tion of the OPN gene apparently occurs via a PKC/MAPK-dependent mechan ism that is independent of that associated with differentiation and is not dependent on the maturational state of these cells. (C) 1997 Acad emic Press.