TYROSINE KINASES ARE INVOLVED WITH THE EXPRESSION OF INDUCIBLE NITRIC-OXIDE SYNTHASE IN HUMAN ARTICULAR CHONDROCYTES

The present study characterizes mechanisms involved with the induction of nitric oxide (NO) production, nitric oxide synthase (NOS) enzymati c activity and mRNA expression in human articular chondrocytes. Activa tion of chondrocytes with lipopolysaccharide (FPS) or IL-l resulted in time- and dose-dependent increases in iNOS mRNA followed by increased NOS enzymatic activity and NO release. The protein tyrosine kinase (P TK) inhibitors herbimycin A or genistein reduced IL-l or LPS-induced N O release and NOS enzymatic activity. This was associated with inhibit ion of iNOS mRNA expression as determined by reverse transcription-pol ymerase chain reaction (RT-PCR) and in situ hybridization. In contrast , inhibitors of protein kinase C (PKC) or protein kinase A (PKA) did n ot affect these responses. These results were confirmed in experiments with second messenger agonists where neither activation of PKC, nor i ncreases in cyclic adenosine monophosphate (cAMP) or increased intrace llular calcium levels were associated with the induction of iNOS mRNA or NO release. These results suggest that PKC, PKA and calcium-depende nt signals are not required or sufficient for the stimulation of NO pr oduction. However, NO production is dependent on tyrosine kinases due to their role in the expression of iNOS mRNA. (C) 1995 Wiley-Liss, Inc .