NITRIC-OXIDE INHIBITS THE SYNTHESIS OF TYPE-II COLLAGEN WITHOUT ALTERING COL2A1 MESSENGER-RNA ABUNDANCE - PROLYL HYDROXYLASE AS A POSSIBLE TARGET

The addition of human recombinant interleukin-1 beta (IL-1 beta) to cu ltures of lapine articular chondrocytes provoked the synthesis of larg e amounts of NO and reduced the production of type-II collagen. N-G-Mo nomethyl-L-arginine (L-NMA), an inhibitor of NO synthase, strongly sup pressed the production of NO and partially relieved the inhibition of collagen synthesis in response to IL-1 beta. The NO donor S-nitrosoace tylpenicillamine (SNAP), on the other hand, inhibited collagen product ion. IL-1 lowered the abundance of Col2A1 mRNA in an NO-independent ma nner. Collectively, these data indicate that IL-1 suppresses collagen synthesis at two levels: a pretranslational level which is NO-independ ent, and a translational or post-translational level which is NO-media ted. These effects are presumably specific as L-NMA and SNAP had no ef fect on total protein synthesis or on the distribution of newly synthe sized proteins between the cellular and extracellular compartments. Pr olyl hydroxylase is an important enzyme in the post-translational proc essing of collagen, and its regulation and cofactor requirements sugge st possible sensitivity to NO. Extracts of cells treated with IL-1 or SNAP had lower prolyl hydroxylase activity, and L-NMA was partially ab le to reverse the effects of IL-1. These data suggest that prolyl hydr oxylase might indeed be a target for NO. Because under-hydroxylated co llagen monomers fail to anneal into stable triple helices, they are de graded intracellularly. Inhibition of prolyl hydroxylase by NO might t hus account for the suppressive effect of this radical on collagen syn thesis.