Protein phosphorylation and metalloproteinase synthesis by lapine articular chondrocytes

Interleukin 1 (IL-1) increases the synthesis of neutral metalloproteinases (NMP) and prostaglandin E₂ (PGE₂) by primary monolayer cultures of lapine articular chondrocytes. Two-dimensional gel electrophoresis of ³²P-labelled cells confirmed that IL-1 strongly altered the pattern of phosphorylated proteins in chondrocytes. This presumably reflects modulation of the activities of protein phosphatases, kinases or both. Despite considerable experimental effort, it proved impossible to implicate activation of protein kinase C (PKC) in the responses of these cells to IL-1. Additional evidence appears also to eliminate protein kinases activated by cyclic AMP and Ca²⁺/calmodulin. Moreover, recent data further suggest that the 80 kDa IL-1 receptor is not a protein kinase. These findings increase the likelihood that a novel kinase is involved in IL-1 signalling in chondrocytes, as proposed previously for fibroblasts.