Expression of Protein Kinase C Isozymes That Are Required for Chondrogenesis of Chick Limb Bud Mesenchymal Cells

Abstract

Protein kinase C (PKC) has been suggested to be involved in the chondrogenesis of chick limb bud mesenchymal cells. This study examined the expression and the role of PKC isozymes in chondrogenesis. Multiple PKC isozymes such as conventional PKC (cPKCα and γ), new PKC (nPKCϵ), and atypical PKC (aPKCζ, λ, and ι) were expressed in chondroblasts but cPKCβ and nPKCδ were not detected. The amounts of expressed cPKC and nPKC isozymes, namely cPKCα and γ and nPKCϵ, were increased as chondrogenesis proceeds while the level of aPKC isozymes was not changed. Treatment of cells with specific PKC inhibitors blocked chondrogenesis. Prolonged exposure of cells to phorbol ester which down regulates both cPKC and nPKC also blocked chondrogenic differentiation. The inhibition of chondrogenesis was the most effective when PKC activity was blocked at the early stage of chondrogenesis (i.e., for the first 24 hours of micromass culture). Down regulation of PKC blocked both proliferation of cells and synthesis of sulfated proteoglycans, indicating that expression of cPKC and nPKC is required at early stage of chondrogenesis.