Expression of protein kinase C (PKC) alpha, delta, epsilon, zeta in primary chick chondrocyte cultures: immunocytochemical study.

PKC is a family of 12 serine/threonine isoenzymes that plays a pivotal role in signal transduction in a large number of biological processes. In the present work we have investigated the expression of PKC (alpha, delta, epsilon, zeta) in chick chondrocyte primary cultures at different differentiation times, i.e. at 48, 55, 62 and 69 days after cell collection from tibiae of 6-day old chick embryos. We would also detect cell differentiation stages towards the osteoblast-like cell phenotype by observing the immunocytochemical expression of the specific osteoblast marker, type I collagen. At the considered culture times, cells exhibited immunocytochemical positivity for type I collagen, thus showing their differentiation towards the osteoblast-like phenotype. PKC-zeta was the isoenzyme that exhibited the most relevant immunocytochemical expression in all considered culture times, whereas PKC-epsilon always less expressed in comparison to the other PKC-isoforms. No relevant differences were observed for the immunocytochemical expressions of PKC-alpha and PKC-delta. On the basis of the immunocytochemical data obtained from the present investigation, we could affirm that PKC-alpha, -delta, -epsilon, and -zeta may play peculiar roles in the differentiation process of chick chondrocytes towards the osteoblast-like cell phenotype.

Immunochemical and immunocytochemical expression of protein kinase c isoenzymes alpha, delta, epsilon and zeta in primary adherent cultures of chick chondrocytes.

The family of protein kinase C (PKC) comprises serine/threonine isoenzymes involved in various biological processes, including cell proliferation and differentiation. On the bases of previous investigations performed by us on the expression of various PKC isoforms in the endochondral ossification process of the vertebral column, the aim of the present work was to investigate the expression of various PKC-isoenzymes in chick primary chondrocyte cultures i.e. the most used chondrocyte culture model in vitro. Immunochemical and immunocytochemical experiments were performed to detect the expression of PKC-alpha, -delta, -epsilon and -zeta. Chondrocyte cultures were examined two weeks after cell collection from tibiae of 6-day old chick embryos. By means of morphological observations associated with the immunocytochemical expression of type II collagen, two different cell phenotypes were identified, i.e. fibroblast-like and polygonal-roundish-shaped cells. As far as PKC-isoenzyme expression was concerned, PKC-zeta revealed a stronger immunochemical and immunocytochemical expression; PKC-alpha exhibited a positivity less marked than PKC-zeta, whereas PKC-delta and -epsilon were less expressed in this culture stage. It is reasonable that a major role could be played by PKC-alpha and -zeta in this phase of the chondrogenic process, whereas PKC-delta and -epsilon could be involved in different stages of chondrocyte differentiation in vitro.