Role of Protein Kinase C α in Primary Human Osteoblast Proliferation

Abstract

Protein kinase C (PKC) isoforms have been shown to have specific expression profiles and individual isoforms are believed to play distinct roles in the cells in which they are found. The goal here was to determine which specific isoform(s) is involved in proliferation of primary human osteoblasts. In primary human osteoblasts, 10 M of acute sphingosine-1-phosphate (S1P) treatment induced an increase in proliferation that correlated with an increase in PKC␣ and PKC expression. To further delineate which isoforms are involved in osteoblastic cell proliferation, the effect of low versus high serum culture conditions on PKC isoform expression was determined. Likewise, the effect of antisense oligodeoxynucleotides (ODNs) to specific PKC isoforms on proliferation and MAPK activation was studied. The effect of S1P on intracellular translocation of activated PKC isoforms was also evaluated. The results indicated that in primary human osteoblasts, PKC␣ was not expressed under conditions of low proliferative rate while PKC␦ and PKC expression was not affected. The specific inhibition of PKC␣ by antisense ODNs resulted in inhibition of MAPK activity leading to a significant decrease in proliferation. S1P up-regulated antisense ODN inhibited PKC␣ expression and MAPK activity and led to an increase in proliferation. Subsequent experiments using platelet-derived growth factor (PDGF) as an additional mitogen generated similar data. PDGF stimulation resulted in a significant increase in proliferation that correlated with an up-regulation of inhibited PKC␣ expression in antisense ODN-treated cells. Immunofluorescence methods showed that mitogenic stimulation of PKC␣ resulted in nuclear translocation. Our findings present original data that PKC␣ is the isoform specifically involved in the proliferation of primary human osteoblasts. (J Bone Miner Res 2002;17:1968 -1976

The expression profile of PKC isoforms during MC3T3-E1 differentiation

“…The expression of PKC · continued to increase throughout the proliferative stages of MC3T3-E1 OBC. This pattern of expression is in accord with previous studies (22,31). In primary rat OBC there is a continuous increase in PKC · expression from early to late cell cultures.…”

Effects of platelet-derived growth factor, vitamin D and parathyroid hormone on osteoblasts derived from cancer patients on chronic bisphosphonate therapy

“…3 H]-thymidine using a methodology previously described for osteoblastic cells from the alveolar bone (13). Once the cell cultures from the donor bones reached 70% confluency, they were detached by trypsinization and cultured in 24-well plates at a density of 50,000 cells/well.…”

Bioluminescence imaging in bone tissue engineering

“…It has been reported that the protein kinase C (PKC) signalling pathway is involved in osteoblast proliferation and differentiation [98][99][100]. Thus, in chapter 2, we have investigated the role of the PKC family in the context of hMSCs osteogenic differentiation in vitro.…”

“…Some reports show that certain PKC isozymes are involved in osteogenic differentiation or osteoblast proliferation. For instance, PKCδ and PKCμ, are known to be involved in osteogenic differentiation in murine cells and animal models and PKCα has been implicated in human osteoblasts proliferation [98,100,144]. We treated hMSCs with PKC activators and inhibitors to investigate cell proliferation and differentiation in vitro, and observed that different PKC subfamilies had opposite roles in ALP expression and mineralization.…”

“…PGE2 stimulates human bone cells by inducing PLC (Ca/PKC) [127]. Furthermore it has been Chapter 2 demonstrated that the PKC-isoform is involved in proliferation of primary human osteoblasts [98].…”