Proliferating cell nuclear antigen (PCNA) and fibroblast growth factor receptor one (FGFR1) expression as indicators of rat satellite cell activation.

Abstract

Rat satellite cells from young animals become activated and commence division sooner in culture than satellite cells from adult animals. Differences in the length of this lag period may be attributed to differences in expression of cell surface receptors, signal transduction or DNA replication capacity. To examine this period, an ELISA was developed to monitor proliferating cell nuclear antigen (PCNA) expression. Results indicated that PCNA is expressed earlier in cultures from young rats than in cultures from adult rats with an increase in PCNA levels occurring at 30 and 48 hours, respectively. Addition of basic fibroblast growth factor (bFGF), a mitogen for satellite cells, at the time of plating enhanced PCNA expression in young but not adult rat satellite cells. These results suggest that the adult cells may not express FGF receptors (FGFR) or that the receptor fails to generate a signal. Analysis of FGFR expression indicated that FGF receptors were present in satellite cells from young rats at 18 hours post-plating and in cells from adult rats at 42 hours post-plating. Western analysis demonstrated that the receptor present was the full length FGF receptor one (FGFR1). FGFR1 mediated the tyrosine phosphorylation of proteins with molecular weights of 150, 145, 90, 42 and 35 kDa upon addition of bFGF. The presence of a functional FGFR1 prior to PCNA expression suggests that the expression of FGFR1 can be used as a marker for entry of satellite cells into G₁ phase of the cell cycle. The ability of the cells from the young animals to become active sooner than their adult counterparts may be due to the length of time the adult cells have been quiescent. Depth of quiescence may be an important determinant in activation of satellite cells.