Cellular responsiveness to epidermal growth factor (EGF) and the structure of the receptor for epidermal growth factor (EGF-R) were compared in young and senescent human fibroblast (HF) cells. Biosynthetic labeling of HF cells with [35S]methionine followed by immunoprecipitation with EGF-R antibody revealed the presence of Mr 170 000 EGF-R in cells from both stages. Autophosphorylation of EGF-R in response to EGF was identical in young and senescent cells. Phosphoamino acid analysis of the autophosphorylated EGF-R indicated that tyrosine residues were phosphorylated in each preparation. Two-dimensional peptide mapping of [125I]EGF-R from young and senescent cells showed essentially the same pattern, indicating the EGF-R does not apparently undergo detectable changes in senescent human fibroblasts. The responsiveness of aging HF cells to EGF for the induction of ornithine decarboxylase activity and for the production of secretory proteins was measured. Young and senescent HF cells showed about a three-fold induction of collagenase activity upon addition of EGF. Ornithine decarboxylase activity was also stimulated by EGF to a comparable level in young and senescent cells. Our results indicate that the responsiveness of HF cells to EGF for these two biochemical parameters does not decline with the loss of proliferative activity.
All Science Journal Classification (ASJC) codes
- Developmental Biology