Epidermal growth factor stimulated protein kinase shows similar activity in liver of senescent and adult mice.

It was recently reported [(1983) Nature 306, 617-620] that tyrosine protein kinase activity associated with EGF receptor was absent from senescent human cultured fibroblasts, which are known to have the same number of receptors as young human cultured fibroblasts. We have measured in both adult and senescent C57 black mice the number of EGF receptors, the activity of their associated tyrosine kinase and the activity of the protein phosphatase which dephosphorylates the EGF receptor. We found our results in both groups of animals to be similar which indicate that the observations made in cultured fibroblasts cannot be generalized to all mammalian tissues.