Sustained and transient downregulation of Src kinases in response to nerve growth factor and epidermal growth factor, respectively.

Within a search for novel points of divergence in the signalling of differentiative nerve growth factor (NGF) and mitogenic epidermal growth factor (EGF) in PC12 cells, in the present study, I comparatively analysed the impact of these growth factors on the in situ activation status of Src kinases. By probing total cell extracts and anti-P-Tyr immunoprecipitates with a phosphorylation site-specific antibody targeting a conserved site of positive regulation of the overall family of Src kinases, a sustained and a transient downregulation of the immunoprecipitable subpopulation of nominally active Src kinases is detected in response to NGF and EGF, respectively. As the recovery of immunoreactive Src kinases is greater from cells being lysed while in suspension than from adherent cells, the possibility that NGF reduces the stability of Src kinases by upregulating cell adhesiveness is preliminarily explored and discussed.