If the third mechanism occurred in MCFA cells, then 1 would predict that phosphorylation of Akt on serine should also be very similar at each cell densities. This was not observed in our experiments . Consequently, only the primary two mechanisms of Akt activation are compatible with our data. Together with regulation by serine and threonine phosphorylation, Akt is regulated by tyrosine phosphorylation . EGF therapy induces tyrosine phosphorylation of Akt in COS cells . This EGF dependent tyrosine phosphorylation of Akt can be inhibited by PP, a selective inhibitor of Src family tyrosine kinases. Just lately, Akt has been shown to be phosphorylated on tyrosine in COS cells handled with pervanadate , serum , or insulin like growth component . This tyrosine phosphorylation was necessary for total activation of Akt by pervanadate and IGF . When tyrosine was replaced by a phenylalanine, a lower in pervanadate and IGF stimulated Akt activation was observed . Thus, tyrosine phosphorylation dephosphorylation can be a feasible mechanism by which cell density may possibly regulate Akt activation.
We have now nevertheless to check this possibility. High density may perhaps regulate Akt activation by expanding serine threonine dephosphorylation. selleckchem original site Phosphatase A inhibits Akt activation by dephosphorylating each phosphothreonine from the Akt activation loop and phosphoserine in its C terminus . Potential experiments will be wanted to test this prospective mechanism. Other research assistance our conclusion that Akt activation, rather than Erk activation, plays a critical mitogenic function for breast cancer cell lines . Employing synthetic inhibitors within the Erk pathway, PD, and also the PI kinase Akt pathway, LY, Dufourny et al. showed that IGF mediated division in MCF cell cultures was dependent on PI kinase Akt activation and independent of Erk activation. In a separate examine, Busse et. al. applied a quinazoline inhibitor with the EGFR kinase in MDA breast carcinoma cells to induce growth arrest. This consequence might be reproduced by blocking the PI kinase Akt pathway, but growth arrest didn’t take place if only the Erk pathway was blocked .
These research, penlac collectively with ours, argue to get a essential purpose of Akt, not Erk , from the regulation of cell cycle progression of breast epithelial cells. Our data argue that a sustained EGF dependent Akt activation is needed for low density cells to divide and are in agreement with other scientific studies linking sustained Akt activation to regulation of proliferation. Sustained a thrombin induced Akt activation in Chinese hamster embryonic fibroblasts was demanded for DNA synthesis , and sustained activation of Akt was required for proliferation of pancreatic h cells . If Akt was only transiently activated, proliferation was not observed . How does suppression of Akt activation in large density cells cause development arrest?