These effects produce strong evidence that EGF induces tyrosine phosphorylation of EGFR and Jak2 through car phosphorylation of these kinases, as well as demonstce that the proton efflux is mediated by NHE 1 is the fact that it will be dependent upon extracellular sodium, inhibited by MIA, dependent on CaM action, and connected with elevated binding of CaM to NHE one. The exact mechanism as a result of which Jak2 activates NHE 1 hasn’t been totally elucidated. We propose that Jak2 tyrosine phosphorylates CaM, therefore growing its affinity for NHE 1. This would result in improved binding of CaM to NHE one. A number of kinases happen to be shown to phosphorylate CaM on serine, threonine and tyrosine residues , and to alter the exercise of CaM with reference to exact CaM targets . In that regard, our group has not too long ago demonstrated that CaM is straight tyrosine phosphorylated by purified Jak2 . Thus, Jak2 nearly absolutely phosphorylates CaM on a single or each of the tyrosine residues in the CaM sequence, Tyr 99 and Tyr 138. Dependant on the crystal framework of CaM, Tyr 99 is the even more possible target for phosphorylation in that Tyr 99 is located inside the third Ca2 binding domain, and it is relatively much more exposed than is Tyr 138 .
Then again, Jak2 induced tyrosine phosphorylation of CaM appears to get vital or critical, but not adequate to completely activate NHE 1, considering that EGFR tyrosine kinase activity also is required. Without a doubt, the effectiveness of AG1478 to block NHE 1 activation suggests that EGFR tyrosine kinase action also is essential for CaM to bind to NHE 1 and also to activate it. It will need to be noted that we’ve got not formally examined the idea that CaM chemical library binding to NHE one induces a conformational alter that effects in activation of NHE 1. Nonetheless, this idea is intuitively pleasing, and has been supported by experimental proof within the form of mutation research by , and by remedy phase spectroscopy research with the interaction amongst CaM plus the large regulatory intracellular carboxyl terminus of NHE 1 by Fliegel?s group .
It is vital to elaborate on our findings the EGFR kinase inhibitor AG1478 didn’t decrease the quantity of Jak2 and CaM in phosphotyrosine immunoprecipitates , which suggests that there is a further aspect that Sodium valproate permits EGF to manage tyrosine phosphorylation of CaM independent of EGFR kinase exercise. This choosing is supported by earlier reports that suggest that some EGF mediated signals such because the JAK STAT pathway are independent of EGFR kinase activity . Two groups demonstrated that AG1478 independent results of EGF might be mediated by ErbB2 , potentially via oligomerization with ErbB1 EGFR . It will be unlikely that this mechanism can account for our findings in that we detected small to no Neu HER2 mRNA in differentiated podocytes .