oa Regulation Of Erk Phosphorylation In Calreticulin Knockout Mouse Embryonic Fibroblast Cells

Extracellular signal regulated kinase (ERK1/2) is a member of the mitogen-activated protein kinase pathway (MAPK). ERK1/2 has a wide variety of functions including cell proliferation, differentiation, and migration to name a few. Thus alteration in the ERK1/2 pathway can result in different pathologies such as cancer, cardiovascular diseases and diabetes. ERK MAP kinase is activated through binding of extracellular growth factors such as PDGF and EGF to their respective receptors. Calreticulin (CRT) is an endoplasmic reticulum (ER) chaperone that aids in the protein folding and maturation. It also plays a role in the ER quality control process. Our lab previously illustrated that CRT knockout cells compensate for ER stress by activating ER associated protein degradation. We also demonstrated that loss of CRT increased cellular resistance to apoptosis due to activation of Akt pathway. Activation of ERK signaling pathway was shown to protect against ER-induced cell death. To date little is known about the role of CRT in the ERK pathway. Thus the objective of our study was to examine changes in ERK1/2 kinase and the growth factor receptors in CRT knockout cells. Western blot analysis with anti-ERK1/2 antibody illustrated no significant change in the ERK1/2 protein level in crt−/− as compared to wt cells. However, the basal p-ERK1/2 was significantly higher in the crt−/− as compared to wt cells after overnight starvation. Interestingly, FBS stimulation resulted in increased phosphorylation of ERK1/2 to the same level in both cell lines. On the other hand 10 min EGF stimulation resulted in a significantly higher p-ERK1/2 in CRT knockout cells as compared to the wt cells. Overall, these data illustrate that loss of CRT function results in increased ERK phosphorylation and might contribute to the observed increased resistance to apoptosis and cell proliferation.