Downregulation of erythropoietin receptor by overexpression of phospholipase C-gamma 1 is critical for decrease on focal adhesion in transformed cells

Abstract

Background Phospholipase C-gamma 1 (PLC-gamma 1) is known to play a critical role in cell adhesion and migration and is highly expressed in metastatic tumors. In the current study, we found that cells transformed by PLC-gamma 1 overexpression (PLC-gamma 1 cells) exhibited a marked decrease in expression of the Epo receptor (EpoR). Here, we assessed the role of EpoR-dependent signaling pathways in PLC-gamma 1-dependent regulation of cell adhesion and migration. Methods Expression and phosphorylation of EpoR and its functional role in PLC-gamma 1 cells were evaluated by immunoblot analysis or cell adhesion assay. The mechanism for PLC-gamma 1-induced EpoR downregulation was analyzed by blockage of proteosomal degradation with MG132. EpoR expression was also confirmed in colorectal cancer tissues in which PLC-gamma 1 was highly expressed. Results EpoR was present on rat fibroblasts, where it functionally active and capable of increasing cell adhesion and migratory activity. However, PLC-gamma 1 cells significantly decreased the Epo-dependent effects via ubiquitination-proteosomal degradation of EpoR. A marked decrease of EpoR expression was confirmed in colorectal cancer tissues that showed high-level of PLC-gamma 1 expression. Conclusion The Epo/EpoR complex plays a critical role in the adhesion and migration of rat fibroblasts, and its functional inactivation is associated with PLC-gamma 1-dependent reduction of cell-matrix adhesion and this also affects cell migration.