Phosphorylation of Erf in Vascular Smooth Muscle Cells: Role of Erk-1/2 and Intracellular Calcium

Ets-2 repressor factor (Erf) is a relatively little explored member of the Ets (E26 transformation specific)-domain transcription factor family. It is a phosphoprotein consisting of 548 amino acids, with a molecular weight of 75 kDa. Unphosphorylated Erf is a transcriptional repressor and induces cell cycle arrest in the G0/G1-phase, thus preventing cellular growth and proliferation. To present it is neither known whether endogenous Erf is expressed in vascular smooth muscle cells (VSMCs) nor how the phosphorylation of Erf is regulated in VSMCs. For this purpose A-10 embryonic rat thoracic aorta VSMC were treated with the mitogenic stimuli platelet-derived growth factor (PDGF) or low-density lipoprotein (LDL), and phosphorylation of Erf was analyzed by Western blot. Furthermore, to determine whether phosphorylation of Erf is dependent on extracellular signal-regulated kinase (Erk)-1/2, specific Mek-1/2 inhibitors U0126 and PD98059 were used. Additionally, phosphorylation of Erk-1/2 and Erf after treatment with the intracellular calcium chelator BAPTA/AM, either alone or in combination with PDGF, was investigated. The results show that Erf is expressed endogenously in VSMCs and phosphorylated by Erk-1/2 upon mitogenic stimulation. Furthermore, a decrease in intracellular calcium concentration, alone or in combination with a mitogenic stimulus, leads to increased phosphorylation of Erk-1/2 and Erf. These findings suggest that in VSMCs Erf phosphorylation is induced by pro-atherogenic agents (PDGF or LDL) via the activation of Erk-1/2 and regulation of Erf phosphorylation additionally involves levels of intracellular calcium. Thus, Erf could play an important role in VSMC proliferation, dedifferentiation and migration, and contribute towards the development of vascular remodelling diseases. Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: http://doi.org/10.5167/uzh-67727 Originally published at: Verta-Nabholz, Stephanie Jane. Phosphorylation of Erf in Vascular Smooth Muscle Cells: Role of Erk-1/2 and Intracellular Calcium. 2011, University of Zurich, Faculty of Medicine.