CCN2 Increases TGF- Receptor Type II Expression in Vascular Smooth Muscle Cells: Essential Role of CCN2 in the TGF- Pathway Regulation

Abstract

The cellular communication network factor 2 (CCN2/CTGF) has been traditionally described as a mediator of the fibrotic responses induced by other factors including the transforming growth factor (TGF- ). However, several studies have defined a direct role of CCN2 acting as a growth factor inducing oxidative and proinflammatory responses. The presence of CCN2 and TGF- together in the cellular context has been described as a requisite to induce a persistent fibrotic response, but the precise mechanisms implicated in this relation are not described yet. Considering the main role of TGF- receptors (T R) in the TGF- pathway activation, our aim was to investigate the effects of CCN2 in the regulation of T RI and T RII levels in vascular smooth muscle cells (VSMCs). While no differences were observed in T RI levels, an increase in T RII expression at both gene and protein level were found 48 h after stimulation with the C-terminal fragment of CCN2 (CCN2(IV)). Cell pretreatment with a T RI inhibitor did not modify T RII increment induced by CCN2(VI), demonstrating a TGF- -independent response. Secondly, CCN2(IV) rapidly activated the SMAD pathway in VSMCs, this being crucial in the upregulation of T RII since the preincubation with an SMAD3 inhibitor prevented it. Similarly, pretreatment with the epidermal growth factor receptor (EGFR) inhibitor erlotinib abolished T RII upregulation, indicating the participation of this receptor in the observed responses. Our findings suggest a direct role of CCN2 maintaining the TGF- pathway activation by increasing T RII expression in an EGFR-SMAD dependent manner activation.