Journal Article

AFAP1 Is a Novel Downstream Mediator of TGF- square 1 for CCN2 Induction in Osteoblasts: e0136712

Planey, Sonia L, Arnott, John A, Silverstein, Rachel, Geisinger, Max T, Corkill, Holly, Cunnick, Jess M, Cho, Youngjin, Martinkovich, Stephen

2015

Overview

Background CCN2 acts as an anabolic growth factor to regulate osteoblast differentiation and function. CCN2 is induced by TGF-[Beta]1 and acts as a mediator of TGF-[Beta]1 induced matrix production in osteoblasts and Src is required for CCN2 induction by TGF-[Beta]1; however, the molecular mechanisms that control CCN2 induction in osteoblasts are poorly understood. AFAP1 binds activated forms of Src and can direct the activation of Src in certain cell types, however a role for AFAP1 downstream of TGF-[Beta]1 or in osteoblats is undefined. In this study, we investigated the role of AFAP1 for CCN2 induction by TGF-[Beta]1 in primary osteoblasts. Results We demonstrated that AFAP1 expression in osteoblasts occurs in a biphasic pattern with maximal expression levels occurring during osteoblast proliferation (~day 3), reduced expression during matrix production/maturation (~day 14-21), an a further increase in expression during mineralization (~day 21). AFAP1 expression is induced by TGF-[Beta]1 treatment in osteoblasts during days 7, 14 and 21. In osteoblasts, AFAP1 binds to Src and is required for Src activation by TGF-[Beta]1 and CCN2 promoter activity and protein induction by TGF-[Beta]1 treatment was impaired using AFAP1 siRNA, indicating the requirement of AFAP1 for CCN2 induction by TGF-[Beta]1. We also demonstrated that TGF-[Beta]1 induction of extracellular matrix protein collagen XIIa occurs in an AFAP1 dependent fashion. Conclusions This study demonstrates that AFAP1 is an essential downstream signaling component of TGF-[Beta]1 for Src activation, CCN2 induction and collagen XIIa in osteoblasts.