Rap1A Regulates Osteoblastic Differentiation via the ERK and p38 Mediated Signaling.

Yougen Wu,Yinghua Li,Juan Zhou,Yunjiao Zhou,Gong Yang,Yang Hong,Yunqing Cui,Chi Zhang

doi:10.1371/journal.pone.0143777

Abstract

Rap1A is a member of small G proteins belonging to the Ras family. Recently, an integration of human genome-wide association studies (GWAS) and gene expression profiling study revealed that single-nucleotide polymorphisms (SNPs) within human Rap1A were strongly associated with narrow neck width in women. However, the regulatory role of Rap1A in osteoblasts remains to be elucidated. Here we report that Rap1A is a key regulator in osteoblast differentiation. Rap1A expression and activity were gradually enhanced during the induced differentiation of multipotent mesenchymal progenitor cells (C2C12) and preosteoblastic cells (MC3T3-E1). Knockdown of endogenous Rap1A significantly inhibited the osteogenic marker gene expression and matrix mineralization in cells with osteogenesis. In addition, knockdown of endogenous Rap1A suppressed the activation of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK), while overexpression of Rap1A accelerated osteoblast differentiation and enhanced the phosphorylation of ERK and p38. Taken together, our study suggests that Rap1A regulates osteoblast differentiation through modulating the ERK/p38 signaling.

Highlights

Osteoblast proliferation, differentiation and maturation are crucial events in new bone formation and bone quality [1]
Before evaluating the effect of Rap1A on osteoblastic differentiation, we examined the endogenous Rap1A expression in C2C12 cells and preosteoblastic MC3T3-E1 cells using Western blotting
We examined the expression pattern of Rap1A in MC3T3-E1 cells treated with ascorbic acid (AA) and β-glycerophosphate (β-GP) for osteoblast differentiation

Summary

Introduction

Osteoblast proliferation, differentiation and maturation are crucial events in new bone formation and bone quality [1]. Osteoblasts synthesize and secrete a variety of bone-specific marker proteins including the runt-related transcription factor 2 (Runx2), alkaline phosphatase (Alp), the collagen type I alpha 1 (Col1a1), osteocalcin (OCN), osteopontin (OPN), osterix and bone sialoprotein (BSP), which act as structural supports, and play vital roles in osteoblast maturation and biological function including cell interaction, communication, matrix deposition, and mineralization [2, 3]. Numerous studies have demonstrated that the MAPK/ERK/ p38/JNK pathway regulates both in vitro osteoblast differentiation and in vivo bone formation [7,8,9]. Rap1A is a member of small G proteins belonging to the Ras oncogene family functioning in numerous biological processes including cell proliferation, adhesion, spreading, migration and cancer progression [10]. These results suggest that Rap1A is an important regulator of osteoblast differentiation

Materials and Methods

Results

Discussion