Functional Changes of Actin-Binding Proteins for Human Umbilical CD-105 Positive Stromal Cell Proliferation and Differentiation

Abstract

Human umbilical Wharton's jelly cells (WJCs) possess the capacity of self-renewal and differentiation of mesenchymal stromal cells. In this study, human umbilical CD105-positive WJCs were cultured to investigate the functional roles of actin binding proteins in cell proliferation and adipogenic differentiation. Genistein, a tyrosine protein kinase inhibitor, lowered intracellular Ca2+ such as to attenuate cell proliferation and DNA synthesis through the β-catenin/ cyclin D1 pathway in the cells. Immunofluorescence confocal scanning microscopy indicated that changes in the subcellular distribution of tropomyosin (Tm), in which the diffuse cytosolic staining was shifted to show colocalization of Tm with actin stress fibers. Genistein treatment of cells also induced increases in the colocalization of caldesmon (CaD) and stress fibers. In contrast, genistein increased accumulation of the actin-nucleating protein formin-2 (FMN-2) and profilin in the peri-nuclear area. Silencing of FMN-2 by siRNA raised intracellular Ca2+ and rendered genistein resistance in decreasing intracellular Ca2+ in the cells. To define how actin filament assembly is regulated in the adipogenic differentiation, we determined functional changes in gene expression of actin binding proteins associated with morphological transformation in adipogenesis-induced WJCs. Adipogenic differentiation, as indicated by elevating expression of PPAR-γ mRNA, caused changes in β-actin mRNA expression and protein level. Gelsolin, an actin filament severing protein, also displayed a biphasic change of mRNA expression and protein level in the differentiation. During adiopogenesis mRNA expression levels for FMN-2 and Tm-1 were declined significantly, but no changes for Tm-2 and Tm-4. Taken together, our study resulted in the novel finding that actin-binding proteins act by modulating actin filament assembly for the proliferation and differentiation in human WJCs.