Varadaraj Archana, Jenkins Laura M, Singh Priyanka, Chanda Anindya, Snider John, Lee N Y, Amsalem-Zafran Ayelet R, Ehrlich Marcelo, Henis Yoav I, Mythreye Karthikeyan
Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208.
Department of Environmental Health Sciences, University of South Carolina, Columbia, SC 29201.
Mol Biol Cell. 2017 May 1;28(9):1195-1207. doi: 10.1091/mbc.E16-08-0601. Epub 2017 Mar 15.
Fibronectin (FN) is a critical regulator of extracellular matrix (ECM) remodeling through its availability and stepwise polymerization for fibrillogenesis. Availability of FN is regulated by its synthesis and turnover, and fibrillogenesis is a multistep, integrin-dependent process essential for cell migration, proliferation, and tissue function. Transforming growth factor β (TGF-β) is an established regulator of ECM remodeling via transcriptional control of ECM proteins. Here we show that TGF-β, through increased FN trafficking in a transcription- and SMAD-independent manner, is a direct and rapid inducer of the fibrillogenesis required for TGF-β-induced cell migration. Whereas TGF-β signaling is dispensable for rapid fibrillogenesis, stable interactions between the cytoplasmic domain of the type II TGF-β receptor (TβRII) and the FN receptor (α5β1 integrin) are required. We find that, in response to TGF-β, cell surface-internalized FN is not degraded by the lysosome but instead undergoes recycling and incorporation into fibrils, a process dependent on TβRII. These findings are the first to show direct use of trafficked and recycled FN for fibrillogenesis, with a striking role for TGF-β in this process. Given the significant physiological consequences associated with FN availability and polymerization, our findings provide new insights into the regulation of fibrillogenesis for cellular homeostasis.
纤连蛋白(FN)是细胞外基质(ECM)重塑的关键调节因子,通过其可利用性以及逐步聚合形成纤维来实现。FN的可利用性受其合成和周转的调节,而纤维形成是一个多步骤、整合素依赖性过程,对细胞迁移、增殖和组织功能至关重要。转化生长因子β(TGF-β)是通过对ECM蛋白的转录控制来调节ECM重塑的既定调节因子。在此,我们表明,TGF-β通过以转录和SMAD非依赖性方式增加FN的运输,是TGF-β诱导的细胞迁移所需纤维形成的直接且快速的诱导剂。虽然TGF-β信号传导对于快速纤维形成并非必需,但II型TGF-β受体(TβRII)的胞质结构域与FN受体(α5β1整合素)之间的稳定相互作用是必需的。我们发现,响应TGF-β时,细胞表面内化的FN不会被溶酶体降解,而是经历再循环并整合到纤维中,这一过程依赖于TβRII。这些发现首次表明直接利用运输和再循环的FN进行纤维形成,TGF-β在此过程中发挥了显著作用。鉴于与FN可利用性和聚合相关的重大生理后果,我们的发现为细胞内稳态的纤维形成调节提供了新的见解。