Mechanotransduction of matrix stiffness in regulation of focal adhesion size and number: reciprocal regulation of caveolin-1 and β1 integrin

Abstract

Focal adhesion (FA) assembly, mediated by integrin activation, responds to matrix stiffness; however, the underlying mechanisms are unclear. Here, we showed that β1 integrin and caveolin-1 (Cav1) levels were decreased with declining matrix stiffness. Soft matrix selectively downregulated β1 integrin by endocytosis and subsequent lysosomal degradation. Disruption of lipid rafts with methyl-β-cyclodextrin or nystatin, or knockdown of Cav1 by siRNA decreased cell spreading, FA assembly, and β1 integrin protein levels in cells cultured on stiff matrix. Overexpression of Cav1, particularly the phospho-mimetic mutant Cav1-Y14D, averted soft matrix-induced decreases in β1 integrin protein levels, cell spreading, and FA assembly in NMuMG cells. Interestingly, overexpression of an auto-clustering β1 integrin hindered soft matrix-induced reduction of Cav1 and cell spreading, which suggests a reciprocal regulation between β1 integrin and Cav1. Finally, co-expression of this auto-clustering β1 integrin and Cav1-Y14D synergistically enhanced cell spreading, and FA assembly in HEK293T cells cultured on either stiff ( > G Pa) or soft (0.2 kPa) matrices. Collectively, these results suggest that matrix stiffness governs the expression of β1 integrin and Cav1, which reciprocally control each other, and subsequently determine FA assembly and turnover.

Exogenous expression of caveolin‐1 is sufficient for hepatic stellate cell activation

“…Integrins communicate positional and mechanical signals from the ECM to the extracellular milieu, modulating important cell function such as adhesion, migration, and proliferation. β1 integrin and paxillin are adhesions proteins connected with Cav‐1 and ECM . To investigate if these proteins are involved in the aforementioned adhesion pattern, we evaluated their expression by measurement of IF in GRX and GRX EGFP‐Cav1 , seeking for the potential proteins colocalizations.…”

“…Mechanosensing is when cells transduce the mechanical proprieties to cells‐ECM and cell‐cell interactions through FA that are linked to actin fibers . Integrins are an important cell adhesion proteins that act in cell‐cell and cell‐ECM interactions, and are the first to be activated among FA proteins during wound healing responses . Indeed, β1 integrin protein increase is associated with the progression of fibrotic liver diseases .…”

“…43 Integrins are an important cell adhesion proteins that act in cell-cell and cell-ECM interactions, and are the first to be activated among FA proteins during wound healing responses. 3,40,43 Indeed, β1 integrin protein increase is associated with the progression of fibrotic liver diseases. 40 Cav-1 and β1 integrin have a strong association with adhesion proprieties and migration, remodeling actin cytoskeleton and stabilizing the focal adhesion kinase at FA.…”

“…β1 integrin and paxillin are adhesions proteins connected with Cav-1 and ECM. 39,40 To investigate if these proteins are involved in the aforementioned adhesion pattern, we evaluated their expression by measurement of IF in GRX and GRX EGFP-Cav1 , seeking for the potential proteins colocalizations. As expected, the IF of both proteins was increased in response to exogenous expression of Cav-1 ( Figure 4A and 4B).…”

The role of extracellular matrix stiffness in regulating cytoskeletal remodeling via vinculin in synthetic smooth muscle cells

“…[44] On a soft matrix, β1 integrin is downregulated through lysosomal degradation pathway. [45] Because vinculin in FAs engages cytoskeleton to ECM through integrin and is involved in cell spread and growth, a higher Vcl level on the soft matrix could be attributed to genetic compensation mechanism. [46] In fact, a recent study shows that the transcriptional program in endothelial cells induced by stiffness is regulated by GATA Binding Protein 2 (GATA2) transcription factor, and that genes involved in cell-ECM adhesion are upregulated on soft ECM (0.2 kPa).…”