The role of splicing factor PTBP1 in mechanotransduction

Mechanical cues play a vital role in numerous biological processes, including embryonic development, aging, cellular homeostasis, and disease progression. Cells sense and convert these mechanical signals into biochemical responses that regulate cell behaviours like proliferation and migration through a process known as mechanotransduction. In this study, we present a comprehensive, large-scale approach to identify proteins with a mechanosensitive nuclear localisation and therefore a potential role in mechanotransduction. Our screening method is based on inducing acute changes in cellular traction forces, combined with in situ biotinylation of nuclear proteins, followed by mass spectrometry analysis. This screen approach identified among other proteins the splicing factor PTBP1 as a protein with mechanosensitive nuclear localisation, and we show that its nuclear abundance can be regulated by mechanical cues such as cell density, cell size, and extracellular matrix (ECM) stiffness. Moreover, we demonstrate that PTBP1 is essential for ECM stiffness-driven mesenchymal stem cell differentiation into osteoblasts, as well as for epithelial cell spreading and stiffness-induced proliferation. Furthermore, we show that PTBP1 mediates mechanosensitive alternative splicing of the endocytic adapter protein Numb, and that this splicing event affects the membrane trafficking of the mechanosensor integrin beta1 and is critical for matrix stiffness-induced stem cell differentiation and epithelial cell proliferation and cell spreading. Our findings support the emerging concept that alternative splicing plays a crucial role in mechanotransduction, offering new mechanistic insights into how matrix stiffness influences cellular mechanoresponses.