Integrin-mediated adhesions in regulation of cellular senescence

Abstract

Bioinformatic and functional data link integrin-mediated cell adhesion to cellular senescence; however, the significance of and molecular mechanisms behind these connections are unknown. We now report that the focal adhesion–localized βPAK-interacting exchange factor (βPIX)–G protein–coupled receptor kinase interacting protein (GIT) complex controls cellular senescence in vitro and in vivo. βPIX and GIT levels decline with age. βPIX knockdown induces cellular senescence, which was prevented by reexpression. Loss of βPIX induced calpain cleavage of the endocytic adapter amphiphysin 1 to suppress clathrin-mediated endocytosis (CME); direct competition of GIT1/2 for the calpain-binding site on paxillin mediates this effect. Decreased CME and thus integrin endocytosis induced abnormal integrin signaling, with elevated reactive oxygen species production. Blocking integrin signaling inhibited senescence in human fibroblasts and mouse lungs in vivo. These results reveal a central role for integrin signaling in cellular senescence, potentially identifying a new therapeutic direction.

Altered endocytosis in cellular senescence

“…Restoration of amphiphysin 1 rescued endocytic capacity in senescent cells ( Park et al, 2001 ), though its contribution to senescence was not established. A recent study found that the reduction in amphiphysin was due to its cleavage by calpain and that blocking this step inhibited senescence ( Shin et al, 2020 ). These results provided stronger support for reduced CME as a functionally important step in senescence.…”

“…This process also involves microtubule targeting ( Ezratty et al, 2005 ), integrin endocytosis ( Chao and Kunz, 2009 ; Ezratty et al, 2009 ) and calpain-mediated proteolysis of FA proteins ( Chan et al, 2010 ; Cortesio et al, 2011 ; Franco et al, 2004 ). Analysis of these proteins in senescent cells revealed a new link between these events ( Shin et al, 2020 ). First, to understand whether reduced βPIX expression contributes to the senescent phenotype, both loss-of-function and gain-of-function studies were performed.…”

“…First, to understand whether reduced βPIX expression contributes to the senescent phenotype, both loss-of-function and gain-of-function studies were performed. Silencing βPIX in both cultured human diploid fibroblasts and in mouse lung induced senescence; conversely, overexpressing βPIX attenuated age-dependent senescent characteristics ( Shin et al, 2020 ). GIT knockdown also induced senescence in cultured fibroblasts, though this was not confirmed in vivo ( Shin et al, 2020 ).…”

“…3 ). The highly elevated activity of FAK and Rac1 results in elevated ROS production through the NADPH oxidase complex, which is causally implicated in senescence ( Shin et al, 2020 ).…”

“…Cellular senescence is associated with downregulation of CME via several mechanisms. First, decreased expression of βPIX and GIT1 altered the assembly of protein complexes within the focal adhesions, resulting in calpain-mediated degradation of the key endocytic adapter amphiphysin 1 ( Shin et al, 2020 ) ( Fig. 1 right, ②).…”