Mechanical tension is an ever-present physiological stimulus essential for the development and homeostasis of locomotory, cardiovascular, respiratory, and urogenital systems. Tension sensing contributes to stem cell differentiation, immune cell recruitment, and tumorigenesis. Yet, how mechanical signals are transduced inside cells remains poorly understood. Here, we identify chaperone-assisted selective autophagy (CASA) as a tension-induced autophagy pathway essential for mechanotransduction in muscle and immune cells. The CASA complex, comprised of the molecular chaperones Hsc70 and HspB8 and the cochaperone BAG3, senses the mechanical unfolding of the actin-crosslinking protein filamin. Together with the chaperone-associated ubiquitin ligase CHIP, the complex initiates the ubiquitin-dependent autophagic sorting of damaged filamin to lysosomes for degradation. Autophagosome formation during CASA depends on an interaction of BAG3 with synaptopodin-2 (SYNPO2). This interaction is mediated by the BAG3 WW domain and facilitates cooperation with an autophagosome membrane fusion complex. BAG3 also utilizes its WW domain to engage in YAP/TAZ signaling. Via this pathway, BAG3 stimulates filamin transcription to maintain actin anchoring and crosslinking under mechanical tension. By integrating tension sensing, autophagosome formation, and transcription regulation during mechanotransduction, the CASA machinery ensures tissue homeostasis and regulates fundamental cellular processes such as adhesion, migration, and proliferation.

CD81 (TAPA-1) is a member of the widely expressed and evolutionary conserved tetraspanin family that forms complexes with a variety of other cell surface receptors and facilitates hepatitis C virus entry. Here, we show that CD81 is specifically required for the formation of lamellipodia in migrating dendritic cells (DCs). Mouse CD81 ؊/؊ DCs, or murine and human CD81 RNA interference knockdown DCs lacked the ability to form actin protrusions, thereby impairing their motility dramatically. Moreover, we observed a selective loss of Rac1 activity in the absence of CD81, the latter of which is exclusively required for integrin-dependent migration on 2-dimensional substrates. Neither integrin affinity for substrate nor the size of basal integrin clusters was affected by CD81 deficiency in adherent DCs. However, the use of total internal reflection fluorescence microscopy revealed an accumulation of integrin clusters above the basal layer in CD81 knockdown cells. Furthermore, ␤1-or ␤2-integrins, actin, and Rac are strongly colocalized at the leading edge of DCs, but the very fronts of these cells protrude CD81-containing membranes that project outward from the actin-integrin area. Taken together, these data suggest a thus far unappreciated role for CD81 in the mobilization of preformed integrin clusters into the leading edge of migratory DCs on 2-dimensional

Leukocyte trafficking is crucial to facilitate efficient immune responses. Here, we report that the large GTPase dynamin2, which is generally considered to have a key role in endocytosis and membrane remodeling, is an essential regulator of integrin-dependent human T lymphocyte adhesion and migration. Chemical inhibition or knockdown of dynamin2 expression significantly reduced integrin-dependent T cell adhesion in vitro. This phenotype was not observed when T cells were treated with various chemical inhibitors which abrogate endocytosis or actin polymerization. We furthermore detected dynamin2 in signaling complexes and propose that it controls T cell adhesion via FAK/Pyk2- and RapGEF1-mediated Rap1 activation. In addition, the dynamin2 inhibitor-induced reduction of lymphocyte adhesion can be rescued by Rap1a overexpression. We demonstrate that the dynamin2 effect on T cell adhesion does not involve integrin affinity regulation but instead relies on its ability to modulate integrin valency. Taken together, we suggest a previously unidentified role of dynamin2 in the regulation of integrin-mediated lymphocyte adhesion via a Rap1 signaling pathway.

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