The mechanosensitive caveolar interactome identifies a nuclear transport pathway linked to caveolae and YAP

Abstract

Mechanical forces are constantly generated during organ, tissue and cellular function and development. Eukaryotic cells contain multiple mechanotransduction pathways allowing them to sense and transmit diverse physical stimuli, which results in adaptation and functional reprogramming. Caveolae are small invaginations of the plasma membrane, essential for cell mechanoresponse and mechanoadaptation. This thesis focuses on the obtention of the complete caveolar interactome in basal condition and upon mechanical stress through the assessment of the binding partners of all the caveolar core constituents in these situations. This proteomic analysis has allowed us to validate previously described interactions amongst caveolar core components, as well as to conclude that the interactomes of all the caveolar constituents are highly sensitive to mechanical stress, as well as cell-type dependent. Moreover, we focus on one of the main caveolar components: CAVIN1. Its interactome has allowed us to describe four new findings: (i) CAVIN1 is translocated into the nucleus by Importin-7 upon mechanical or oxidative stress; (ii) CAVIN1 is involved in nucleolar stability; iii) CAVIN1 associates with the C/D box ribonucleoprotein complex; and iv) the HR1 domain of CAVIN1 is essential for CAVIN1 cytoplasmic retention, CAVIN1 role in nucleolar stability and CAVIN1 binding to the C/D box ribonucleoprotein complex. Furthermore, we determine that nucleoli are mechanosensitive organelles. In parallel, we demonstrate that Importin-7 is a mechanoresponsive nuclear transport receptor, the first described NTR of this kind, that has the ability to translocate into the nucleus another mechano-regulated protein, YAP. Furthermore, the mechanoresponse of Importin-7 depends on YAP, that acts as a dominant cargo and determines the binding of Importin-7 to its other cargoes SMAD3 and ERK2. Thus, we conclude that YAP fine-tunes the TGFβ and ERK pathways through modulation of the binding of their effectors to the nuclear transport receptor Importin-7