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Caveolin-1 and membrane domain regulation of focal adhesions and tumor cell migration Meng, Fanrui

Abstract

Caveolin-1 (Cav1), a key protein component of cell surface invagination caveolae and a major substrate of Src kinase, has been shown to be associated with cancer malignancy. Galectin-3 (Gal3), a galactose-specific lectin, forms oligomers and crosslinks N-glycans on cell surface to form the galectin lattice. Gal3 and Cav1 function together to regulate focal adhesion dynamics and tumor cell migration. In this thesis we hypothesize that the galectin lattice, Cav1 membrane domain organization (caveolae, Cav1 scaffolds) and Cav1 molecular motifs (tyrosine 14 phosphorylation (pY14), the caveolin scaffolding domain (CSD)) are all involved in Cav1 promotion of focal adhesion dynamics and tumor cell motility. Firstly, we found a synergistic expression of Cav1 and Gal3 in malignant thyroid cancer cells, which was required for focal adhesion kinase (FAK) stabilization in focal adhesions (a measure of focal adhesion dynamics), RhoA activation and cell migration. Co-overexpression of Cav1 and Gal3, but not either alone, in an anaplastic thyroid cancer cell line stabilized FAK within focal adhesions. Therefore, co-function of Cav1 and Gal3 is required to promote focal adhesion dynamics and cell migration in thyroid cancer. Next we found that overexpression of PTRF/cavin-1 in PC3 prostate cancer cells, and consequent formation of caveolae, decreased cell motility by destabilizing FAK in focal adhesions. The impaired focal adhesion stabilization of FAK in PTRF/cavin-1-expressing PC3 cells was rescued by exogenous Gal3 in a Cav1-dependent manner. Hence the alteration of Cav1 microdomains by PTRF/cavin-1 overexpression decreases cell motility through affecting focal adhesion dynamics, which is overridden by reinforced Cav1-Gal3/galectin lattice co-function. Finally, using Cav1-positive but tyrosine 14-phosphorylated Cav1 (pY14Cav1)-negative DU145 prostate cancer cells, various Cav1 Y14 and CSD mutants and a CSD mimicking/competing peptide, we found a CSD-dependent pY14Cav1 regulation of focal adhesion dynamics and cell motility. Vinculin, a mechano-sensor at focal adhesions that was previously shown to recruit and stabilize other focal adhesion components, preferentially bound pY14Cav1 and was stabilized in focal adhesions by pY14Cav1 in a CSD-dependent manner. Vinculin tension was induced by pY14Cav1 in a CSD-dependent manner. Therefore, a novel interplay between pY14 and the CSD of Cav1 regulates focal adhesion dynamics and tension favouring cell migration.

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