Caveolae-associated proteins in cardiomyocytes: caveolin-2 expression and interactions with caveolin-3.

Caveolin-3 the muscle-specific caveolin isoform, acts like the more ubiquitously expressed caveolin-1 to sculpt caveolae, specialized membrane microdomains that serve as platforms to organize signal transduction pathways. Caveolin-2 is a structurally related isoform that alone does not drive caveolae biogenesis; rather, caveolin-2 cooperates with caveolin-1 to form caveolae in nonmuscle cells. Although caveolin-2 might be expected to interact in an fashion analogous to that of caveolin-3, it generally has not been detected in cardiomyocytes. This study shows that caveolin-2 and caveolin-3 are detected at low levels in ventricular myocardium and increase dramatically with age or when neonatal cardiomyocytes are placed in culture. In contrast, flotillins (caveolin functional homologs) are expressed at relatively constant levels in these preparations. In neonatal cardiac cultures, caveolin-2 and -3 expression is not influenced by thyroid hormone (a postnatal regulator of other cardiac gene products). The further evidence that caveolin-2 coimmunoprecipitates with caveolin-3 and floats with caveolin-3 by isopycnic centrifugation in cardiomyocyte cultures suggests that caveolin-2 may play a role in caveolae biogenesis and influence cardiac muscle physiology.