Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC348
Caveolin-1 knockout reduces the expression of cavin-1, but not flotillins, in murine smooth muscle.
J. Martin1, N. Hausman2, C. Austin2, M. J. Taggart1
1. Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom. 2. Cardiovascular Research Group, Manchester University, Manchester, United Kingdom.
Caveolae are associated with the orchestration of multiple signalling pathways in most mammalian cells including smooth muscle. However, there is considerable debate as to which proteins are critical components of caveolae formation, integrity and function. Caveolin-1 has long been known to serve these functions. Recently, expression of cavin-1 (also known as PTRF) in heterologous cells has been found to induce formation of caveolae in a caveolin-1-dependent manner . Furthermore, cavin-1 knockout mice show much reduced levels of caveolin-1 and no appearance of caveolae in a number of tissues . However, flotillins-1 and -2, proteins usually found not to co-localise with caveolins, have been reported to induce the formation of Ω-shaped plasmalemmal invaginations, i.e. features morphologically similar to caveolae, in HeLa cells . There is little information on the inter-dependence, or otherwise, of these proteins in smooth muscle. Therefore, in the present study we examined whether the expressions of cavin-1, flotillin-1 or flotillin-2 proteins were altered in smooth muscle tissue isolated from caveolin-1 knockout mice. 3 month old Wild type (WT) and caveolin-1 knockout (KO) mice were killed by cervical dislocation and ileal smooth muscle harvested for western blotting and quantification of protein expression by densitometry. All tissues from WT mice were positive for caveolin-1, cavin-1 and flotillins. Tissue from KO mice were, as expected, devoid of caveolin-1 (and caveolae as examined by electron microscopy) but they also showed significantly reduced levels of cavin-1 (cavin-1 expression was 32.3 + 10.1 a.u. versus 0.88 + 0.39 a.u. in WT and KO respectively, mean + sem, n=6, P < 0.05, students unpaired t-test on log transformed data). In contrast, neither flotillin-1 (WT 24.3 + 3.10 a.u. versus KO 19.8 + 3.22 a.u.) nor flotillin-2 (WT 47.3 + 1.63 a.u. versus KO 39.8 + 3.55 a.u.) protein expression was significantly altered by caveolin-1 KO. We conclude that caveolin-1 ablation concomitantly reduces the expression of cavin-1, but not flotillin-1 or -2, in murine smooth muscle. This supports the possibility that the reciprocal regulation of caveolin-1 and cavin-1 proteins may be an important feature of caveolae function in smooth muscle.
Where applicable, experiments conform with Society ethical requirements