The biology of caveolae: lessons from caveolin knockout mice and implications for human disease

Caveolae, plasma membrane invaginations that function membrane organizing facilities, are present in most cell sorts, however are enriched in adipocytes, endothelial cells, and myocytes. Three members of the caveolinfamily (Cav-1, -2, and -3) are important for the formation of caveolae. Specialized motifs within the caveolin proteins perform to recruit lipids and proteins to caveolae for participation in intracellular trafficking of mobile parts and operation in sign transduction.

Mutations within the gene encoding CAV-1 are related to the event and development of breast cancers, whereas mutations within the CAV-3 gene lead to Rippling Muscle Disease and a type of Limb-Girdle Muscular Dystrophy.

The generation of caveolin-null mice has confirmed the important position of these proteins in caveolae biogenesis and within the pathophysiology of numerous tissues. Caveolin-null mice present new animal fashions for finding out the pathogenesis of a quantity of human ailments, together with most cancers, diabetes, atherosclerosis, restrictive lung disease and pulmonary fibrosis, cardiomyopathy, muscular dystrophy, and bladder dysfunction.

The caveolingenefamily consists of caveolins 1, 2, and 3. Caveolins 1 and 2 are co-expressed in lots of cell sorts, reminiscent of endothelial cells, fibroblasts, easy muscle cells and adipocytes, the place they type a heteroligomeric advanced. In distinction, the expression of caveolin-Three is muscle-specific.

Thus, the expression of caveolin-1 is required for caveolae formation in non-muscle cells, whereas the expression of caveolin-Three drives caveolae formation in striated muscle cell sorts (cardiac and skeletal). To create a very caveolae-deficient mouse, we interbred Cav-1 null mice and Cav-Three null mice to genefee Cav-1/Cav-Three double-knockout (Cav-1/Three dKO) mice.

Here, we report that Cav-1/Three dKO mice are viable and fertile, even supposing they lack morphologically identifiable caveolae in endothelia, adipocytes, easy muscle cells, skeletal muscle fibers, and cardiac myocytes. We additionally present that these mice are poor in all three caveolingene merchandise, as caveolin-2 is unstable within the absence of caveolin-1. Interestingly, Cav-1/Three dKO mice develop a extreme cardiomyopathy.

At 2 months of age, evaluation of Cav-1/Three dKO hearts by way of gated magnetic resonance imaging reveals a dramatic improve in left ventricular wall thickness, as in contrast with Cav-1-KO, Cav-Three KO, and wild-type mice. Further practical evaluation of Cav-1/Three dKO hearts by way of transthoracic echocardiography demonstrates hypertrophy and dilation of the left ventricle, with a big lower in fractional shortening.

As predicted, Northern evaluation of RNA derived from the left ventricle of Cav-1/Three dKO mice exhibits a dramatic up-regulation of the atrial natriuretic issue message, a well-established biochemical marker of cardiac hypertrophy. Finally, histological evaluation of Cav-1/Three dKO hearts reveals hypertrophy, disorganization, and degeneration of the cardiac myocytes, in addition to continual interstitial fibrosis and irritation. Thus, twin ablation of each Cav-1 and Cav-3 genes in mice results in a pleiotropic defect in caveolae formation and extreme cardiomyopathy.

Tumors of the Ewing’s sarcoma household (ESFT), reminiscent of Ewing’s sarcoma (EWS) and primitive neuroectodermal tumors (PNET), are extremely aggressive malignancies predominantly affecting kids and younger adults. ESFT categorical chimeric transcription elements encoded by hybrid genes fusing the EWS gene with a number of ETS genes, mostly FLI-1. EWS/FLI-1 proteins are accountable for the malignant phenotype of ESFT, however solely few of their transcriptional targets are identified.

Using antisense and brief hairpin RNA-mediated gene expression knockdown, array analyses, chromatin immunoprecipitation strategies, and reexpression research, we present that caveolin-1 (CAV1) is a brand new direct goal of EWS/FLI-1 that’s overexpressed in ESFT cell traces and tumor specimens and is important for ESFT tumorigenesis. CAV1 knockdown led to up-regulation of Snail and the concomitant loss of E-cadherin expression.

Consistently, loss of CAV1 expression inhibited the anchorage-independent progress of EWS cells and markedly lowered the expansion of EWS cell-derived tumors in nude mice xenografts, indicating that CAV1 promotes the malignant phenotype in EWS carcinogenesis. Reexpression of CAV1 or E-cadherin in CAV1 knockdown EWS cells rescued the oncogenic phenotype of the unique EWS cells, displaying that the CAV1/Snail/E-cadherin pathway performs a central position within the expression of the oncogenic transformation capabilities of EWS/FLI-1.

Overall, these information determine CAV1 as a key determinant of the tumorigenicity of ESFT and indicate that focusing on CAV1 might enable the event of new molecular therapeutic methods for ESFT sufferers.

WNT signaling in stem cell biology and regenerative drugs

Caveolae are vesicular organelles that signify a subcompartment of the plasma membrane. Caveolins and flotillins are two households of mammalian caveolae-associated integral membrane proteins. However, it stays unknown whether or not flotillins work together with caveolin proteins to type a steady caveolar advanced or if expression of flotillins can drive vesicle formation.

Here, we study the cell kind and tissue-specific expression of the flotillin genefamily. For this objective, we generated a novel monoclonal antibody probe that acknowledges solely flotillin-1. A survey of cell and tissue sorts demonstrates that flotillins 1 and 2 have a complementary tissue distribution.

At the mobile degree, flotillin-2 was ubiquitously expressed, whereas flotillin-1 was most ample in A498 kidney cells, muscle cell traces, and fibroblasts. Using three completely different fashions of mobile differentiation, we subsequent examined the expression of flotillins 1 and 2. Taken collectively, our information recommend that the expression ranges of flotillins 1 and 2 are independently regulated and doesn’t strictly correlate with identified expression patterns of caveolinfamily members.

However, when caveolins and flotillins are co-expressed inside the similar cell, as in A498 cells, they type a steady hetero-oligomeric “caveolar advanced.” In help of these observations, we present that heterologous expression of murine flotillin-1 in Sf21 insect cells utilizing baculovirus-based vectors is adequate to drive the formation of caveolae-like vesicles. These outcomes recommend that flotillins might take part functionally within the formation of caveolae or caveolae-like vesicles in vivo.

Thus, flotillin-1 represents a brand new integral membrane protein marker for the marginally bigger caveolae-related domains (50-200 nm) which might be noticed in cell sorts that fail to precise caveolin-1. As a consequence of these findings, we suggest the time period “cavatellins” be used (as a substitute of flotillins) to explain this genefamily.