Mutational analysis of caveolin‐induced vesicle formation

Authors:
Publisher website
Google Scholar
Abstract
Caveolae are vesicular organelles with a characteristic uniform diameter in the range of 50–100 nm. Although recombinant expression of caveolin‐1 is sufficient to drive caveolae formation, it remains unknown what controls the uniform diameter of these organelles. One hypothesis is that specific caveolin‐caveolin interactions regulate the size of caveolae, as caveolin‐1 undergoes two stages of self‐oligomerization. To test this hypothesis directly, we have created two caveolin‐1 deletion mutants that lack regions of caveolin‐1 that are involved in directing the self‐assembly of caveolin‐1 oligomers. More specifically, Cav‐1 Δ61–100 lacks a region of the N‐terminal domain that directs the formation of high molecular mass caveolin‐1 homo‐oligomers, while Cav‐1 ΔC lacks a complete C‐terminal domain that is required to allow caveolin homo‐oligomers to interact with each other, forming a caveolin network. It is important to note that these two mutants retain an intact transmembrane domain. Our current results show that although Cav‐1 Δ61–100 and Cav‐1 ΔC are competent to drive vesicle formation, these vesicles vary widely in their size and shape with diameters up to 500–1000 nm. In addition, caveolin‐induced vesicle formation appears to be isoform‐specific. Recombinant expression of caveolin‐2 under the same conditions failed to drive the formation of vesicles, while caveolin‐3 expression yielded caveolae‐sized vesicles. These results are consistent with the previous observation that in transformed NIH 3T3 cells that lack caveolin‐1 expression, but continue to express caveolin‐2, no morphologically distinguishable caveolae are observed. In addition, as caveolin‐2 alone exists mainly as a monomer or homo‐dimer, while caveolins 1 and 3 exist as high molecular mass homo‐oligomers, our results are consistent with the idea that the formation of high molecular mass oligomers of caveolin are required to regulate the formation of uniform caveolae‐sized vesicles. In direct support of this notion, regulated induction of caveolin‐1 expression in transformed NIH 3T3 cells was sufficient to recruit caveolin‐2 to caveolae membranes. The ability of caveolin‐1 to recruit caveolin‐2 most likely occurs through a direct interaction between caveolins 1 and 2, as caveolins 1 and 2 are normally co‐expressed and interact with each other to form high molecular mass hetero‐oligomers containing both caveolins 1 and 2.

This publication has 50 references indexed in Scilit: