MmuEX0015299 @ mm9

The authors expressed each of the four dynamin 2 isoforms (aa, ab, ba, and bb) as either wild-type proteins or GTPase-defective mutants. When expressed as enhanced green fluorescent protein (EGFP) fusions, these isoforms were found to have overlapping subcellular distributions being localized throughout the cell cytoplasm, on punctate vesicles and in a perinuclear compartment. This distribution was qualitatively similar to that of endogenous dynamin 2 and overlapped with GLUT-4 in the basal state. Expression of wild-type dynamin 2 isoforms had no effect on the basal or insulin-stimulated distribution of GLUT-4; however, expression of the dominant-interfering dynamin 2 mutants similarly inhibited GLUT-4 endocytosis. These data demonstrate that dynamin 2 is required for GLUT-4 endocytosis in 3T3L1 adipocytes and suggest that, relative to GLUT-4 trafficking, the dynamin 2 splice variants have overlapping functions and are probably not responsible for mediating distinct GLUT-4 budding events.

In vitro binding studies using two Dyn2 spliced forms (aa and bb) and Cav1 peptides immobilized on paper identify specific domains of Cav1 that bind Dyn2. Interestingly, these Cav1-binding domains differ markedly between two spliced variant forms of Dyn2. In a hepatocyte cell line, the K44A-isoform 1 inhibits caveolae-dependent internalization, but not the other K44A mutant isoforms. Isoform 1 (aa): Includes MmuEX0015299+MmuEX0015304. Isoform 2 (ba): MmuEX0015305+MmuEX0015304. Isoform 3 (ab): MmuEX0015299. Isoform 4 (bb): MmuEX0015305.

In a cultured rat epithelial cell line (clone 9), the K44A mutants of isoforms 2 and 4 (with exon 10bis; MmuEX0015305) are able to inhibit fluid-phase endocytosis, whereas the mutant forms of isoforms 1 and 3 (with exon 10; MmuEX0015299) do not, and are also more potent inhibitors of clathrin-mediated endocytosis.

MUTEX. All Dnm2 isoforms localize to clathrin-coated pits at the plasma membrane but only DNM2ba and DNM2bb (i.e. including MmuEX0015299, instead of MmuEX0015305) localize to the Golgi. All isoforms rescue the endocytosis defects in Dyn2-depleted cells, but DNM2ba and DNM2bb were more effective than the DNM2aa and DNM2ab variants with regard to rescuing the export of the neutrophin receptor p75 from the trans-Golgi network. NOTE: the second a/b correspond to inclusion/exclusion of MIC MmuEX0015304.

[Review conclusion]. Altogether, these data suggest a preferential involvement of isoforms 1 and 3 in clathrin and caveolae-dependent endocytosis, whereas isoforms 2 and 4 participate in uncoated endocytosis and trafficking from the Golgi apparatus.