Domain requirements for an endocytosis-independent, isoform-specific function of dynamin-2.

Endocytosis is inhibited by overexpression of either dynamin-1 or dynamin-2 mutants because both isoforms form heterotetramers with endogenous dynamin-2 and interfere with its function. By contrast, other phenotypes, which are specifically triggered by overexpression of dynamin-2, but not dynamin-1 are likely to reflect endocytosis-independent, dynamin-2-specific functions and/or interactions. Using Dyn2/Dyn1 chimeras, we explored the structural requirements for a readily quantifiable, isoform-specific function of dynamin-2, the activation of caspase-3 to trigger apoptosis. Strikingly, swapping the highly homologous GTPase domain of dynamin-2 into dynamin-1 was sufficient to confer caspase-3 activation. Moreover, assembly-defective mutations in GED, dynamin's GAP/assembly domain, that inhibit endocytosis enhance caspase-3 activation. Thus, this dynamin-2-specific function is mechanistically distinct from and independent of its role in endocytosis. These findings have important implications for interpreting dynamin-2 dependent phenotypes in overexpression studies.