Increased GTP-binding to dynamin II does not stimulate receptor-mediated endocytosis

Increased association of dynamin II with myosin II in ras transformed NIH3T3 cells

Dynamin has been implicated in the formation of nascent vesicles through both endocytic and secretory pathways. However, dynamin has recently been implicated in altering the cell membrane shape during cell migration associated with cytoskeleton-related proteins. Myosin II has been implicated in maintaining cell morphology and in cellular movement. Therefore, reciprocal immunoprecipitation was carried out to identify the potential relationship between dynamin II and myosin II. The dynamin II expression level was higher when co-expressed with myosin II in Ras transformed NIH3T3 cells than in normal NIH3T3 cells. Confocal microscopy also confirmed the interaction between these two proteins. Interestingly, exposing the NIH3T3 cells to platelet-derived growth factor altered the interaction and localization of these two proteins. The platelet-derived growth factor treatment induced lamellipodia and cell migration, and dynamin II interacted with myosin II. Grb2, a 24 kDa adaptor protein and an essential element of the Ras signaling pathway, was found to be associated with dynamin II and myosin II gene expression in the Ras transformed NIH3T3 cells. These results suggest that dynamin II acts as an intermediate messenger in the Ras signal transduction pathway leading to membrane ruffling and cell migration.

Phospholipase C-gamma1 is a guanine nucleotide exchange factor for dynamin-1 and enhances dynamin-1-dependent epidermal growth factor receptor endocytosis

Phospholipase C-gamma1 (PLC-gamma1), which interacts with a variety of signaling molecules through its two Src homology (SH) 2 domains and a single SH3 domain has been implicated in the regulation of many cellular functions. We demonstrate that PLC-gamma1 acts as a guanine nucleotide exchange factor (GEF) of dynamin-1, a 100 kDa GTPase protein, which is involved in clathrin-mediated endocytosis of epidermal growth factor (EGF) receptor. Overexpression of PLC-gamma1 increases endocytosis of the EGF receptor by increasing guanine nucleotide exchange activity of dynamin-1. The GEF activity of PLC-gamma1 is mediated by the direct interaction of its SH3 domain with dynamin-1. EGF-dependent activation of ERK and serum response element (SRE) are both up-regulated in PC12 cells stably overexpressing PLC-gamma1, but knockdown of PLC-gamma1 by siRNA significantly reduces ERK activation. These results establish a new role for PLC-gamma1 in the regulation of endocytosis and suggest that endocytosis of activated EGF receptors may mediate PLC-gamma1-dependent proliferation.

The dynamin A ring complex: molecular organization and nucleotide-dependent conformational changes

Here we show that Dictyostelium discoideum dynamin A is a fast GTPase, binds to negatively charged lipids, and self-assembles into rings and helices in a nucleotide-dependent manner, similar to human dynamin-1. Chemical modification of two cysteine residues, positioned in the middle domain and GTPase effector domain (GED), leads to altered assembly properties and the stabilization of a highly regular ring complex. Single particle analysis of this dynamin A* ring complex led to a three-dimensional map, which shows that the nucleotide-free complex consists of two layers with 11-fold symmetry. Our results reveal the molecular organization of the complex and indicate the importance of the middle domain and GED for the assembly of dynamin family proteins. Nucleotide-dependent changes observed with the unmodified and modified protein support a mechanochemical action of dynamin, in which tightening and stretching of a helix contribute to membrane fission.