Regulation of Dynamin Oligomerization in Cells: The Role of Dynamin–Actin Interactions and Its GTPase Activity

Abstract

Dynamin is a 96 kDa protein that has multiple oligomerization states that influence its GTPase activity. A number of different dynamin effectors, including lipids, actin filaments, and SH3-domain containing proteins, have been implicated in the regulation of dynamin oligomerization, though their roles in influencing dynamin oligomerization have been studied predominantly in vitro using recombinant proteins. Here, we identify higher order dynamin oligomers such as rings and helices in vitro and in live cells using fluorescence lifetime imaging microscopy (FLIM). FLIM detected GTP- and actin-dependent dynamin oligomerization at distinct cellular sites, including the cell membrane and transition zones where cortical actin transitions into stress fibers. Our study identifies a major role for direct dynamin-actin interactions and dynamin’s GTPase activity in the regulation of dynamin oligomerization in cells.

Drugs targeting dynamin can restore cytoskeleton and focal contact alterations of urinary podocytes derived from patients with nephrotic syndrome

“…Cleavage of dynamin by a cytoplasmic form of cathepsin L leads to reorganization of the podocyte actin cytoskeleton, podocyte failure and proteinuria. Dynamin mutants resistant to cathepsin L cleavage can restore podocyte function and resolve proteinuria (19,20). The double-knockout of dynamin 1 and dynamin 2 in mouse podocytes leads to podocyte effacement (21).…”

Podocytes and the actin cytoskeleton as a feasible therapeutic target

“…The molecular mechanism by which dynamin releases gelsolin from the barbed ends is at present unknown, but fluorescence lifetime imaging microscopy suggests that it requires GTP binding and a major conformational change within dynamin tetramers (40). The conformational change might be similar to the one suggested for dynamin assembly on the lipids (36,40).…”

“…Our recent study suggests that dynamin assembly presents an ideal pharmacological target as a proxy to target actin cytoskeleton dynamics (39). Another characteristic that distinguishes dynamin from canonical small GTPases is that dynamin directly binds actin filaments (10,40). Dynamin-actin interactions promote GTP-dependent dynamin oligomerization, which releases capping protein gelsolin from the barbed ends resulting in the potent actin polymerization from the fast growing barbed ends and focal adhesion maturation (25).…”

“…Dynamin-actin interactions promote GTP-dependent dynamin oligomerization, which releases capping protein gelsolin from the barbed ends resulting in the potent actin polymerization from the fast growing barbed ends and focal adhesion maturation (25). The molecular mechanism by which dynamin releases gelsolin from the barbed ends is at present unknown, but fluorescence lifetime imaging microscopy suggests that it requires GTP binding and a major conformational change within dynamin tetramers (40). The conformational change might be similar to the one suggested for dynamin assembly on the lipids (36,40).…”

“…Experiments using zebrafish further established the connection between dynamin-actin interactions, its oligomerization cycle, and function of podocytes by demonstrating that the expression of dynamin mutants impaired in either actin binding or assembly resulted in loss of high molecular weight protein from the circulation. In a complementary approach, administration of the small molecule Bis-T-23, which promotes actin-dependent dynamin oligomerization (40), and thus increases actin polymerization in injured podocytes, was sufficient to improve renal health in diverse models of both transient and chronic kidney injury. Specifically, Bis-T-23 restored the normal ultrastructure of foot processes, lowered proteinuria, lowered collagen IV deposits in the mesangial matrix, diminished mesangial matrix expansion, and extended lifespan.…”