PAK1 Signals to p41-Arc and N-WASP in Response to Insulin to Evoke Actin Remodeling and Glucose Uptake in Skeletal Muscle Cells

Presentation Number: LB SAT 80
Date of Presentation: April 1st, 2017

Ragadeepthi Tunduguru*1, Jing Zhang2, Jeffrey S Elmendorf3 and Debbie Thurmond1
1City of Hope, Duarte, CA, 2City of Hope BRI, Duarte, CA, 3Indiana University School of Medicine, Indianapolis, IN

Abstract

Defects in GLUT4 translocation are associated with peripheral insulin resistance, pre-clinical diabetes, and eventual progression to T2D. Recruitment of GLUT4 to the plasma membrane (PM) of skeletal muscle cells requires filamentous (F)-actin remodeling. Recent studies have shown that PAK1 signaling is required for insulin-induced actin remodeling and mediates GLUT4 vesicle translocation and glucose uptake into skeletal muscle cells, although the mode by which PAK1 regulates actin remodeling is unexplored. Additionally, in vitro data implicate the neural Wiskott- Aldrich syndrome protein (N-WASP), an actin binding protein, in insulin- dependent cortical F-actin rearrangement, however the mechanism of action involving N-WASP and its precise role in skeletal muscle function remains elusive. Here we show that inactivation of N-WASP by its specific inhibitor, Wiskostatin, fully abrogates the insulin-stimulated increase in PM GLUT4 recruitment in skeletal muscle cells. Furthermore, Wiskostatin fully ablated insulin-dependent glucose uptake into skeletal muscle cells. Toward interrogating the underlying mechanism, interactions between N- WASP and actin as well as other actin binding proteins, Cortactin and ARP2/3 complex, were assessed, given that the latter proteins are implicated in actin remodeling in clonal muscle cells. Indeed, a ~1.5 fold increased binding of Cortactin to N-WASP with insulin stimulation was detected using mouse skeletal muscle lysates. Moreover, interaction of N-WASP with both actin and p41-ARC (a regulatory subunit of the ARP2/3 complex) also increased upon insulin stimulation, and this interaction was abrogated upon inhibition of PAK activation by IPA3 (an inhibitor of PAK activation) in skeletal muscle cells. Interestingly, insulin-dependent p41-ARCT21 phosphorylation was significantly reduced in IPA3-treated skeletal muscle cells. In sum, these results suggest that PAK1 facilitates N-WASP, Cortactin and p41-ARC-mediated F-actin remodeling for insulin-stimulated GLUT4 vesicle translocation to the PM of skeletal muscle cells.

 

Nothing to Disclose: RT, JZ, JSE, DT