Myosin I, the Arp2/3 Complex, and Actin Dynamics: Fusion proteins containing the SH3 domains of Dictyostelium myosin IB (myoB) and IC (myoC) bind a 116kDa protein (p116), plus nine other proteins identified by microsequencing as the seven-member Arp2/3 complex, CapZ alpha and CapZ beta. Immunoprecipitations performed using wild type and mutant cell extracts indicate that myoB and myoC are present in a complex with p116, Arp2/3, and CapZ in vivo, that their SH3 domains are required for this interaction, and, together with other experiments, that p116 acts as a scaffold, binding myosin I, CapZ, and the Arp2/3 complex at independent sites. Cloning of p116 reveals a leucine-rich- repeat domain, a WASP-like WH2/acidic domain, and proline-rich sequences which we show contain the SH3 domain binding site, and indicates that p116 is a Dictyostelium homolog of Acan 125. p116 colocalizes extensively with Arp3, actin, coronin, myoB and myoC in dynamic actin-rich cellular extensions, especially the leading edge of migrating cells and dorsal, cup-like, macropinocytic extensions (crowns). p116 knockout cells exhibit a profound defect in the formation of these macropinocytic structures, and a concomitant reduction in the rate of fluid phase endocytosis (~ 50% of WT). MyoB/myoC double mutants also exhibit a striking defect in crown formation (but with interesting differences) and partially mislocalize Arp3. These results identify a complex linking the major actin filament nucleator and barbed-end capper to a ubiquitous barbed-end-directed motor, indicate that this complex is physiologically important, and suggest that previously reported myosin I mutant phenotypes are due at least in part to defects in the function of Arp2/3 and CapZ.Myosin V and Melanosome Dynamics: Previous studies have shown that myosin V localizes to melanosomes in mouse melanocytes, and that it cooperates with microtubule motors to drive the peripheral accumulation of melanosomes characteristic of mammalian melanocytes. The domain of myosin V that is responsible for the interaction with the melanosome has been mapped and is now being used to search for the myosin V receptor on the melanosome surface. - Arp2/3 complex, myosin I, actin dynamics, myosin V, melanosomes, melanocytes, mouse, Dictyostelium

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Intramural Research (Z01)
Project #
1Z01HL000514-16
Application #
6290376
Study Section
Special Emphasis Panel (LCB)
Project Start
Project End
Budget Start
Budget End
Support Year
16
Fiscal Year
1999
Total Cost
Indirect Cost
Name
National Heart, Lung, and Blood Institute
Department
Type
DUNS #
City
State
Country
United States
Zip Code
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Wu, Xufeng; Xiang, Xin; Hammer 3rd, John A (2006) Motor proteins at the microtubule plus-end. Trends Cell Biol 16:135-43
Uruno, Takehito; Remmert, Kirsten; Hammer 3rd, John A (2006) CARMIL is a potent capping protein antagonist: identification of a conserved CARMIL domain that inhibits the activity of capping protein and uncaps capped actin filaments. J Biol Chem 281:10635-50
Thirumurugan, Kavitha; Sakamoto, Takeshi; Hammer 3rd, John A et al. (2006) The cargo-binding domain regulates structure and activity of myosin 5. Nature 442:212-5
Wu, Xufeng S; Tsan, Grace L; Hammer 3rd, John A (2005) Melanophilin and myosin Va track the microtubule plus end on EB1. J Cell Biol 171:201-7

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