βIII Spectrin Binds to the Arp1 Subunit of Dynactin

Abstract

Cytoplasmic dynein is an intracellular motor responsible for endoplasmic reticulum-to-Golgi vesicle trafficking and retrograde axonal transport. The accessory protein dynactin has been proposed to mediate the association of dynein with vesicular cargo. Dynactin contains a 37-nm filament made up of the actin-related protein, Arp1, which may interact with a vesicle-associated spectrin network. Here, we demonstrate that Arp1 binds directly to the Golgi-associated ␤III spectrin isoform. We identify two Arp1-binding sites in ␤III spectrin, one of which overlaps with the actin-binding site conserved among spectrins. Although conventional actin binds weakly to ␤III spectrin, Arp1 binds robustly in the presence of excess F-actin. Dynein, dynactin, and ␤III spectrin co-purify on vesicles isolated from rat brain, and ␤III spectrin co-immunoprecipitates with dynactin from rat brain cytosol. In interphase cells, ␤III spectrin and dynactin both localize to cytoplasmic vesicles, co-localizing most significantly in the perinuclear region of the cell. In dividing cells, ␤III spectrin and dynactin co-localize to the developing cleavage furrow and mitotic spindle, a novel localization for ␤III spectrin. We hypothesize that the interaction between ␤III spectrin and Arp1 recruits dynein and dynactin to intracellular membranes and provides a direct link between the microtubule motor complex and its membrane-bounded cargo.The microtubule-based motor cytoplasmic dynein is involved in a wide range of cellular processes, including retrograde transport in neurons, trafficking of vesicles from the endoplasmic reticulum to the Golgi, mitotic spindle assembly, and potentially cytokinesis (reviewed in Ref. 1). These processes require the targeting of dynein to many different cellular cargoes. Whereas dynein clearly provides a motile force in all of these processes, the mechanisms linking dynein to these various cargoes have yet to be identified (reviewed in Ref. 2).Dynactin is a multi-subunit complex that binds both to microtubules (3) and to cytoplasmic dynein (4, 5). Disruption of the dynein-dynactin interaction blocks dynein-mediated transport both in vitro and in vivo (6 -9). The specific role of the interaction between dynein and dynactin is unknown. One possibility is that dynactin increases the processive nature of the movement of dynein along cellular microtubules (3, 10). A second but not mutually exclusive hypothesis is that dynactin links dynein to its cellular cargo (11).Although a dynactin-independent association between a dynein light chain and the rhodopsin receptor has been detected in rod cell vesicles (12), other studies suggest that dynactin is required to mediate the interaction of dynein with vesicular cargo. Antibodies that block the dynein-dynactin interaction deplete dynein from vesicles and inhibit microtubule-based vesicular transport (6, 7). Furthermore, disruption of the dynein-dynactin interaction by dynamitin overexpression inhibits dynein-mediated vesicle trafficking in cells (9). The nature of the interaction ...

Evidence for a Functional Interaction between the ClC-2 Chloride Channel and the Retrograde Motor Dynein Complex

“…On the other hand, it is well known that dynactin interacts with and activates cytoplasmic dynein (33). Further, it has been shown that dynactin may recruit dynein to cargo in membrane vesicles directly (34) or indirectly via cytoskeletal proteins such as spectrin (35)(36)(37). Hence, in our future work, we will test the prediction that dynactin and spectrin may mediate the interaction between ClC-2 and dynein.…”

The retromer component SNX6 interacts with dynactin p150Glued and mediates endosome-to-TGN transport

“…For example, the Golgi protein Bicaudal-D binds to both dynein and the p50/dynamitin subunit of dynactin to regulate COP1-independent Golgi-ER transport [6][7][8]. Another Golgi-associated protein, βIII spectrin, binds to the Arp1 subunit of dynactin and is believed to link the motor to membranous cargo [9]. The huntingtin protein facilitates vesicular transport of brain-derived neurotrophic factor via the interaction between huntingtin-associated protein-1 and p150 Glued [10,11].…”

Arl3 and LC8 regulate dissociation of dynactin from dynein

“…Importantly, dynactin has been found to be essential for nearly every cellular function of cytoplasmic dynein, such as cargo loading, dynein localization and maintaining processivity 5,8 . For example, Arp1 filament of dynactin binds to bIII spectrin, a filamentous protein that is found on the cytosolic surface of the Golgi and other cellular membranes 9 . Dynactin p150 Glued is also an important component for connection of a dynactin complex with a dynein motor.…”