Interaction of the p62 subunit of dynactin with Arp1 and the cortical actin cytoskeleton

Abstract

Targeting of the minus-end directed microtubule motor cytoplasmic dynein to a wide array of intracellular substrates appears to be mediated by an accessory factor known as dynactin [1-4]. Dynactin is a multi-subunit complex that contains a short actin-related protein 1 (Arp 1) filament with capZ at the barbed end and p62 at the pointed end [5]. The location of the p62 subunit and the proposed role for dynactin as a multifunctional targeting complex raise the possibility of a dual role for p62 in dynein targeting and in Arp1 pointed-end capping. In order to gain further insight into the role of p62 in dynactin function, we have cloned cDNAs that encode two full-length isoforms of the protein from rat brain. We found that p62 is homologous to the nuclear migration protein Ropy-2 from Neurospora [6]; both proteins contain a zinc-binding motif that resembles the LIM domain of several other cytoskeletal proteins [7]. Overexpression of p62 in cultured mammalian cells revealed colocalization with cortical actin, stress fibers, and focal adhesion sites, sites of potential interaction between microtubules and the cell cortex [8,9]. The p62 protein also colocalized with polymers of overexpressed wild-type or barbed-end-mutant Arp1, but not with a pointed-end mutant. Deletion of the LIM domain abolished targeting of p62 to focal-adhesion sites but did not interfere with binding of p62 to actin or Arp1. These data implicate p62 in Arp1 pointed-end binding and suggest additional roles in linking dynein and dynactin to the cortical cytoskeleton.

Interactions between the Evolutionarily Conserved, Actin-related Protein, Arp11, Actin, and Arp1

“…The pointed end complex protein, p62, may play a role in the association of Arp11 with the Arp1 minifilament. Like Arp11, p62 has been shown to bind to actin (Garces et al, 1999) and Arp1 (Karki et al, 2000) in vitro. If p62 and/or Arp11 is bound to actin, this would place actin at the pointed end of the Arp1 minifilament instead of in association with CapZ as we suggested previously (Schafer et al, 1994).…”

“…We assume actin coassembles with Arp1, but its exact location in the 37-nm minifilament is unknown. Either CapZ or p62 might interact with actin, because both proteins can bind actin filaments (Cooper and Pollard, 1985;Garces et al, 1999). Because p62 and CapZ are found at opposite ends of the Arp1 minifilament (Schafer et al, 1994), a rigorous assignment of actin's location within dynactin has not been possible.…”

Protein Kinase C-regulated Dynamitin-Macrophage-enriched Myristoylated Alanine-Rice C Kinase Substrate Interaction Is Involved in Macrophage Cell Spreading

“…Recent reports suggest that microtubules do not merely provide a structural reinforcement during cell spreading but also are involved in regulating focal adhesion (12,13). Recently, the p62 subunit of dynactin was shown to be involved in cell adhesion (66). Because dynamitin is an important regulator of the dynactin and microtubule function, it is feasible for dynamitin to be involved in cell spreading.…”

Alanine Scanning of Arp1 Delineates a Putative Binding Site for Jnm1/Dynamitin and Nip100/p150Glued

“…The role of the arp1-104 lethal charge cluster has been examined in the vertebrate dynactin complex (Garces et al, 1999). Residing at the pointed end of the Arp1 filament, this mutation specifically disrupted association with pointedend protein, p62, a subunit implicated in cargo binding (Eckley et al, 1999;Muresan et al, 2001;Salina et al, 2002).…”