Could have a dual role in dynein targeting and in ACTR1A/Arp1 subunit of dynactin pointed-end capping. Could be involved in ACTR1A pointed-end binding and in additional roles in linking dynein and dynactin to the cortical cytoskeleton. Member of the pointed-end complex of the dynactin shoulder complex which contains DCTN4, DCTN5 and DCTN6 subunits and ACTR10 (By similarity). Binds directly to the ACTR1A subunit of dynactin. Interacts with ATP7B, but not ATP7A, in a copper-dependent manner. Interacts with ANK2; this interaction is required for localization at costameres (By similarity). Has a punctate cytoplasmic distribution as well as centrosomal distribution typical of dynactin (PubMed:10671518). Overexpression 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 (By similarity). In skeletal muscles, costamere localization requires the presence of ANK2 (By similarity). Belongs to the dynactin subunit 4 family.