Keep it together: knockdowns of dynactin subunits demonstrate varying levels of importance in dynactin structure and microtubule organization

Dynactin, a multisubunit protein complex, serves as a processivity factor and cargo adaptor for the microtubule motor cytoplasmic dynein. Together, these proteins permit mitotic progression, intracellular trafficking, and endomembrane organization. Dynactin also independently anchors microtubules at the centrosome during interphase. In this study, we use shRNAs to knock down expression of the p24, p27, p62, and Arp1 subunits of dynactin to determine those components’ roles in anchoring. Recent work has shown p62’s importance to dynactin integrity (Yeh et al., 2012), and we confirm that its loss disrupts microtubule organization. The peripheral p27 and binding partner p25 seem to contribute to membrane selectivity and have little effect on dynactin structure and anchoring. We find that an intact dynactin complex is necessary to maintain microtubule organization via the anchoring complex. While not directly bound to microtubules, these subunits provide crucial structural support to facilitate interactions among dynactin and other centrosomal anchoring components.