Mad1 facilitates α5 integrin trafficking from the Golgi to promote abscission during cytokinesis

Mad1 is an essential component of the mitotic spindle assembly checkpoint. During interphase, Mad1 regulates the trafficking of α5 integrin from the Golgi to the plasma membrane. Here, we show that depletion of Mad1 or α5 integrin induces cytokinesis failure. Though the cytokinetic furrow ingresses with normal timing, it ultimately regresses, resulting in cytokinesis failure. We identify an ~300 amino acid internal fragment of Mad1 that is necessary and sufficient for the Golgi localization of Mad1. This fragment, which we term Mad1-Golgi, can rescue α5 integrin secretion and cytokinesis in Mad1-depleted cells. Expression of exogenous α5 integrin is sufficient to overcome the cytokinesis defect caused by Mad1 depletion. The contribution of both Mad1 and α5 integrin to cytokinesis is observed specifically under adherent growth conditions, and a pool of both proteins localizes to the midbody in adherent cells. These results demonstrate a previously uncharacterized role for Mad1 in cytokinesis by regulating α5 integrin secretion from the Golgi apparatus.