CLIP-170 is a plus-end tracking protein which may act as an anticatastrophe factor. It has been proposed to mediate the association of dynein/dynactin to microtubule (MT) plus ends, and it also binds to kinetochores in a dynein/dynactin-dependent fashion, both via its C-terminal domain. This domain contains two zinc finger motifs (proximal and distal), which are hypothesized to mediate protein-protein interactions. LIS1, a protein implicated in brain development, acts in several processes mediated by the dynein/dynactin pathway by interacting with dynein and other proteins. Here we demonstrate colocalization and direct interaction between CLIP-170 and LIS1. In mammalian cells, LIS1 recruitment to kinetochores is dynein/dynactin dependent, and recruitment there of CLIP-170 is dependent on its site of binding to LIS1, located in the distal zinc finger motif. Overexpression of CLIP-170 results in a zinc finger-dependent localization of a phospho-LIS1 isoform and dynactin to MT bundles, raising the possibility that CLIP-170 and LIS1 regulate dynein/dynactin binding to MTs. This work suggests that LIS1 is a regulated adapter between CLIP-170 and cytoplasmic dynein at sites involved in cargo-MT loading, and/or in the control of MT dynamics.

The mitotic spindle is often positioned in a characteristic location during development, for example to enable the proper segregation of developmental determinants [1,2]. When epithelial cells divide, the mitotic spindle is often positioned parallel to the plane of the epithelium, so that both daughter cells contribute to the epithelium [3]. The mechanisms by which mitotic spindles are positioned have not been characterized in great detail, but evidence is accumulating that in some systems the dynein-dynactin microtubule motor complex plays a role [4-6]. Dynein has yet not been localized to cortical sites where it could bind to microtubules and exert a force that might orient the mitotic spindle, however [7,8]. Here, we report that in mitotic polarized epithelial cells, the dynein-dynactin complex accumulates, from prometaphase onwards, along astral microtubules and at cortical spots, into which many of the astral microtubules dock. The spots are assembled at the lateral plasma membrane, in the region below the tight junctions. Their formation is inhibited by cytochalasin D, and under these conditions the spindles do not orient properly. This novel localization of the dynein-dynactin complex is consistent with a role for the complex in the positioning of the mitotic spindle. We also show that, during prophase, the motor complex colocalizes with the nuclear envelope, consistent with it having a role in separating the centrosomes that are associated with the nuclear envelope.