Regulators of the cytoplasmic dynein motor

Abstract

Eukaryotic cells use cytoskeletal motor proteins to transport many different intracellular cargos. Numerous kinesins and myosins have evolved to cope with the various transport needs that have arisen during eukaryotic evolution. Surprisingly, a single cytoplasmic dynein (a minus end-directed microtubule motor) carries out similarly diverse transport activities as the many different types of kinesin. How is dynein coupled to its wide range of cargos and how is it spatially and temporally regulated? The answer could lie in the several multifunctional adaptors, including dynactin, lissencephaly 1, nuclear distribution protein E (NUDE) and NUDE-like, Bicaudal D, Rod-ZW10-Zwilch and Spindly, that regulate dynein function and localization.

Figure 1. Multiple factors cooperate to target dynein to microtubule plus ends and to its cargos

a | Several factors contribute to dynein localization to the microtubule plus ends. The localization of CAP-Gly domain-containing linker protein 170 (CLIP170) and dynactin to the microtubule plus end usually depends on end binding 1 (EB1), although all three factors can interact directly with tubulin. Lissencephaly 1 (LIS1) is probably recruited to the plus end by interacting with CLIP170. LIS1–nuclear distribution protein E (NUDE) or LIS1–NUDE-like (NUDEL) and dynactin then target dynein to the plus end. The microtubule-binding domains of dynein might also contribute to its association with the microtubule plus ends. Solid arrows indicate biochemically confirmed physical interactions; the dotted arrow indicates an interaction shown by yeast two-hybrid assay. b | Following recruitment to microtubule plus ends by the interactions shown in part a, dynein can probe the cytoplasm for cargo such as an organelle or the cell cortex, although in some cases dynein might be recruited to cargo directly from the cytosol. Once dynein is loaded with cargo, LIS1–NudE or LIS1–NudEL and dynactin promote its release from the microtubule plus end and the initiation of motility through an as yet unknown mechanism. Cargo binding is achieved by the interaction of dynein with specific receptors, directly or through dynactin and the cargo linker Bicaudal d, and by the interaction of dynactin with spectrin, a filamentous protein that coats the cytoplasmic face of the Golgi and other cell membranes. These interactions might be required sequentially or in combination. dynein transports organelles and other cargos along microtubules, or can slide microtubules relative to its position when it is anchored at the cell cortex (lower right panel). It is not known whether LIS1-NudE and LIS1–NudEL contribute to this step.

Figure 2. Adaptor proteins couple dynein to multiple functions at the mitotic kinetochore

a | Interactions with several adaptor proteins (dynactin, the Rod–ZW10–Zwilch (RZZ) complex, Spindly, lissencephaly 1 (LIS1), nuclear distribution protein E (NUDE) and NudE-like (NUDEL)) link dynein to the kinetochore. RZZ, NudE and NudEL interact directly with kinetochore proteins and recruit the other adaptors to the kinetochore^–,. Some of these interactions could occur simultaneously, but others seem specific to a distinct mitotic stage. In particular, the RZZ-interacting phosphorylated epitope on the dynein complex is only present before chromosome alignment. The hierarchy of these interactions also varies between systems: dynactin is required for nearly all dynein recruitment, whereas LIS1 is only sometimes required^,,,,. Spindly is required for dynactin recruitment in human cells and Caenorhabditis elegans embryos, but not Drosophila melanogaster S2 cells^,,,. After chromosome alignment, connections between the kinetochore and the dynein machinery are broken (crossed arrows), and dynein begins transport of the spindle assembly checkpoint (SAC) proteins towards the spindle poles. Solid arrows represent known physical interactions, and dashed arrows represent interactions inferred from localization dependencies. b | dynein localizes to unattached kinetochores by interacting with LIS1–NudE or LIS1–NudEL and dynactin, and possibly through a direct interaction with the RZZ complex. dynein captures astral microtubules and transports chromosomes towards the spindle poles, promoting ‘end-on’ microtubule attachment and chromosome alignment. dynactin, LIS1–NudE, LIS1–NudEL and RZZ–Spindly are important for this process because they link dynein to the kinetochore and perhaps also regulate the motor activity of dynein. After chromosomes form bi-oriented microtubule attachments, dynein transports SAC proteins towards the spindle poles, which helps to silence the checkpoint and allow anaphase progression.