Lissencephaly-1 is a context-dependent regulator of the human dynein complex

Abstract

The cytoplasmic dynein-1 (dynein) motor plays a central role in microtubule organisation and cargo transport. These functions are spatially regulated by association of dynein and its accessory complex dynactin with dynamic microtubule plus ends. Here, we elucidate in vitro the roles of dynactin, end-binding protein-1 (EB1) and Lissencephaly-1 (LIS1) in the interaction of end tracking and minus end-directed human dynein complexes with these sites. LIS1 promotes dynactin-dependent tracking of dynein on both growing and shrinking plus ends. LIS1 also increases the frequency and velocity of processive dynein movements that are activated by complex formation with dynactin and a cargo adaptor. This stimulatory effect of LIS1 contrasts sharply with its documented ability to inhibit the activity of isolated dyneins. Collectively, our findings shed light on how mammalian dynein complexes associate with dynamic microtubules and help clarify how LIS1 promotes the plus-end localisation and cargo transport functions of dynein in vivo.DOI: http://dx.doi.org/10.7554/eLife.21768.001

Combinatorial regulation of the balance between dynein microtubule end accumulation and initiation of directed motility

“…Dynactin has a triple role: (i) it mediates EB‐dependent plus‐end tracking of dynein, in the absence of other regulators (Fig 1), in agreement with recent work (Baumbach et al , 2017) (ii) it activates BicD2‐dependent dynein processivity (Fig 2), as shown before on static microtubules (McKenney et al , 2014; Schlager et al , 2014); and (iii) it biases dynein motility initiation from microtubule plus‐end regions (Figs 3 and 4). EB‐dependent end tracking of dynein/dynactin contributes additionally to biasing motility initiation towards microtubule plus ends, likely by increasing the local concentration of dynein/dynactin there.…”

“…The microtubule recruitment factor Lis1 adds an additional layer of regulation (Fig 5). It promotes efficient EB‐dependent plus‐end tracking of dynein/dynactin, especially in the presence of BicD2, and in cooperation with BicD2, Lis1 also promotes initiation of processive motility, in agreement with recent work (Baumbach et al , 2017). …”

“…This preference for growing microtubule ends and GMPCPP microtubules was, however, not observed in a recent in vitro study, possibly due to the higher ionic strength buffer used in that study (Baumbach et al , 2017). The nucleotide sensitivity of p150 under our experimental conditions is strikingly similar to that of the unrelated microtubule binding protein TPX2 that was also observed to strongly bind to GMPCPP microtubules and to growing microtubule ends independently of EB proteins (Roostalu et al , 2015).…”

“…Addition of 200 nM Alexa647‐labelled SNAP‐tagged BicD2‐N (Alexa647‐BicD2‐N) to a reconstitution assay with dynamic microtubules, dynein, dynactin and EB1 leads now to the appearance of processive and lattice‐bound GFP‐dyneins in addition to plus‐end accumulated dynein (Fig 2A). This is one of the first observations of processive human dynein motility on dynamic microtubules using purified proteins (Baumbach et al , 2017). …”

“…Reducing Lis1 levels in fungi and mammalian cells inhibits dynein‐dependent transport of several organelles (Pandey & Smith, 2011; Egan et al , 2012; Dix et al , 2013; Moughamian et al , 2013; Klinman & Holzbaur, 2015) and BicD2‐N carrying vesicles (Splinter et al , 2012) in agreement with the simultaneous requirement of Lis1 and BicD2 for transport initiation as observed in our minimal system. A positive effect of Lis1 on DDB initiations was also noted in one (Baumbach et al , 2017), but not in another (Gutierrez et al , 2017) recent in vitro study. Also for cells, some opposing findings were reported: a reduction in Lis1 levels in Drosophila cells was shown to enhance dynein‐dependent transport of mitochondria (Vagnoni et al , 2016), suggesting that Lis1 can also have an inhibitory effect on transport initiation, potentially when it is in excess over cargo adaptors.…”