HURP controls spindle dynamics to promote proper interkinetochore tension and efficient kinetochore capture

Abstract

Through a functional genomic screen for mitotic regulators, we identified hepatoma up-regulated protein (HURP) as a protein that is required for chromosome congression and alignment. In HURP-depleted cells, the persistence of unaligned chromosomes and the reduction of tension across sister kinetochores on aligned chromosomes resulted in the activation of the spindle checkpoint. Although these defects transiently delayed mitotic progression, HeLa cells initiated anaphase without resolution of these deficiencies. This bypass of the checkpoint arrest provides a tumor-specific mechanism for chromosome missegregation and genomic instability. Mechanistically, HURP colocalized with the mitotic spindle in a concentration gradient increasing toward the chromosomes. HURP binds directly to microtubules in vitro and enhances their polymerization. In vivo, HURP stabilizes mitotic microtubules, promotes microtubule polymerization and bipolar spindle formation, and decreases the turnover rate of the mitotic spindle. Thus, HURP controls spindle stability and dynamics to achieve efficient kinetochore capture at prometaphase, timely chromosome congression to the metaphase plate, and proper interkinetochore tension for anaphase initiation.

RANBP1 localizes a subset of mitotic regulatory factors on spindle microtubules and regulates chromosome segregation in human cells

“…The association was lost upon MT depolymerization by NOC. This pattern is comparable to that of TPX2, a classical RAN-GTP-dependent MT-associated protein (MAP) (reviewed by Gruss and Vernos, 2004), and HURP, a recently characterized RAN-GTP-regulated factor that binds and stabilizes MTs (Wong and Fang, 2006;Koffa et al, 2006;Silljé et al, 2006). The MI is consistently lower in RANBP1(i) cultures compared with samples incubated with nonspecific siRNAs.…”

Centrobin regulates the assembly of functional mitotic spindles

“…The SAC prevents premature chromosome segregation through the inhibition of the anaphase-promoting complex/cyclosome, a ubiquitin ligase that initiates anaphase by mediating the destruction of Securin, allowing Cohesin cleavage by Separase; and cyclin B, the activating subunit of cyclin-dependent kinase 1 (Peters, 2002;Chung and Chen, 2003). However, a number of conditions can lead to SAC activation in metaphase cells including kinetochore malformation, defects in spindle dynamics and centrosome fragmentation as they prevent the formation of stable microtubule-kinetochore attachments (Lampson and Kapoor, 2005;Oshimori et al, 2006;Wong and Fang, 2006). The fidelity of the SAC is such that it can detect even a single unattached kinetochore (Rieder et al, 1994).…”

RanBP1 downregulation sensitizes cancer cells to taxol in a caspase-3-dependent manner

“…Roles of RanBP1 in control of MT function also emerge from RNA interference (RNAi) experiments: RanBP1-downregulated cells assemble mitotic spindles that are apparently normal but have altered properties, including resistance to MT depolymerization induced by chemical or physical agents, failure to associate with cyclin B1 and abnormal recruitment of the MT-stabilizing factor HURP (hepatoma up-regulated protein, itself viewed as a potential oncogene). HURP normally localizes to MT plus-ends and contributes to stabilize MT/kinetochore attachments (Koffa et al, 2006;Sillje et al, 2006;Wong and Fang, 2006), but it acquires a widespread distribution along the entire MT length on RanBP1 inactivation (Tedeschi et al, 2007). The resulting hyperstable MTs prolong or arrest prometaphase in video-recording experiments; many RanBP1-interfered cells actually undergo apoptosis after prolonged prometaphase delay, or progress further into mitosis and undergo inaccurate chromosome segregation (Li et al, 2007;Tedeschi et al, 2007).…”