Recently it was reported that Crm is linked

Recently, it was reported that Crm1 is linked to spindle pole body (SPB) by Spc72 in CRT0044876 yeast [9]. Spc72 and Spc110 are two specific receptors of γ-tubulin complex (Tub4), which target Tub4 to SPB and mediate the nucleation of microtubules from SPB [20]. It was found that disrupting the interaction between Spc72 and Crm1 by NES mutation of Spc72 or by Crm1 mutants could affect the mitotic spindle morphology and microtubule nucleation [9]. More interestingly, although the homology of Spc72 in vertebrate has not been found yet, pericentrin is known to be the ortholog of Spc110 and plays a role in anchoring γ-tubulin to centrosomes [21]. Our data also showed that Crm1 knockdown disrupted the spindle pole localization of pericentrin and γ-tubulin, and caused the mitotic abnormalities, including chromosomes misalignment and multipolar spindles. It suggests that the mechanism of Crm1 to regulate the structure and function of centrosomes might be conserved from yeast to vertebrate animals.
Acknowledgments
R cell carcinoma is the sixth most common cancer in the United States and one of the few cancers whose incidence is increasing. Five-year survival of patients with metastatic RCC is dismal., For the third of patients who present at the metastatic stage several Food and Drug Administration approved drugs are available, among them the multikinase inhibitors, of which some (eg sorafenib) also inhibit p21 and mammalian target of rapamycin inhibitors. Since even with these new drugs progression-free survival is only 1 to 2 years, it is imperative that novel therapeutic targets for metastatic RCC be identified and validated. CRM1 is the receptor for the canonical nuclear export sequences and it mediates the nuclear export of nuclear export sequences containing proteins, including the TSPs p53 and p21., CRM1 over expression, leading to increased nuclear export of TSPs, is a poor prognostic factor for many cancers, including ovarian, liver and pancreatic cancer., In addition, multiple studies showed that CRM1 inhibition induces apoptosis and inhibits tumor growth in several cancer cell lines., However, despite abundant knowledge that subcellular TSP localization is important for RCC behavior, to our knowledge there are no published studies of CRM1 inhibition in RCC.
Introduction Chromosome region maintenance 1/exportin1/Xpo1 (CRM1) belongs to the β-karyopherin protein family of importins and exportins that transport macromolecular cargos between the nucleus and the cytosol (Cook and Conti, 2010). CRM1 is regulated by the small GTPase Ran, whose GTP-bound form is abundant in the nucleus and scarce in the cytosol. CRM1 associates cooperatively with its cargos and with RanGTP in the nucleus, forming a ternary complex that traverses the nuclear pore complex (NPC) and dissociates in the cytosol with the aid of Ran-binding factors (RanBP1, RanBP2, and RanGAP) that promote cargo release and GTP hydrolysis. Whereas most exportins recognize one or only a few structurally related cargos, CRM1 exports a wide diversity of cargos, including many tumor suppressors, oncoproteins, and viral proteins (Güttler and Görlich, 2011, Xu et al., 2012b), making CRM1 an attractive target for fighting malignancy and disease (Etchin et al., 2012, Lapalombella et al., 2012, Turner et al., 2012). CRM1 recognizes its cargos through their leucine-rich nuclear export signal (NES), a short motif characterized by four or five hydrophobic residues (Güttler et al., 2010, Xu et al., 2012a). Like all exportins, CRM1 has intrinsically weak cargo-binding affinity that is strongly enhanced by RanGTP. This is crucial for transport directionality, ensuring that CRM1 binds cargos in the nucleus and releases them in the cytosol. Atomic structures of mammalian and fungal CRM1, alone and in complex with different binding partners, have revealed that CRM1 undergoes multiple conformational changes as it shuttles between the nucleus, where cooperative assembly of the CRM1/Ran/cargo complex occurs, and the cytosol, where the complex disassembles (Dong et al., 2009b, Güttler et al., 2010, Koyama and Matsuura, 2010, Monecke et al., 2009, Monecke et al., 2013, Saito and Matsuura, 2012). Human CRM1 consists of 1,071 residues organized into 20 (or 21 depending on numbering convention; Dong et al., 2009b, Monecke et al., 2009) tandem HEAT repeats, each forming a hairpin of helices denoted A and B. The repeats define a ring-shaped solenoid, whose outer and inner surfaces comprise the A and B helices, respectively. Ran binds inside the ring, engaging the B helices of N- and C-terminal repeats and an acidic loop within HEAT-repeat 9. The NES binds to CRM1’s outer surface, occupying a groove formed by the A helices of repeats 11 and 12 (Dong et al., 2009b, Güttler et al., 2010, Monecke et al., 2009). The helical NES motifs of Snurportin1 (Spn1) and protein kinase A inhibitor (PKI) and the more extended NES motif of HIV-1 Rev dock into a common set of five hydrophobic pockets within this groove (Güttler et al., 2010). The disassembly factor RanBP1 promotes cargo release from the CRM1/Ran/NES complex by inducing the HEAT-9 loop to switch from a conformation interacting with Ran to a conformation interacting with the B helices behind the NES-binding groove, causing the latter to constrict and extrude the bound NES (Koyama and Matsuura, 2010). In the absence of Ran, the HEAT-9 loop plays an auto-inhibitory role by maintaining the NES-binding groove in a constricted conformation incompatible with NES binding (Fox et al., 2011, Monecke et al., 2013, Saito and Matsuura, 2012).