Acentrosomal spindle organization renders cancer cells dependent on the kinesin HSET

Abstract

SummaryCentrosomes represent the major microtubule organizing centers (MTOCs) of animal somatic cells and orchestrate bipolar spindle assembly during mitotic cell division. In meiotic cells, the kinesin HSET compensates for the lack of centrosomes by focusing acentrosomal MTOCs into two spindle poles. By clustering multiple centrosomes into two spindle poles, HSET also mediates bipolar mitosis in cancer cells with supernumerary centrosomes. However, although dispensable in non-transformed human cells, the role of HSET in cancer cells with two centrosomes has remained elusive. In this study, we demonstrate that HSET is required for proper spindle assembly, stable pole-focusing and survival of cancer cells irrespective of normal or supernumerary centrosome number. Strikingly, we detected pronounced acentrosomal MTOC structures in untreated mitotic cancer cells. While in most cancer cells these acentrosomal MTOCs were rapidly incorporated into the assembling bipolar spindle, some cells eventually established bipolar spindles with acentrosomal poles and free centrosomes. These observations demonstrate that acentrosomal MTOCs were functional and that both centrosomal and acentrosomal mechanisms were required for bipolar spindle organization. Our study shows that HSET is critical for clustering acentrosomal and centrosomal MTOCs during spindle formation in human cancer cells with two bona fide centrosomes. Furthermore, we show that in checkpoint-defective cancer cells, acentrosomal spindle formation and HSET-dependence are partially mediated by a constitutive activation of the DNA damage response. In summary, we propose that acentrosomal spindle assembly mechanisms are hyperactive in cancer cells and promote HSET, a key driver of acentrosomal spindle organization, as an attractive target for cancer therapy.

Haspin kinase regulates microtubule-organizing center clustering and stability through Aurora kinase C in mouse oocytes

“…Mouse oocytes contain acentriolar centrosomes (MTOCs) that fragment and cluster to form meiosis I spindle poles. The mechanism by which oocytes use these MTOCs to build spindles is of great interest because of the high frequency of aneuploidy in female gametes (Hassold and Hunt, 2001), and the similarities of this clustering mechanism to that found in some cancers (Breuer et al, 2010;Kleylein-Sohn et al, 2012).…”

Causes and consequences of centrosome abnormalities in cancer

“…Depletion of HSET/KIFC1 in BT-549 cells caused not only centrosome declustering but also induced the formation of multipolar spindles with acentrosomal poles [147]. These observations demonstrate that HSET has a dual role in promoting bipolar spindle formation in cancer cells: promoting the clustering of extra centrosomes and the coalescence of acentrosomal poles that are aberrantly generated in BT-549 cells [147]. This study suggested that DNA damage signalling, which is commonly activated in cancer cells and is induced by many chemotherapeutic agents, contributes to the generation of acentrosomal spindle poles that need to be clustered to achieve a bipolar mitosis.…”

Using in Vivo Biotinylated Ubiquitin to Describe a Mitotic Exit Ubiquitome from Human Cells

“…E, immunoblotted extracts and NeutrAvidin pulldowns from cells synchronized as in D but released from prometaphase block for 15 min (metaphase, M*) or 30 min (C1 phase) were probed with anti-cyclin B1 antibody to reveal specific pulldown of ubiquitinated cyclin B1 from samples in which the SAC was inactivated. formation (52,53). During mitotic exit, KIFC1 has been shown to contribute to organization of the central spindle (54).…”