Mutations in PIK3C2A cause syndromic short stature, skeletal abnormalities, and cataracts associated with ciliary dysfunction

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Mitotic Spindle Assembly and Genomic Stability in Breast Cancer Require PI3K-C2α Scaffolding Function

Proper organization of the mitotic spindle is key to genetic stability, but molecular components of inter-microtubule bridges that crosslink kinetochore fibers (K-fibers) are still largely unknown. Here we identify a kinase-independent function of class II phosphoinositide 3-OH kinase \uce\ub1 (PI3K-C2\uce\ub1) acting as limiting scaffold protein organizing clathrin and TACC3 complex crosslinking K-fibers. Downregulation of PI3K-C2\uce\ub1 causes spindle alterations, delayed anaphase onset, and aneuploidy, indicating that PI3K-C2\uce\ub1 expression is required for genomic stability. Reduced abundance of PI3K-C2\uce\ub1 in breast cancer models initially impairs tumor growth but later leads to the convergent evolution of fast-growing clones with mitotic checkpoint defects. As a consequence of altered spindle, loss of PI3K-C2\uce\ub1 increases sensitivity to taxane-based therapy in pre-clinical models and in neoadjuvant settings. Gulluni et al. reveal a kinase-independent scaffolding function of PI3K-C2\uce\ub1 that affects mitotic spindle formation. Reduced levels of PI3K-C2\uce\ub1 reduce tumor growth initially but provide a growth advantage later in mouse models of breast cancer. Loss of PI3K-C2\uce\ub1 also increases sensitivity of tumors to taxanes

Downregulation of class II phosphoinositide 3-kinase PI3K-C2β delays cell division and potentiates the effect of docetaxel on cancer cell growth.

BACKGROUND: Alteration of signalling pathways regulating cell cycle progression is a common feature of cancer cells. Several drugs targeting distinct phases of the cell cycle have been developed but the inability of many of them to discriminate between normal and cancer cells has strongly limited their clinical potential because of their reduced efficacy at the concentrations used to limit adverse side effects. Mechanisms of resistance have also been described, further affecting their efficacy. Identification of novel targets that can potentiate the effect of these drugs or overcome drug resistance can provide a useful strategy to exploit the anti-cancer properties of these agents to their fullest. METHODS: The class II PI3K isoform PI3K-C2β was downregulated in prostate cancer PC3 cells and cervical cancer HeLa cells using selective siRNAs and the effect on cell growth was determined in the absence or presence of the microtubule-stabilizing agent/anti-cancer drug docetaxel. Mitosis progression was monitored by time-lapse microscopy. Clonogenic assays were performed to determine the ability of PC3 and HeLa cells to form colonies upon PI3K-C2β downregulation in the absence or presence of docetaxel. Cell multi-nucleation was assessed by immunofluorescence. Tumour growth in vivo was assessed using a xenograft model of PC3 cells upon PI3K-C2β downregulation and in combination with docetaxel. RESULTS: Downregulation of PI3K-C2β delays mitosis progression in PC3 and HeLa cells, resulting in reduced ability to form colonies in clonogenic assays in vitro. Compared to control cells, PC3 cells lacking PI3K-C2β form smaller and more compact colonies in vitro and they form tumours more slowly in vivo in the first weeks after cells implant. Stable and transient PI3K-C2β downregulation potentiates the effect of low concentrations of docetaxel on cancer cell growth. Combination of PI3K-C2β downregulation and docetaxel almost completely prevents colonies formation in clonogenic assays in vitro and strongly inhibits tumour growth in vivo. CONCLUSIONS: These data reveal a novel role for the class II PI3K PI3K-C2β during mitosis progression. Furthermore, data indicate that blockade of PI3K-C2β might represent a novel strategy to potentiate the effect of docetaxel on cancer cell growth.This work was supported by Prostate Cancer UK through a Project grant (grant PG13–029 to TM and MF). OC was supported by Prostate Cancer UK (grant PG13–029). IM was supported by MRC a MRC Doctoral Training Award to Barts and The London School of Medicine and Dentistry. FG is supported by Fondazione Italiana Ricerca Cancro (FIRC 19421). EH acknowledges funding from Associazione Italiana Ricerca Cancro (AIRC 21875)