Loss of APC induces polyploidy as a result of a combination of defects in mitosis and apoptosis

Abstract

Mutations in the adenomatous polyposis coli (APC) tumor suppressor gene initiate a majority of colorectal cancers. Acquisition of chromosomal instability is an early event in these tumors. We provide evidence that the loss of APC leads to a partial loss of interkinetochore tension at metaphase and alters mitotic progression. Furthermore, we show that inhibition of APC in U2OS cells compromises the mitotic spindle checkpoint. This is accompanied by a decrease in the association of the checkpoint proteins Bub1 and BubR1 with kinetochores. Additionally, APC depletion reduced apoptosis. As expected from this combination of defects, tetraploidy and polyploidy are consequences of APC inhibition in vitro and in vivo. The removal of APC produced the same defects in HCT116 cells that have constitutively active β-catenin. These data show that the loss of APC immediately induces chromosomal instability as a result of a combination of mitotic and apoptotic defects. We suggest that these defects amplify each other to increase the incidence of tetra- and polyploidy in early stages of tumorigenesis.

Rapamycin inhibits oncogenic intestinal ion channels and neoplasia in APCMin/+ mice

“…Erg channels are activated by Akt (Zhang et al, 2003) and confer greater malignancy to patients with leukemia (Pillozzi et al, 2007). Moreover, mutations in the APC gene alter cell cycling (Dikovskaya et al, 2007), and as Eag family channels are cell cycle regulated (Wonderlin and Strobl, 1996), it is likely that these changes affect their activity. In this study, Eag family channels, Erg1 and Elk1, were upregulated in the colon of APC Min/ þ mice, but rapamycin treatment reduced the level of upregulation toward normalization.…”

Cyclin A/cdk2 Regulates Adenomatous Polyposis Coli-dependent Mitotic Spindle Anchoring

“…indicate that depletion of APC reduces checkpoint fidelity (32). The basis for this disagreement is not clear, although it may reflect cell type difference or the relative depletion of APC achieved in each case (3).…”

“…Equal amounts of protein (300 -500 g per sample) were immunoprecipitated with either anti-cyclin A and 30 l of protein A-Sepharose or GST-APC bound to glutathione-Sepharose overnight at 4°C. The precipitates were washed three times with NETN buffer and once with KB buffer (20 mM Tris, pH 7.5, 1 mM dithiothreitol) before incubating in 30 l of RC buffer (20 mM Tris, pH 7.5, 15 mM MgCl 2 , 0.5 mg/ml histone H1, 5 Ci [␥- 32 P]ATP per sample) for 15 min at 30°C. The labeled proteins were resolved on 10% SDS-PAGE and quantitated by phosphorimaging.…”

Germline mutation contribution to chromosomal instability

“…In support of the contribution of APC to microtubule stability, APCdepleted cells were found to be more sensitive than wildtype cells to treatment of the microtubule-depolymerizing drug vinorelbine (Klotz et al 2012), suggesting that disrupted microtubule dynamics is a feature of cells with impaired APC function and may be a potential therapeutic target for APC-deficient cancers. Apart from affecting kinetochore-microtubule interactions, loss of functional APC may also compromise the SAC through inefficient localization of BUB1 and BUBR1 to kinetochores as well as inappropriately activating the Wnt signaling pathway via stabilization of β-catenin, leading to increased susceptibility to CIN , Dikovskaya et al 2007, Caldwell & Kaplan 2009, Pino & Chung 2010. While these experimental findings as well as observations of elevated CIN in low-grade dysplastic polyps of FAP patients (Cardoso et al 2006) and in murine intestinal adenomas with germline mutations in APC (Alberici et al 2007 provide support for constitutional depletion of APC in predisposition to CIN (Aoki & Taketo 2007, Pino & Chung 2010, there have been contradicting findings that argued otherwise (Haigis et al 2002, Sieber et al 2002, Aoki & Taketo 2007.…”