RESUMEN
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 beta-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.
Asunto(s)
Proteína de la Poliposis Adenomatosa del Colon/deficiencia , Apoptosis/fisiología , Mitosis/fisiología , Poliploidía , Proteína de la Poliposis Adenomatosa del Colon/genética , Animales , Apoptosis/efectos de los fármacos , Apoptosis/genética , Caspasa 3/metabolismo , Proteínas de Ciclo Celular , Línea Celular Tumoral , Cromatina/química , Cromatina/metabolismo , Ciclina B/metabolismo , Ciclina B1 , Inhibidor p21 de las Quinasas Dependientes de la Ciclina/metabolismo , Fibroblastos/efectos de los fármacos , Fibroblastos/metabolismo , Células HCT116 , Histonas/análisis , Humanos , Mucosa Intestinal/metabolismo , Intestinos/química , Intestinos/patología , Ratones , Ratones Transgénicos , Mitosis/efectos de los fármacos , Mitosis/genética , Modelos Biológicos , Nocodazol/farmacología , Paclitaxel/farmacología , Proteínas Quinasas/metabolismo , Proteínas Serina-Treonina Quinasas , ARN Interferente Pequeño/genética , Huso Acromático/metabolismo , Estaurosporina/farmacología , beta Catenina/análisis , beta Catenina/metabolismoRESUMEN
Oncogenic mutations in the K-ras gene occur in approximately 50% of human colorectal cancers. However, the precise role that K-ras oncogenes play in tumor formation is still unclear. To address this issue, we have conditionally expressed an oncogenic K-ras(V12) allele in the small intestine of adult mice either alone or in the context of Apc deficiency. We found that expression of K-ras(V12) does not affect normal intestinal homeostasis or the immediate phenotypes associated with Apc deficiency. Mechanistically we failed to find activation of the Raf/MEK/ERK pathway, which may be a consequence of the up-regulation of a number of negative feedback loops. However, K-ras(V12) expression accelerates intestinal tumorigenesis and confers invasive properties after Apc loss over the long term. In renal epithelium, expression of the oncogenic K-ras(V12) allele in the absence of Apc induces the rapid development of renal carcinoma. These tumors, unlike those of intestinal origin, display activation of the Raf/MEK/ERK and Akt signaling pathways. Taken together, these data indicate that normal intestinal and kidney epithelium are resistant to malignant transformation by an endogenous K-ras oncogene. However, activation of K-ras(V12) after Apc loss results in increased tumorigenesis with distinct kinetics. Whereas the effect of K-ras oncogenes in the intestine can been observed only after long latencies, they result in rapid carcinogenesis in the kidney epithelium. These data imply a window of opportunity for anti-K-ras therapies after tumor initiation in preventing tumor growth and invasion.