Publications (3)108.84 Total impact
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Article: CKI[agr] ablation highlights a critical role for p53 in invasiveness control
Nature 02/2011; 470(7334):409-413. · 36.28 Impact Factor -
Article: CKIα ablation highlights a critical role for p53 in invasiveness control.
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ABSTRACT: The mature gut renews continuously and rapidly throughout adult life, often in a damage-inflicting micro-environment. The major driving force for self-renewal of the intestinal epithelium is the Wnt-mediated signalling pathway, and Wnt signalling is frequently hyperactivated in colorectal cancer. Here we show that casein kinase Iα (CKIα), a component of the β-catenin-destruction complex, is a critical regulator of the Wnt signalling pathway. Inducing the ablation of Csnk1a1 (the gene encoding CKIα) in the gut triggers massive Wnt activation, surprisingly without causing tumorigenesis. CKIα-deficient epithelium shows many of the features of human colorectal tumours in addition to Wnt activation, in particular the induction of the DNA damage response and cellular senescence, both of which are thought to provide a barrier against malignant transformation. The epithelial DNA damage response in mice is accompanied by substantial activation of p53, suggesting that the p53 pathway may counteract the pro-tumorigenic effects of Wnt hyperactivation. Notably, the transition from benign adenomas to invasive colorectal cancer in humans is typically linked to p53 inactivation, underscoring the importance of p53 as a safeguard against malignant progression; however, the mechanism of p53-mediated tumour suppression is unknown. We show that the maintenance of intestinal homeostasis in CKIα-deficient gut requires p53-mediated growth control, because the combined ablation of Csnk1a1 and either p53 or its target gene p21 (also known as Waf1, Cip1, Sdi1 and Cdkn1a) triggered high-grade dysplasia with extensive proliferation. Unexpectedly, these ablations also induced non-proliferating cells to invade the villous lamina propria rapidly, producing invasive carcinomas throughout the small bowel. Furthermore, in p53-deficient gut, loss of heterozygosity of the gene encoding CKIα caused a highly invasive carcinoma, indicating that CKIα functions as a tumour suppressor when p53 is inactivated. We identified a set of genes (the p53-suppressed invasiveness signature, PSIS) that is activated by the loss of both p53 and CKIα and which probably accounts for the brisk induction of invasiveness. PSIS transcription and tumour invasion were suppressed by p21, independently of cell cycle control. Restraining tissue invasion through suppressing PSIS expression is thus a novel tumour-suppressor function of wild-type p53.Nature 02/2011; 470(7334):409-13. · 36.28 Impact Factor -
Article: CKIa ablation highlights a critical role for p53 in invasiveness control
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ABSTRACT: The mature gut renews continuously and rapidly throughout adult life, often in a damage-inflicting micro-environment. The major driving force for self-renewal of the intestinal epithelium is the Wnt-mediated signalling pathway, and Wnt signalling is frequently hyperactivated in colorectal cancer 1 . Here we show that casein kinase Ia (CKIa), a component of the b-catenin-destruction complex 1 , is a critical regulator of the Wnt signalling pathway. Inducing the abla-tion of Csnk1a1 (the gene encoding CKIa) in the gut triggers massive Wnt activation, surprisingly without causing tumorigenesis. CKIa-deficient epithelium shows many of the features of human colorectal tumours in addition to Wnt activation, in particular the induction of the DNA damage response and cellular senescence, both of which are thought to provide a barrier against malignant transformation 2 . The epithelial DNA damage response in mice is accompanied by substan-tial activation of p53, suggesting that the p53 pathway may counter-act the pro-tumorigenic effects of Wnt hyperactivation. Notably, the transition from benign adenomas to invasive colorectal cancer in humans is typically linked to p53 inactivation, underscoring the importance of p53 as a safeguard against malignant progression 3 ; however, the mechanism of p53-mediated tumour suppression is unknown. We show that the maintenance of intestinal homeostasis in CKIa-deficient gut requires p53-mediated growth control, because the combined ablation of Csnk1a1 and either p53 or its target gene p21 (also known as Waf1, Cip1, Sdi1 and Cdkn1a) triggered high-grade dysplasia with extensive proliferation. Unexpectedly, these ablations also induced non-proliferating cells to invade the villous lamina propria rapidly, producing invasive carcinomas throughout the small bowel. Furthermore, in p53-deficient gut, loss of hetero-zygosity of the gene encoding CKIa caused a highly invasive car-cinoma, indicating that CKIa functions as a tumour suppressor when p53 is inactivated. We identified a set of genes (the p53-suppressed invasiveness signature, PSIS) that is activated by the loss of both p53 and CKIa and which probably accounts for the brisk induction of invasiveness. PSIS transcription and tumour invasion were sup-pressed by p21, independently of cell cycle control. Restraining tissue invasion through suppressing PSIS expression is thus a novel tumour-suppressor function of wild-type p53. To investigate the physiological roles of CKIa, we generated mice in which Csnk1a1 was either deleted from the germline or loxP flanked (floxed) and therefore able to be conditionally deleted (Supplemen-tary Fig. 1a). Whereas mice that were heterozygous for Csnk1a1 (Csnk1a1 1/2) seemed to be normal, homozygous deficiency was embryonic lethal before embryonic day 6.5 (Supplementary Fig. 1b and Supplementary Table 1), suggesting a fundamental role for CKIa in embryogenesis. To study the role of CKIa in gut physiology, we crossed mice in which Csnk1a1 was floxed with mice expressing Vil1–Cre–ER T2 , generating animals in which injection with tamoxifen causes deletion of the gene encoding CKIa exclusively in the intestinal epithelium (hereafter termed Csnk1a1 Dgut mice). Within 5 days of treatment with tamoxifen, CKIa expression was largely abolished throughout the epithelia of the small bowel (Fig. 1a, b and Supplementary Fig. 2a) and colon (data not shown), and was absent for at least 2 weeks, indicating that intestinal progenitor cells had been targeted by the recombinase Cre. CKIa loss was accompanied by a mild increase in CKId expression (Supplemen-tary Fig. 2b), while the priming phosphorylation of b-catenin on the serine residue at position 45 (S45) was abolished, eliminating the rest of the phosphorylation cascade (T41, S37 and S33) (Fig. 1b). Con-sequently, b-catenin was stabilized in the cytoplasm and nucleus, including in differentiated cells of the villus (Fig. 1a, b and Supplemen-tary Fig. 2d). Using RKO cells (a human colorectal cancer cell line), we confirmed this non-redundant function of the a-isoform of CKI in vitro (Supplementary Fig. 2c). These findings indicate that CKIa is indispensable for initiating the b-catenin phosphorylation–degradation cascade in the gut epithelium. As expected, b-catenin accumulation in the gut of Csnk1a1 Dgut mice was accompanied by robust activation of many Wnt target genes, including Myc, Axin2, Sox9, Cd44 and the genes encoding cyclin D1 and cyclin D2 (http:,rnusse/pathways/targets. html) (Fig. 1c, d). Particularly striking was the distinct nuclear expres-sion of cyclin D1, which spread into all villi throughout the small intestine. By contrast, in wild-type small bowel, cyclin D1 was restricted to the crypts. Likewise, CD44 and Myc were overexpressed in Csnk1a1 Dgut (Fig. 1d). In other mouse models of Wnt hyperactivation, ectopic Paneth cells are common 4 , and these are clearly observed in small-bowel villi of Csnk1a1 Dgut mice (Supplementary Fig. 2e). Thus, knockout of the gene encoding CKIa induced b-catenin stabilization and a massive Wnt response, comparable to other mouse models of Wnt activation and to colorectal cancers. Surprisingly, despite the robust activation of mitogenic Wnt target genes, gut homeostasis was preserved, and tumorigenesis was not observed. This is in stark contrast to Wnt activation in the mouse gut after deletion of the adenomatosis polyposis coli (Apc) gene, which resulted in immediate dysplastic transformation of the entire bowel and rapid death 4 . Instead, we found only mild atypia and minimal small-bowel crypt elongation, owing to an approximately twofold increase in the proliferating cell population (Supplementary Fig. 2e and data not shown). We therefore postulated that Csnk1a1 ablation elicits a simultaneous reaction that restrains the hyperproliferation and tumorigenesis that is expected on Wnt hyperactivation. Phenotypic changes in Csnk1a1 Dgut mice might resemble the onco-gene-induced senescence 5 associated with DNA-replication stress, persistent DNA damage 6 and apoptosis 7 . Accordingly, p19 ARF , a hall-mark of oncogene-induced senescence 8 , was found to be upregulatedNature 01/2011; · 36.28 Impact Factor
Top co-authors
Institutions
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2011
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Hebrew University of Jerusalem
- Lautenberg Center for Immunology and Cancer Research
Jerusalem, Jerusalem District, Israel
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