No abstract

Increasing epidemiological and experimental evidence implicates non-steroidal anti-in¯ammatory drugs (NSAIDs) as anti-tumorigenic agents. The precise mechanisms whereby NSAIDs exert their anti-neoplastic eects remain poorly understood. Studies from hereditary and sporadic colorectal cancer (CRC) patients suggest that NSAIDs may interfere with initiating steps of carcinogenesis, i.e. disturbances within the b-catenin signaling pathway. We therefore investigated b-catenin/ TCF signaling in response to aspirin or indomethacin, respectively, in four CRC cell lines (SW948, SW480, HCT116, LoVo). Both, aspirin and indomethacin inhibited transcription of a b-catenin/TCF-responsive reporter gene in a dose dependent manner. In addition, the b-catenin/TCF transcriptional target cyclin D1 was downregulated by both drugs. Endogenous b-catenin levels remained unaected by either drug. Moreover, indirect immuno¯uorescence studies revealed no signi®-cant changes of subcellular b-catenin localization in either cell line after NSAID treatment. Likewise, binding of the b-catenin/TCF complex to its speci®c DNAbinding sites was not altered, as demonstrated by electrophoretic mobility shift assay (EMSA) of nuclear extracts derived from NSAID treated cells. These results strongly suggest that aspirin and indomethacin attenuate the transcription of b-catenin/TCF-responsive genes, by modulating TCF activity without disrupting b-catenin/ TCF complex formation. Oncogene (2001) 20, 645 ± 653.

Functional studies on colorectal cancer cells indicated a protective role of the interferon-inducible dsDNA sensor Absent in Melanoma 2 (AIM2) in cancer progression. Given that a high mutation rate and lack of AIM2 expression was previously detected in a subset of colorectal cancers, we here investigated the association of AIM2 expression in tumor cells and patient prognosis (5-year follow-up). A tissue microarray analysis of 476 matched tissue pairs (colorectal tumor and adjacent normal colon epithelium) was performed by two independent observers. Samples from 62 patients were excluded because of missing follow-up information or due to neo-adjuvant therapy before tissue sampling. Out of the remaining 414 tissue pairs, 279 (67.4%) displayed reduced AIM2 expression in cancer cells when compared to epithelial cells of their normal counterpart. Thirty-eight patients (9.18%) had completely lost AIM2 expression in tumor cells. After adjustment for sex, age, cancer stage, tumor site, tumor grade and chemotherapy, complete lack of AIM2 expression was associated with an up to 3-fold increase in overall mortality (HR 5 2.40; 95% CI 5 1.44-3.99) and disease specific mortality (HR 5 3.14; 95% CI 5 1.75-5.65) in comparison to AIM2-positive tumor samples. Our results demonstrate that lack of AIM2 expression is closely associated with poor outcome in colorectal cancer. The data thus strongly substantiate a protective role of AIM2 against progression of colorectal tumors. Further studies are required to assess whether lack of AIM2 expression may be used as a biomarker for the identification of colorectal cancer patients with poor prognosis.Colorectal cancer is a heterogeneous disease with regard to molecular pathogenesis and clinical course, which makes it difficult to select patients who will benefit from adjuvant therapies. Today, the management of colorectal cancer is mainly based on the clinicopathological stage of the tumor (using UICC TNM classification), which accounts for local tumor infiltration depth, lymph node and distant organ metastasis. 1 Following resection of the primary tumor, adjuvant cytotoxic chemotherapy is offered as the standard treatment for patients with Stage III cancers, i.e., tumors with metastases to the regional lymph nodes but no distant metastases. In these patients, adjuvant chemotherapy reduces the risk of disease recurrence or metachronous metastasis. 2,3 However, there has been debate over the survival benefit of this adjuvant treatment, in particular for patients with Stage II cancers, i.e., infiltrating tumors without detectable metastases. 4,5 Given that the disease-free 5-year survival rate of Stage III patients ranges between 58.9% and 66. 4%, 6 and that up to 20% of Stage I and II patients develop metachronous extranodal metastasis within 4 years after apparently curative resection, 7 early identification of high risk groups that might

Mismatch repair (MMR) deficiency is a major mechanism of colorectal tumorigenesis that is observed in 10-15% of sporadic colorectal cancers and those associated with the hereditary nonpolyposis colorectal cancer (HNPCC) syndrome. MMR deficiency leads to the accumulation of mutations mainly at short repetitive sequences termed microsatellites, constituting the high level microsatellite instability (MSI-H) phenotype. In recent years, several genes have been described that harbor microsatellites in their coding region (coding microsatellites, cMS) and are frequently affected by mutations in MMR-deficient cancers. However, evidence for a functional role of most of the known cMS-containing genes is missing, and further analyses are needed for a better understanding of MSI tumorigenesis. Here, we examined in detail alterations of the absent in melanoma 2 (AIM2) gene that shows a high frequency of cMS frameshift mutations in MSI-H colorectal, gastric, and endometrial tumors. AIM2 belongs to the HIN-200 family of interferon (IFN)-inducible proteins, its role in colon carcinogenesis, however, is unknown. Sequencing of the entire coding region of AIM2 revealed a high frequency of frameshift and missense mutations in primary MSI-H colon cancers (9/20) and cell lines (9/15). Biallelic AIM2 alterations were detected in 8 MSI-H colon tumors and cell lines. In addition, AIM2 promoter hypermethylation conferred insensitivity to IFN-gamma-induced AIM2 expression of three MSI-H colon cancer cell lines. These results demonstrate that inactivation of AIM2 by genetic and epigenetic mechanisms is frequent in MMR-deficient colorectal cancers, thus suggesting that AIM2 is a mutational target relevant for the progression of MSI-H colorectal cancers.