Mutational alterations of the PTEN gene located on chromosome 10q23.3 have been frequently observed in a variety of human malignancies, including glioblastoma, melanoma, prostate cancer and endometrial cancer. 1-7 PTEN mutations and allelic deletions at 10q23 appear to be late events in glioblastoma, melanoma and prostate cancer, while in thyroid and endometrial cancers, PTEN alterations are found at an early stage, such as endometrial hyperplasia and benign thyroid tumors. 4 -9 Frequent germline or somatic mutations of PTEN have also been found in patients with Cowden disease and Bannayan-Zonana syndrome, which are autosomal dominant disorders characterized by the formation of multiple benign tumors and increased risk of malignant breast and thyroid tumors. 10,11 The PTEN gene encodes a protein product which shares high homology in its N-terminal region with the cytoskeletal protein tensin and the secretary vesicle protein auxilin. 1,2 The PTEN protein also contains a structural motif for a dual-specificity protein phosphatase. 12 PTEN acts as a phospholipid phosphatase, dephosphorylating PIP 3 with specificity for the phosphate group at the D3 position of the inositol ring. 13 PIP 3 is a lipid second messenger produced by PI3-kinase and activates a variety of signaling effectors such as AKT kinase. The lipid phosphatase activity of PTEN is essential for its ability to inhibit tumorigenesis and growth inhibition. 14,15 In human tumor cells lacking wild-type PTEN or in PTEN-deficient mice, PIP 3 levels are increased, leading to enhanced phosphorylation and activation of the survivalpromoting factor AKT kinase, indicating that PTEN exerts its tumor-suppressor function by negatively regulating the antiapoptotic PI3-kinase/AKT signaling pathway. 16 In addition, in immortalized PTEN-deficient mouse embryonic fibroblasts, PTEN restored apoptosis induced by stimuli such as UV irradiation. 17 The role of PTEN as a tumor-suppressor has also been attributed to its ability to modulate cell-cycle progression and cell motility. Expression of wild-type PTEN in PTEN-null glioblastoma or renal cell carcinoma cells causes cell-cycle arrest in the G 1 phase, inhibits colony formation and suppresses tumorigenicity in nude mice. 18 Exogenous expression of PTEN in fibroblasts and a glioma cell line with mutant PTEN alleles also suppresses cell migration, integrin-mediated cell spreading and focal adhesion. 19

During tumour progression, cancer cells use diverse mechanisms to escape from apoptosis-inducing stimuli, which may include receptor internalization, inhibition of signal pathways, and regulation of specific sets of genes. Substantial numbers of colon cancer cells have been observed to express Fas/Fas ligand, but are resistant to Fas-mediated apoptosis, suggesting that colonic tumours might develop specific mechanisms to overcome Fas-mediated apoptosis. Recently, cellular FLICE-like inhibitory protein (cFLIP) has been identified as an endogenous inhibitor of Fas- or other receptor-mediated apoptosis and its altered high expression has a suspected association with tumour development or progression. In an effort to investigate the prevalence of cFLIP(L) alterations in colon carcinomas and their possible implications for the progression of colon cancers, cFLIP(L) expression was analysed in adenocarcinomas and adenomatous polyps of colon, with matched normal tissues, at RNA and protein levels, by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. cFLIP(L) transcripts were constitutively expressed in colon cancers and expression levels were significantly higher in carcinomas than in normal tissues (p<0.05). Overexpression of cFLIP(L) protein was found exclusively in carcinoma cells in all matched sets analysed and approximately three-fold induction was detected in cancer cells (p<0.05). The expression of cFLIP(L) protein was not significantly altered in adenomatous polyps compared with normal tissues. Taken together, these results strongly suggest that abnormal overexpression of cFLIP(L) is a frequent event in colon carcinomas and might contribute to in vivo tumour transformation.

Caveolin-1 (CAV1) acts as a growth suppressor in various human malignancies, but its expression is elevated in many advanced cancers, suggesting the oncogenic switch of its role during tumor progression. To understand the molecular basis for the growth-promoting function of CAV1, we characterized its expression status, differential roles for tumor growth, and effect on glucose metabolism in colorectal cancers. Abnormal elevation of CAV1 was detected in a substantial fraction of primary tumors and cell lines and tightly correlated with promoter CpG sites hypomethylation. Depletion of elevated CAV1 led to AMPK activation followed by a p53-dependent G 1 cell-cycle arrest and autophagy, suggesting that elevated CAV1 may contribute to ATP generation. Furthermore, CAV1 depletion downregulated glucose uptake, lactate accumulation, and intracellular ATP level, supporting that aerobic glycolysis is enhanced by CAV1. Consistently, CAV1 was shown to stimulate GLUT3 transcription via an HMGA1-binding site within the GLUT3 promoter. HMGA1 was found to interact with and activate the GLUT3 promoter and CAV1 increased the HMGA1 activity by enhancing its nuclear localization. Ectopic expression of HMGA1 increased glucose uptake, whereas its knockdown caused AMPK activation. In addition, GLUT3 expression was strongly induced by cotransfection of CAV1 and HMGA1, and its overexpression was observed predominantly in tumors harboring high levels of CAV1 and HMGA1. Together, these data show that elevated CAV1 upregulates glucose uptake and ATP production through HMGA1-mediated GLUT3 transcription, suggesting that CAV1 may render tumor cells growth advantages by enhancing aerobic glycolysis. Cancer Res; 72(16); 4097-109. Ó2012 AACR.

X-linked inhibitor of apoptosis (XIAP)-associated factor 1 (XAF1) is a tumor suppressor that is frequently inactivated in many human cancers. However, the molecular mechanism underlying its growthinhibitory function remains largely unknown. Here, we report that XAF1 forms a positive feedback loop with p53 and acts as a molecular switch in p53-mediated cell-fate decisions favoring apoptosis over cell-cycle arrest. XAF1 binds directly to the N-terminal prolinerich domain of p53 and thus interferes with E3 ubiquitin ligase MDM2 binding and ubiquitination of p53. XAF1 stimulates homeodomaininteracting protein kinase 2 (HIPK2)-mediated Ser-46 phosphorylation of p53 by blocking E3 ubiquitin ligase Siah2 interaction with and ubiquitination of HIPK2. XAF1 also steps up the termination of p53-mediated cell-cycle arrest by activating zinc finger protein 313 (ZNF313), a p21 WAF1 -targeting ubiquitin E3 ligase. XAF1 interacts with p53, Siah2, and ZNF313 through the zinc finger domains 5, 6, and 7, respectively, and truncated XAF1 isoforms preferentially expressed in cancer cells fail to form a feedback loop with p53. Together, this study uncovers a novel role for XAF1 in p53 stress response, adding a new layer of complexity to the mechanisms by which p53 determines cellfate decisions.

Introduction. Although combination therapy with herbal medicine and probiotics is gaining popularity for controlling diarrhea-dominant irritable bowel syndrome (D-IBS) symptoms, few studies have investigated its clinical effects. Materials and Methods. Fifty-three patients with D-IBS were randomly allocated into 1 of the following 4 groups: herbal medicine (Gwakhyangjeonggisan; GJS) plus probiotics (Duolac7S; DUO), GJS plus placebo DUO, placebo GJS plus DUO, and placebo GJS plus placebo DUO. The study period consisted of a 2-week run-in, 8 weeks of administration, and 2 weeks of follow-up. The primary outcomes were weekly adequate relief (AR) of overall IBS symptoms and the proportion of responders (PR) during the administration period. The secondary outcomes included individual IBS symptoms, stool assessment, and quality of life. Changes of intestinal microbiota and intestinal permeability were also analyzed. Results and Discussion. Weekly AR was not different among the 4 groups throughout the treatment period. However, the 3 treatment groups exhibited significant improvements in PR compared to the findings in the placebo group. In the intestinal microbiota assessment, herbal medicine and probiotics synergistically increased beneficial bacteria counts. Conclusion. Combination therapy with herbal medicine and probiotics appears to relieve overall IBS symptoms by synergistically increasing beneficial intestinal microbe counts.