The Kru¨ppel-like zinc-finger protein GLI1 functions as a downstream transcription factor of Hedgehog signaling and plays a pivotal role in the cellular proliferation of many types of tumors, including pancreatic ductal adenocarcinoma (PDA). PDA develops from dysplastic lesions called pancreatic intraepithelial neoplasia (PanIN) through a multistep carcinogenesis process that changes its cellular characteristics, including a mucin expression profile. Increased expression of a gel-forming mucin, MUC5AC, was previously revealed as a major biomarker for the poor prognosis of PDA patients, but the molecular mechanisms responsible for its expression and correlation with poor prognosis are not fully understood. Here we show that MUC5AC is a direct transcriptional target of GLI1 in PDA cells. Overexpression of GLI1 enhanced MUC5AC expression, and a double knockdown of GLI1 and GLI2 suppressed endogenous MUC5AC expression in PDA cells. Luciferase reporter assays revealed that GLI1 and GLI2 can activate the MUC5AC promoter through its conserved CACCC-box-like cis-regulatory elements. We also found that GLI1-upregulated MUC5AC was expressed in the intercellular junction between cultured PDA cells and interfered with the membrane localization of E-cadherin, leading to decreased E-cadherin-dependent cell-cell adhesion and promoting the migration and invasion of PDA cells. Consistently, GLI1 induced the nuclear accumulation and target gene expression of b-catenin in a MUC5AC-dependent manner. Finally, immunohistochemical analysis revealed that GLI1 expression statistically correlated with MUC5AC expression and also with altered subcellular localization of E-cadherin and b-catenin in PanIN lesions and PDA. This evidence revealed a new aspect of GLI1 function in modulating E-cadherin/ b-catenin-regulated cancer cell properties through the expression of a gel-forming mucin.

The CD274 (PD-L1)/PDCD1 (PD-1) pathway is crucial for the modulation of immune responses and self-tolerance. Aberrantly expressed CD274 allows tumor cells to evade host immune system and is considered to be a mechanism of adaptive immune resistance. Inhibition of the CD274/PDCD1 immune checkpoint offers a promising new therapeutic strategy. Although CD274-expressing tumor cells have been identified in different types of tumors including colorectal cancer, clinicopathologic profile of these CD274-positive tumors has not been extensively studied. In this study, 454 primary colorectal carcinomas were analyzed histologically and immunohistochemically for CD274, mismatch repair (MMR) proteins, intestinal differentiation marker (CDX2), and stem cell markers (ALCAM, ALDH1A1, and SALL4). CD274-positive colorectal carcinomas (54/454 (12%)) usually (83%) involved the right or transverse colon with poorly differentiated and solid/medullary histology. On the basis of multivariate logistic regression analysis, CD274 positivity was significantly associated with poorly differentiated histotype (OR: 3.32; 95% CI: 1.46-7.51; P=0.004), MMR deficiency (OR: 10.0; 95% CI: 4.66-21.5; P<0.001), and 'stem-like' immunophenotype defined by the loss or weak expression of CDX2 and ALCAM-positivity (OR: 5.51; 95% CI: 1.66-18.3; P=0.005). Mutation analysis of 66 arbitrary selected colorectal carcinomas revealed that CD274-positive tumors usually (88%) carried the BRAF V600E mutation. Thus, colorectal carcinomas defined by CD274 positivity displayed features associated with tumors arising via the serrated neoplasia pathway. Moreover, colorectal carcinomas characterized by lack of CDX2 and prominent expression of ALCAM frequently (71%) showed CD274 positivity. This might suggest association of CD274 expression with 'stem-like' phenotype. Further evaluation of a larger cohort or experimental analyses would be needed to confirm this notion.

As a physically binding protein of GLI1 transcription factor, Suppressor-of-Fused (SUFU) has been placed in the center of negative regulation of Hedgehog (Hh) signaling. SUFU tethers GLI1 in cytoplasm, and in some circumstances, it moves into the nucleus in association with GLI1, leading to the suppression of GLI1 target gene expression by recruiting a corepressor complex. The activated transcriptional function of GLI1 is important for cellular proliferation in a variety of human cancers. However, it has not been revealed how GLI1 is derepressed from SUFU-mediated suppression. Here, we show SCL/TAL1 interrupting locus (SIL) product, a cytoplasmic protein overexpressed in pancreatic ductal adenocarcinoma (PDA), is responsible for the derepression of GLI1. We found SIL associated with the carboxyl terminus of SUFU, one of two distinct GLI1-binding domains, and this association was responsible for cytoplasmic tethering of SUFU. Overexpressed SIL attenuated SUFU-mediated cytoplasmic tethering and target gene suppression of GLI1. Knockdown of SIL in PDA cells conversely induced the nuclear accumulation of SUFU in association with GLI1 and the transcriptional suppression of GLI1 target genes. Importantly, we also showed that oncogenic K-RAS, and not Sonic hedgehog, enhanced the SIL association with the amino-terminus of SUFU, the other GLI1-binding domain that led to further increase of nuclear translocation of GLI1. These results uncover the role of SIL in derepressing GLI1 from the negative control of SUFU, which is a crucial step for activating Hh signaling in cancer cells. [Cancer Res 2008;68(19):7723-9]

Mesothelin (MSLN) is a glycophosphatidylinositol (GPI)-linked cell surface protein highly expressed in several types of malignant tumors sometimes in association with increased tumor aggressiveness and poor clinical outcome. In the present study, 1562 tumors were immunohistochemically analyzed for mesothelin expression using two different types of mouse monoclonal antibodies (5B2 and MN-1) to determine the clinical usefulness of mesothelin immunohistochemistry as well as to pinpoint potential targets for future anti-mesothelin therapy. Also, characterization of selected mesothelin-positive tumors was performed by immunohistochemistry and oncogene sequencing. Among the tumors analyzed, the highest frequencies of mesothelin-positivity were detected in ovarian serous carcinoma (90% in 5B2 and 94% in MN-1). Both antibodies showed frequent positivity in pancreatic adenocarcinoma (71% using 5B2 and 87% using MN-1) and malignant pleural mesothelioma (75% using 5B2 and 78% using MN-1). In malignant mesothelioma, overall survival was significantly longer in the cohort of patients with diffuse membranous expression of mesothelin (P < 0.001). Both antibodies showed positive staining in thymic carcinoma (77% in 5B2 and 59% in MN-1), however, no expression was detected in thymoma. No correlation was detected between mesothelin expression and mismatch repair system deficient phenotype or gene mutation (BRAF and RAS) status in gastrointestinal adenocarcinomas. Mesothelin immunohistochemistry may assist the differential diagnosis of thymoma vs. thymic carcinoma as well as prognostication of mesothelioma patients. Our results demonstrate that patients with solid tumors expressing mesothelin could be targeted by anti-mesothelin therapies.