Impaired Glycosylation of Gastric Mucins Drives Gastric Tumorigenesis and Serves as a Novel Therapeutic Target.

BACKGROUND & AIMS: Gastric cancer is often accompanied by a loss of mucin 6 (MUC6), but its pathogenic role in gastric carcinogenesis remains unclear. METHODS: Muc6 knockout (Muc6-/-) mice and Muc6-dsRED mice were newly generated. Tff1Cre, Golph3-/-, R26-Golgi-mCherry, Hes1flox/flox, Cosmcflox/flox, and A4gnt-/- mice were also used. Histology, DNA and RNA, proteins, and sugar chains were analyzed by whole-exon DNA sequence, RNA sequence, immunohistochemistry, lectin-binding assays, and liquid chromatography-mass spectrometry analysis. Gastric organoids and cell lines were used for in vitro assays and xenograft experiments. RESULTS: Deletion of Muc6 in mice spontaneously causes pan-gastritis and invasive gastric cancers. Muc6-deficient tumor growth was dependent on mitogen-activated protein kinase activation, mediated by Golgi stress-induced up-regulation of Golgi phosphoprotein 3. Glycomic profiling revealed aberrant expression of mannose-rich N-linked glycans in gastric tumors, detected with banana lectin in association with lack of MUC6 expression. We identified a precursor of clusterin as a binding partner of mannose glycans. Mitogen-activated protein kinase activation, Golgi stress responses, and aberrant mannose expression are found in separate Cosmc- and A4gnt-deficient mouse models that lack normal O-glycosylation. Banana lectin-drug conjugates proved an effective treatment for mannose-rich murine and human gastric cancer. CONCLUSIONS: We propose that Golgi stress responses and aberrant glycans are important drivers of and promising new therapeutic targets for gastric cancer.

Staphylococcal superantigen-like protein 3 triggers murine mast cell adhesion by binding to CD43 and augments mast cell activation.

Staphylococcus aureus is a noteworthy pathogen in allergic diseases, as four staphylococcal exotoxins activate mast cells, a significant contributor to inflammation, in an IgE-independent manner. Although the adhesion of mast cells is an essential process for their immune responses, only a small number of exotoxins have been reported to affect the process. Here, we demonstrated that staphylococcal superantigen-like (SSL) 3, previously identified as a toll-like receptor 2 agonist, induced the adhesion of murine bone marrow-derived mast cells to culture substratum. SSL3-induced adhesion was mediated by fibronectin in an Arg-Gly-Asp (RGD) sequence-dependent manner, suggesting the integrins were involved in the process. Additionally, SSL3 was found to bind to an anti-adhesive surface protein CD43. SSL3 induced the adhesion of HEK293 cells expressing exogenous CD43, suggesting that CD43 is the target molecule for adhesion induced by SSL3. Evaluation of SSL3-derived mutants showed that the C-terminal region (253-326), specifically T285 and H307, are necessary to induce adhesion. SSL3 augmented the IL-13 production of mast cells in response to immunocomplex and SSL12. These findings reveal a novel function of SSL3, triggering cell adhesion and enhancing mast cell activation. This study would clarify the correlation between S. aureus and allergic diseases such as atopic dermatitis.

Sirt3 Regulates Proliferation and Progesterone Production in Leydig Cells via Suppression of Reactive Oxygen Species.

Sirt3 is a mitochondrial protein deacetylase functioning in energy metabolism, regulation of intracellular reactive oxygen species (ROS) levels, and aging. Although Sirt3 loss has negative effects on fertility of oocytes during in vitro fertilization and on progesterone production in granulosa cells, Sirt3's function in Leydig cells remains unclear. Therefore, we investigated Sirt3 activity in Leydig cells, focusing on androgen production. To do so, we performed immunohistochemistry to confirm Sirt3 localization in gonads and observed strong Sirt3 immunostaining in Leydig cells of human testes and of Sirt3+/+ and Sirt3+/- mouse testes, while Sirt3-/- mouse testis tissue was negative. In human ovary, hilus cells were strongly Sirt3-positive, theca cells showed weak positivity, and granulosa cells showed very weak or almost no immunostaining. Next, we used the murine Leydig tumor cell line MA-10 as a model. We overexpressed Sirt3 but observed no changes in proliferation, expression of Star, Cyp11a1 (p450scc gene), and Hsd3b, or progesterone production in MA-10 cells. Sirt3 knockdown significantly reduced proliferation, suppressed expressions of steroidogenic enzymes and of transcription factors Ad4bp (Sf-1 gene) and Gata4, and decreased progesterone production. Sirt3 knockdown in MA-10 cells also increased intracellular ROS levels based on CM-H2DCFDA fluorescence dye analysis and increased the proportion of both early and late apoptotic (necrotic) cells based on Annexin V/7AAD assays. These results indicate that Sirt3 has a potential function in androgen production in Leydig cells by regulating intracellular ROS levels.

Identification of Terminal ßGlcNAc on Brachyspira Species in Human Intestinal Spirochetosis.

Human intestinal spirochetosis (HIS) is a colorectal bacterial infection caused by the Brachyspira species. Griffonia simplicifolia-II (GS-II) is a lectin specific to terminal α/ßGlcNAc residues. Here, we investigated terminal ßGlcNAc residues in the context of HIS infection using GS-II-horseradish peroxidase staining and HIK1083 immunostaining specific to terminal αGlcNAc residues. Fourteen of 15 HIS cases were GS-II-positive on the bacterial body. No cases showed HIK1083 positivity. The percentage of bacterial bodies staining positively for GS-II based on comparison with anti-Treponema immunostaining was ≤30% in seven cases, 30-70% in two, and >70% in six. Of 15 HIS cases analyzed, none were comorbid with tubular adenomas, and three were comorbid with sessile serrated lesions (SSLs). To determine the species of spirochete infected, the B. aalborgi-specific or B. pilosicoli-specific NADPH oxidase genes were amplified by PCR. After direct sequencing of the PCR products, all nine cases in which PCR products were observed were found to be infected with B. aalborgi alone. These results indicate that the HIS bacterial body, especially of B. aalborgi, is characterized by terminal ßGlcNAc and also indicate that terminal ßGlcNAc on the HIS bacterial body is associated with HIS preference for SSLs.

Decreased expression of TFF2 and decreased αGlcNAc glycosylation are malignant biomarkers of pyloric gland adenoma of the duodenum.

Pyloric gland adenoma (PGA) is a duodenal neoplasm expressing MUC6 and is often associated with high-grade dysplasia and adenocarcinoma. MUC6 secreted from the pyloric gland cells carries unique O-glycans exhibiting terminal α1,4-linked N-acetylglucosamine residues (αGlcNAc). The small peptide trefoil factor 2 (TFF2) is also secreted from pyloric gland cells and binds to αGlcNAc. We recently demonstrated that αGlcNAc serves as a tumor suppressor for gastric neoplasm including PGA, but the significance of TFF2 expression remains unknown. We examined 20 lesions representing low- and high-grade PGA in 22 cases by immunohistochemistry for αGlcNAc, TFF2, MUC6, MUC5AC, MUC2 and p53. αGlcNAc, TFF2 and MUC6 were co-expressed on the cell surface and a dot-like pattern in the cytosol in low-grade PGA lesions. High-grade PGA also expressed MUC6, but reduced αGlcNAc and TFF2 expression. The ratios of αGlcNAc or TFF2 to MUC6 score in high-grade PGA were significantly lower than low-grade PGA (P < 0.001). Co-expression of αGlcNAc-glycosylated MUC6 and TFF2 in PGA suggests the existence of αGlcNAc/TFF2 form complex in PGA cells, a finding consistent with our observations in non-neoplastic Brunner's gland cells. The decreased αGlcNAc and TFF2 expression are associated with high grade atypical cells, indicative of the malignant potential of PGA.

α1,4-Linked N-acetylglucosamine suppresses gastric cancer development by inhibiting Mucin-1-mediated signaling.

Gastric cancer is the second leading cause of cancer deaths worldwide, and more understanding of its molecular basis is urgently needed. Gastric gland mucin secreted from pyloric gland cells, mucous neck cells, and cardiac gland cells of the gastric mucosa harbors unique O-glycans carrying terminal α1,4-linked N-acetylglucosamine (αGlcNAc) residues. We previously reported that αGlcNAc loss correlated positively with poor outcomes for patients with differentiated-type gastric cancer. However, the molecular mechanisms underlying these outcomes remained poorly understood. Here, we examined the effects of upregulated αGlcNAc expression on malignant phenotypes of the differentiated-type gastric cancer cell lines, AGS and MKN7. Upregulation of αGlcNAc following ectopic expression of its biosynthetic enzyme attenuated cell proliferation, motility, and invasiveness of AGS and MKN7 cells in vitro. Moreover, AGS cell tumorigenicity was significantly suppressed by αGlcNAc overexpression in a xenograft model. To define the molecular mechanisms underlying these phenotypes, we investigated αGlcNAc binding proteins in AGS cells and identified Mucin-1 (MUC1) and podocalyxin. Both proteins were colocalized with αGlcNAc on human gastric cancer cells. We also found that αGlcNAc was bound to MUC1 in murine normal gastric mucosa. When we assessed the effects of αGlcNAc binding to MUC1, we found that αGlcNAc blocked galectin-3 binding to MUC1, phosphorylation of the MUC1 C-terminus, and recruitment of Src and ß-catenin to that C-terminus. These results suggest that αGlcNAc regulates cancer cell phenotypes by dampening MUC1 signal transduction.

MUC6 expression is a preferable prognostic marker for invasive mucinous adenocarcinoma of the lung.

Gastric gland mucin consists of core protein MUC6 with residues heavily glycosylated by unique O-glycans carrying α1,4-linked N-acetylglucosamine (αGlcNAc). αGlcNAc-glycosylated MUC6 protein is seen in normal gastric and duodenal glands. Decreased αGlcNAc glycosylation on MUC6-positive tumor cells is often observed in premalignant lesions of the stomach, pancreas, and bile duct, and decreased MUC6 expression is seen in invasive cancer of these organs. Lung cancer (LC) is the most common cause of cancer death worldwide. Recently, the adenocarcinoma subtype has become the most common histological subtype of LC, and one of its invasive forms is invasive mucinous adenocarcinoma (IMA). Currently, prognostic markers of LC IMA are unknown. Here, we analyzed MUC5AC, MUC6, and αGlcNAc expression in 54 IMA LC cases. MUC5AC was positively expressed in 50 (93%), MUC6 in 38 (70%), and αGlcNAc in 19 (35%). Each expression level was scored from 0 to 3. The αGlcNAc expression score was significantly decreased relative to MUC6 (P < 0.001). Interestingly, disease-free survival was significantly higher in MUC6-positive than MUC6-negative cases based on the log-rank test (P = 0.021). For in vitro analysis, we ectopically expressed MUC6 in A549 cells, derived from LC and harboring a KRAS mutation. MUC6-expressing A549 cells showed significantly lower proliferation, motility, and invasiveness than control cells. Finally, F-actin staining in MUC6-expressing cells revealed a decrease or loss of filopodia associated with decreased levels of FSCN transcripts, which encodes an actin-bundling protein fascin1 necessary for cell migration. We conclude that MUC6 expression is a preferable prognostic biomarker in IMA LC.

Glycosylation of MUC6 by α1,4-linked N-acetylglucosamine enhances suppression of pancreatic cancer malignancy.

Biomarkers for early diagnosis of pancreatic cancer are greatly needed, as the high fatality of this cancer is in part due to delayed detection. α1,4-linked N-acetylglucosamine (αGlcNAc), a unique O-glycan specific to gastric gland mucus, is biosynthesized by α1,4-N-acetylglucosaminyltransferase (α4GnT) and primarily bound at the terminal glycosylated residue to scaffold protein MUC6. We previously reported that αGlcNAc expression decreases at early stages of neoplastic pancreatic lesions, followed by decreased MUC6 expression, although functional effects of these outcomes were unknown. Here, we ectopically expressed α4GnT, the αGlcNAc biosynthetic enzyme, together with MUC6 in the human pancreatic cancer cell lines MIA PaCa-2 and PANC-1, neither of which expresses α4GnT and MUC6. We observed significantly suppressed proliferation in both lines following coexpression of α4GnT and MUC6. Moreover, cellular motility decreased following MUC6 ectopic expression, an effect enhanced by cotransduction with α4GnT. MUC6 expression also attenuated invasiveness of both lines relative to controls, and this effect was also enhanced by additional α4GnT expression. We found αGlcNAc-bound MUC6 formed a complex with trefoil factor 2. Furthermore, analysis of survival curves of patients with pancreatic ductal adenocarcinoma using a gene expression database showed that samples marked by higher A4GNT or MUC6 mRNA levels were associated with relatively favorable prognosis. These results strongly suggest that αGlcNAc and MUC6 function as tumor suppressors in pancreatic cancer and that decreased expression of both may serve as a biomarker of tumor progression to pancreatic cancer.

Cholestenone functions as an antibiotic against Helicobacter pylori by inhibiting biosynthesis of the cell wall component CGL.

Helicobacter pylori, a pathogen responsible for gastric cancer, contains a unique glycolipid, cholesteryl-α-D-glucopyranoside (CGL), in its cell wall. Moreover, O-glycans having α1,4-linked N-acetylglucosamine residues (αGlcNAc) are secreted from gland mucous cells of gastric mucosa. Previously, we demonstrated that CGL is critical for H. pylori survival and that αGlcNAc serves as antibiotic against H. pylori by inhibiting CGL biosynthesis. In this study, we tested whether a cholesterol analog, cholest-4-en 3-one (cholestenone), exhibits antibacterial activity against H. pylori in vitro and in vivo. When the H. pylori standard strain ATCC 43504 was cultured in the presence of cholestenone, microbial growth was significantly suppressed dose-dependently relative to microbes cultured with cholesterol, and cholestenone inhibitory effects were not altered by the presence of cholesterol. Morphologically, cholestenone-treated H. pylori exhibited coccoid forms. We obtained comparable results when we examined the clarithromycin-resistant H. pylori strain "2460." We also show that biosynthesis of CGL and its derivatives cholesteryl-6-O-tetradecanoyl-α-D-glucopyranoside and cholesteryl-6-O-phosphatidyl-α-D-glucopyranoside in H. pylori is remarkably inhibited in cultures containing cholestenone. Lastly, we asked whether orally administered cholestenone eradicated H. pylori strain SS1 in C57BL/6 mice. Strikingly, mice fed a cholestenone-containing diet showed significant eradication of H. pylori from the gastric mucosa compared with mice fed a control diet. These results overall strongly suggest that cholestenone could serve as an oral medicine to treat patients infected with H. pylori, including antimicrobial-resistant strains.

Cecal Tumorigenesis in Aryl Hydrocarbon Receptor-Deficient Mice Depends on Cecum-Specific Mitogen-Activated Protein Kinase Pathway Activation and Inflammation.

The aryl hydrocarbon receptor (AhR) is a transcription factor known as a dioxin receptor. Recently, Ahr-/- mice were revealed to develop cecal tumors with inflammation and Wnt/ß-catenin pathway activation. However, whether ß-catenin degradation is AhR dependent remains unclear. To determine whether other signaling pathways function in Ahr-/- cecal tumorigenesis, we investigated histologic characteristics of the tumors and cytokine/chemokine production in tumors and Ahr-/- peritoneal macrophages. AhR expression was also assessed in human colorectal carcinomas. Of the 28 Ahr-/- mice, 10 developed cecal lesions by 50 weeks of age, an incidence significantly lower than previously reported. Cecal lesions of Ahr-/- mice developed from serrated hyperplasia to adenoma/dysplasia-like neoplasia with enhanced proliferation. Macrophage and neutrophil infiltration into the lesions was also observed early in serrated hyperplasia, although adjacent mucosa was devoid of inflammation. Il1b, Il6, Ccl2, and Cxcl5 were up-regulated at lesion sites, whereas only IL-6 production increased in Ahr-/- peritoneal macrophages after lipopolysaccharide + ATP stimulation. Neither Myc (alias c-myc) up-regulation nor ß-catenin nuclear translocation was observed, unlike previously reported. Interestingly, enhanced phosphorylation of extracellular signal-regulated kinase, Src, and epidermal growth factor receptor and Amphiregulin up-regulation at Ahr-/- lesion sites were detected. In human serrated lesions, however, AhR expression in epithelial cells was up-regulated despite morphologic similarity to Ahr-/- cecal lesions. Our results suggest novel mechanisms underlying Ahr-/- cecal tumorigenesis, depending primarily on cecum-specific mitogen-activated protein kinase pathway activation and inflammation.

Analysis of A4gnt Knockout Mice Reveals an Essential Role for Gastric Sulfomucins in Preventing Gastritis Cystica Profunda.

Gastric adenocarcinoma cells secrete sulfomucins, but their role in gastric tumorigenesis remains unclear. To address that question, we generated A4gnt/Chst4 double-knockout (DKO) mice by crossing A4gnt knockout (KO) mice, which spontaneously develop gastric adenocarcinoma, with Chst4 KO mice, which are deficient in the sulfotransferase GlcNAc6ST-2. A4gnt/Chst4 DKO mice lack gastric sulfomucins but developed gastric adenocarcinoma. Unexpectedly, severe gastric erosion occurred in A4gnt/Chst4 DKO mice at as early as 3 weeks of age, and with aging these lesions were accompanied by gastritis cystica profunda (GCP). Cxcl1, Cxcl5, Ccl2, and Cxcr2 transcripts in gastric mucosa of 5-week-old A4gnt/Chst4 DKO mice exhibiting both hyperplasia and severe erosion were significantly upregulated relative to age-matched A4gnt KO mice, which showed hyperplasia alone. However, upregulation of these genes disappeared in 50-week-old A4gnt/Chst4 DKO mice exhibiting high-grade dysplasia/adenocarcinoma and GCP. Moreover, Cxcl1 and Cxcr2 were downregulated in A4gnt/Chst4 DKO mice relative to age-matched A4gnt KO mice exhibiting adenocarcinoma alone. These combined results indicate that the presence of sulfomucins prevents severe gastric erosion followed by GCP in A4gnt KO mice by transiently regulating a set of inflammation-related genes, Cxcl1, Cxcl5, Ccl2, and Cxcr2 at 5 weeks of age, although sulfomucins were not directly associated with gastric cancer development.

Annexin A1 expression is correlated with malignant potential of renal cell carcinoma.

OBJECTIVES: To evaluate the expression of annexin A1 protein in patients with renal cell carcinoma. METHODS: Annexin A1 expression was examined in renal cell carcinoma specimens from 27 patients, and their disease-free survival was analyzed using the log-rank test. Annexin A1 knockdown in the human renal cell carcinoma cell line Caki-1 was carried out, and its proliferation, invasion, motility and adhesion were compared with those of control cells. RESULTS: In 13 out of 27 patients, annexin A1 was highly expressed in the membrane of renal cell carcinoma tumor cells, whereas in the rest of the patients, annexin A1 expression was weak or negligible in the membrane of those cells. Patients with high annexin A1 expression had significantly poorer disease-free survival than those with weak or negligible annexin A1 expression (P = 0.031). In the renal cell carcinoma cell line, annexin A1 knockdown cells showed significantly decreased proliferation, invasion, motility and adhesion relative to control cells, and expressed lower relative levels of membrane-type 1 matrix metalloproteinase and hypoxia-inducible factor 1-alpha transcripts, showing a potential pathway regulated by annexin A1. CONCLUSION: Annexin A1 is associated with renal cell carcinoma malignant potential and could serve as a marker of poor prognosis.

Fascin1 suppresses RIG-I-like receptor signaling and interferon-ß production by associating with IκB kinase ϵ (IKKϵ) in colon cancer.

Fascin1 is an actin-bundling protein involved in cancer cell migration and has recently been shown also to have roles in virus-mediated immune cell responses. Because viral infection has been shown to activate immune cells and to induce interferon-ß expression in human cancer cells, we evaluated the effects of fascin1 on virus-dependent signaling via the membrane- and actin-associated protein RIG-I (retinoic acid-inducible gene I) in colon cancer cells. We knocked down fascin1 expression with shRNA retrovirally transduced into a DLD-1 colon cancer and L929 fibroblast-like cell lines and used luciferase reporter assays and co-immunoprecipitation to identify fascin1 targets. We found that intracellular poly(I·C) transfection to mimic viral infection enhances the RIG-I/MDA5 (melanoma differentiation-associated gene 5)-mediated dimerization of interferon regulatory factor 3 (IRF-3). The transfection also significantly increased the expression levels of IRF-7, interferon-ß, and interferon-inducible cytokine IP-10 in fascin1-deleted cells compared with controls while significantly suppressing cell growth, migration, and invasion. We also found that fascin1 constitutively interacts with IκB kinase ϵ (IKKϵ) in the RIG-I signaling pathway. In summary, we have identified fascin1 as a suppressor of the RIG-I signaling pathway associating with IκB kinase ϵ in DLD-1 colon cancer cells to suppress immune responses to viral infection.

Potential Role of ASC, a Proapoptotic Protein, for Determining the Cisplatin Susceptibility of Lung Cancer Cells.

Primary lung cancer is the most frequent cause of cancer-related deaths worldwide. Cisplatin has been used as a key drug in the treatment for patients with lung cancer; however, most of the patients failed to respond to cisplatin within several months, and the mechanisms underlying the cisplatin resistance have not been fully elucidated. Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) is a key adaptor protein in the formation of inflammasomes. ASC is also involved in apoptotic signaling. Importantly, ASC expression is decreased in lung cancer and various cancers, but its precise function in tumor progression remains unknown. To explore the hitherto unknown role of ASC in lung cancer, we initially searched for lung cancer cell lines with higher expression levels of ASC using Cancer Cell Line Encyclopedia (CCLE) database, thereby identifying the A549 human non-small cell lung cancer cell line. Accordingly, with retroviral shRNA, the expression of ASC was forced to decrease in A549 cells. Stable ASC-knockdown cells, thus established, showed the increased activities of proliferation, motility, and invasion, compared with control cells. Importantly, ASC-knockdown cells also became resistant to cisplatin, but not to other anti-cancer agents, 5-fluorouracil and paclitaxel. Bcl-2 and phospho-Src levels were increased in ASC-knockdown cells. A Bcl-2 inhibitor, ABT-199, induced an apoptotic response in ASC-knockdown cells, and dasatinib, a Src inhibitor, blocked cell invasiveness. Thus, ASC may be involved in tumor suppression and cell death via Bcl-2 and pSrc. Targeting Bcl-2 and Src in ASC-downregulated populations of lung cancer may improve treatment outcome.

Gastric gland mucin-specific O-glycan expression decreases with tumor progression from precursor lesions to pancreatic cancer.

Pancreatic cancer is lethal, as it is often detected late. Thus, novel biomarkers of precursor lesions are needed to devise timely therapies. Pancreatic intraepithelial neoplasia (PanIN) and intraductal papillary mucinous neoplasm (IPMN) are major precursors of pancreatic cancer. In normal gastric mucosa, gastric gland mucin-specific O-glycans are unique in having α1,4-linked N-acetylglucosamine (αGlcNAc) residues attached to MUC6. Recently we reported that αGlcNAc functions as a tumor suppressor for differentiated-type gastric adenocarcinoma (Karasawa et al., J Clin Invest 122, 923, 2012). MUC6 is also expressed in pancreatic neoplasms, including PanIN and IPMN, but the role of αGlcNAc expression in pancreatic neoplasms remains unknown. Here, we analyze expression patterns of αGlcNAc, MUC6 and MUC5AC in pancreatic neoplasms and compare them with progression from PanIN to invasive ductal adenocarcinoma (IDAC) (the PanIN-IDAC sequence; 20 cases) and from IPMN to IPMN with associated invasive carcinoma (IPMNAIC) (the IPMN-IPMNAIC sequence; 20 cases). At both sequences, the frequency of MUC6-positive and αGlcNAc-positive lesions decreased with tumor progression. We then compared expression levels of αGlcNAc and MUC6 at each step of the progression. At the PanIN-IDAC sequence, αGlcNAc expression significantly decreased relative to MUC6 in low-grade PanIN (P = 0.021), high-grade PanIN/intraductal spread of IDAC (P = 0.031) and IDAC (P = 0.013). At the IPMN-IPMNAIC sequence, decreased αGlcNAc expression was also observed in low-grade IPMN exhibiting gastric-type morphology (P = 0.020). These results suggest that decreased expression of αGlcNAc relative to MUC6 occurs early and marks the initiation of tumor progression to pancreatic cancer.

ASC Induces Apoptosis via Activation of Caspase-9 by Enhancing Gap Junction-Mediated Intercellular Communication.

ASC (apoptosis-associated speck-like protein containing a CARD) is a key adaptor molecule of inflammasomes that mediates inflammatory and apoptotic signals. Aberrant methylation-induced silencing of ASC has been observed in a variety of cancer cells, thus implicating ASC in tumor suppression, although this role remains incompletely defined especially in the context of closely neighboring cell proliferation. As ASC has been confirmed to be silenced by abnormal methylation in HT1080 fibrosarcoma cells as well, this cell line was investigated to characterize the precise role and mechanism of ASC in tumor progression. The effects of ASC were examined using in vitro cell cultures based on comparisons between low and high cell density conditions as well as in a xenograft murine model. ASC overexpression was established by insertion of the ASC gene into pcDNA3 and pMX-IRES-GFP vectors, the latter being packed into a retrovirus and subjected to reproducible competitive assays using parental cells as an internal control, for evaluation of cell viability. p21 and p53 were silenced using shRNA. Cell viability was suppressed in ASC-expressing transfectants as compared with control cells at high cell density conditions in in vitro culture and colony formation assays and in in vivo ectopic tumor formation trials. This suppression was not detected in low cell density conditions. Furthermore, remarkable progression of apoptosis was observed in ASC-introduced cells at a high cell density, but not at a low one. ASC-dependent apoptosis was mediated not by p21, p53, or caspase-1, but rather by cleavage of caspase-9 as well as by suppression of the NF-κB-related X-linked inhibitor-of-apoptosis protein. Caspase-9 cleavage was observed to be dependent on gap junction formation. The remarkable effect of ASC on the induction of apoptosis through caspase-9 and gap junctions revealed in this study may lead to promising new approaches in anticancer therapy.

Novel role of ASC as a regulator of metastatic phenotype.

Disorders of cytoskeletal remodeling and signal transduction are frequently involved in cancer progression. In particular, apoptosis-associated speck-like protein containing a caspase-recruitment domain (ASC) has been reported a proapoptotic molecule that is epigenetically silenced in several human cancers. ASC is a well-characterized adaptor protein involved in the formation of multiprotein oligomers, called inflammasomes, and plays a crucial role in the activation and secretion of interleukin-1ß and interleukin-18 in innate immune cells. However, the function of ASC in the regulation of tumor progression remains elusive. The present investigation examined the involvement of ASC in cancer progression and the acquisition of metastatic ability. To determine the effect of ASC depletion in in vitro and in vivo model systems, ASC was stably knocked down in B16 murine melanoma cell lines using retroviral transduction of shRNA. ASC suppression increased the motility of B16BL6 cells in scratch assays and augmented invasiveness as assessed by a Matrigel-coated transwell system. Invadopodia formation and Src phosphorylation level were markedly enhanced in ASC-knockdown cells as well. Since caspase-8 has been reported to enhance cellular migration by Tyr380 phosphorylation via Src, we examined Tyr380 phosphorylation of caspase-8 in ASC-knockdown cells and found it to be elevated in ASC-knockdown cells but attenuated by z-VAD-fmk or z-IETD-fmk. Moreover, ASC ablation increased pulmonary metastasis in mice after intravenous injection of B16BL6 cells. Our cumulative findings indicate that ASC suppresses cancer metastasis and progression via the modulation of cytoskeletal remodeling and the Src-caspase-8 signaling pathway.

Blocking TNF-alpha in mice reduces colorectal carcinogenesis associated with chronic colitis.

The inflammatory bowel disease ulcerative colitis (UC) frequently progresses to colon cancer. To understand the mechanisms by which UC patients develop colon carcinomas, we used a mouse model of the disease whereby administration of azoxymethane (AOM) followed by repeated dextran sulfate sodium (DSS) ingestion causes severe colonic inflammation and the subsequent development of multiple tumors. We found that treating WT mice with AOM and DSS increased TNF-alpha expression and the number of infiltrating leukocytes expressing its major receptor, p55 (TNF-Rp55), in the lamina propria and submucosal regions of the colon. This was followed by the development of multiple colonic tumors. Mice lacking TNF-Rp55 and treated with AOM and DSS showed reduced mucosal damage, reduced infiltration of macrophages and neutrophils, and attenuated subsequent tumor formation. WT mice transplanted with TNF-Rp55-deficient bone marrow also developed significantly fewer tumors after AOM and DSS treatment than either WT mice or TNF-Rp55-deficient mice transplanted with WT bone marrow. Furthermore, administration of etanercept, a specific antagonist of TNF-alpha, to WT mice after treatment with AOM and DSS markedly reduced the number and size of tumors and reduced colonic infiltration by neutrophils and macrophages. These observations identify TNF-alpha as a crucial mediator of the initiation and progression of colitis-associated colon carcinogenesis and suggest that targeting TNF-alpha may be useful in treating colon cancer in individuals with UC.

Aberrant Pim-3 expression is involved in gastric adenoma-adenocarcinoma sequence and cancer progression.

PURPOSE: Pim-3, a member of the proto-oncogene Pim family with serine/threonine kinase activity was aberrantly expressed in cancerous lesions of endoderm-derived organs such as liver, pancreas, and colon. The aim of this study was to clarify the role of Pim-3 expression in the tumorigenesis and the development of gastric carcinomas. METHODS: Pim-3 expression was immunohistochemically examined on the tissue microarrays containing primary (n = 285) and metastastic (n = 37) sites of gastric carcinomas, in comparison with adenoma (n = 48) and non-cancerous mucosa (n = 84). It was also compared with the clinicopathological parameters of gastric carcinomas. RESULTS: Pim-3 expression was enhanced in adenoma (64.6%) and metastasis sites of gastric carcinoma (73.0%), to a lesser degree in primary sites of gastric carcinoma (39.3%) when compared to non-cancerous mucosa (13.1%, p < 0.0001). Pim-3 expression levels were higher in intestinal-type than diffuse-type gastric carcinoma (p = 0.018). Pim-3 expression was closely correlated with sex (p = 0.047), lymphatic (p = 0.019) and venous invasion (p = 0.014). Pim-3 expression was correlated significantly with vascular endothelial growth factor (VEGF, p = 0.009) and extracellular matrix metalloproteinase inducer (EMMPRIN, p = 0.032), both of which are presumed to be involved in neovascularization, a crucial step for metastasis. On the contrary, phosphatase and tensin homology deleted from human chromosome 10 (Pten) negative gastric carcinomas exhibited higher Pim-3 expression than Pten positive ones (p = 0.042). There was no relationship between Pim-3 expression and MVD in gastric carcinomas (p = 0.715). Furthermore, patients with Pim-3 positive gastric cancer, showed a lower cumulative survival rate than those with Pim-3 negative gastric cancer (p = 0.014) and Pim-3 positive was also identified as an independent prognostic factor for gastric carcinoma patients (p = 0.006). CONCLUSIONS: Aberrant Pim-3 expression was involved in gastric adenoma-adenocarcinoma sequence and subsequent invasion and metastasis process in gastric cancer. Moreover, Pim-3 may be employed to predict the prognosis of gastric cancer patients. Distinct Pim-3 expression underlies the molecular mechanisms for the differentiation of intestinal-type and diffuse-type carcinomas.

Proto-oncogene, Pim-3 with serine/threonine kinase activity, is aberrantly expressed in human colon cancer cells and can prevent Bad-mediated apoptosis.

We previously observed that Pim-3 with serine/threonine kinase activity, was aberrantly expressed in malignant lesions of endoderm-derived organs, liver and pancreas. Because Pim-3 protein was not detected in normal colon mucosal tissues, we evaluated Pim-3 expression in malignant lesions of human colon, another endoderm-derived organ. Pim-3 was detected immunohistochemically in well-differentiated (43/68 cases) and moderately differentiated (23/41 cases) but not poorly differentiated colon adenocarcinomas (0/5 cases). Moreover, Pim-3 proteins were detected in adenoma (35/40 cases) and normal mucosa (26/111 cases), which are adjacent to adenocarcinoma. Pim-3 was constitutively expressed in SW480 cells and the transfection with Pim-3 short hairpin RNA promoted apoptosis. In the same cell line, a pro-apoptotic molecule, Bad, was phosphorylated at Ser(112) and Ser(136) sites of phosphorylation that are representative of its inactive form. Ser(112) but not Ser(136) phosphorylation in this cell line was abrogated by Pim-3 knockdown. Furthermore, in human colon cancer tissues, Pim-3 co-localized with Bad in all cases (9/9) and with phospho-Ser(112)Bad in most cases (6/9). These observations suggest that Pim-3 can inactivate Bad by phosphorylating its Ser(112) in human colon cancer cells and thus may prevent apoptosis and promote progression of human colon cancer.