Ryunosuke Kogo

Long Noncoding RNA HOTAIR Regulates Polycomb-Dependent Chromatin Modification and Is Associated with Poor Prognosis in Colorectal Cancers

The functional impact of recently discovered long noncoding RNAs (ncRNAs) in human cancer remains to be clarified. One long ncRNA which has attracted attention is the Hox transcript antisense intergenic RNA termed HOTAIR, a long ncRNA expressed from the developmental HOXC locus located on chromosome 12q13.13. In cooperation with Polycomb complex PRC2, the HOTAIR long ncRNA is reported to reprogram chromatin organization and promote breast cancer metastasis. In this study, we examined the status and function of HOTAIR in patients with stage IV colorectal cancer (CRC) who have liver metastases and a poor prognosis. HOTAIR expression levels were higher in cancerous tissues than in corresponding noncancerous tissues and high HOTAIR expression correlated tightly with the presence of liver metastasis. Moreover, patients with high HOTAIR expression had a relatively poorer prognosis. In a subset of 32 CRC specimens, gene set enrichment analysis using cDNA array data revealed a close correlation between expression of HOTAIR and members of the PRC2 complex (SUZ12, EZH2, and H3K27me3). Our findings suggest that HOTAIR expression is associated with a genome-wide reprogramming of PRC2 function not only in breast cancer but also in CRC, where upregulation of this long ncRNA may be a critical element in metastatic progression.

Clinical significance of the expression of long non-coding RNA HOTAIR in primary hepatocellular carcinoma.

The functions of many long non-coding RNAs (ncRNAs) in human cancers have not yet been elucidated. The long ncRNA HOTAIR is expressed from the developmental HOXC locus located on chromosome 12q13.13. Previous reports have demonstrated that HOTAIR associates with chromatin modifications in cooperation with the Polycomb complex PRC2, and promotes breast and colorectal cancer metastasis. In this study, we examined the clinical significance of HOTAIR expression in patients with hepatocellular carcinoma (HCC). HOTAIR expression was detected in primary HCCs in 13 out of 64 patients. Patients with HOTAIR expression had significantly poorer prognoses and a larger primary tumor size than those without HOTAIR expression, similar to studies in breast and colorectal cancers. Moreover, introduction of human HOTAIR into liver cancer cells revealed that HOTAIR promoted more rapid proliferation compared to control cells. Thus, although the clinical significance of HOTAIR expression in HCC may not be as pronounced as that in breast and colorectal cancers, the current study demonstrates that HOTAIR expression is associated with HCC progression, warranting further studies.

Clinical Significance of miR-146a in Gastric Cancer Cases

Purpose: The profiles of microRNAs change significantly in gastric cancer. MiR-146a is reported to be a tumor suppressor in pancreatic cancer, breast cancer, and prostate cancer. We investigated the clinical significance of miR-146a in gastric cancer, in particular focusing on hypothetical miR-146a target genes, such as epidermal growth factor receptor (EGFR) and interleukin-1 receptor-associated kinase (IRAK1). Experimental Design: We examined miR-146a levels in 90 gastric cancer samples by q-real-time (qRT)–PCR and analyzed the association between miR-146a levels and clinicopathologic factors and prognosis. The regulation of EGFR and IRAK1 by miR-146a was examined with miR-146a–transfected gastric cancer cells. Moreover, we analyzed the association between miR-146a levels and the G/C single nucleotide polymorphism (SNP) within pre-miR-146a seed sequences in 76 gastric cancer samples, using direct sequencing of genomic DNA. Results: In 90 clinical samples of gastric cancer, miR-146a levels in cancer tissues were significantly lower than those in the corresponding noncancerous tissue (P < 0.001). Lower levels of miR-146a were associated with lymph node metastasis and venous invasion (P < 0.05). Moreover, a lower level of miR-146a was an independent prognostic factor for overall survival (P = 0.003). Ectopic expression of miR-146a inhibited migration and invasion and downregulated EGFR and IRAK1 expression in gastric cancer cells. In addition, G/C SNP within the pre-miR-146a seed sequence significantly reduced miR-146a levels in the GG genotype compared with the CC genotype. Conclusions:MiR-146a contains an SNP, which is associated with mature miR-146a expression. MiR-146a targeting of EGFR and IRAK1 is an independent prognostic factor in gastric cancer cases. Clin Cancer Res; 17(13); 4277–84. ©2011 AACR.

Plastin3 Is a Novel Marker for Circulating Tumor Cells Undergoing the Epithelial–Mesenchymal Transition and Is Associated with Colorectal Cancer Prognosis

Circulating tumor cells (CTC) in blood have attracted attention both as potential seeds for metastasis and as biomarkers. However, most CTC detection systems might miss epithelial-mesenchymal transition (EMT)-induced metastatic cells because detection is based on epithelial markers. First, to discover novel markers capable of detecting CTCs in which EMT has not been repressed, microarray analysis of 132 colorectal cancers (CRC) from Japanese patients was conducted, and 2,969 genes were detected that were overexpressed relative to normal colon mucosa. From the detected genes, we selected those that were overexpressed CRC with distant metastasis. Then, we analyzed the CRC metastasis-specific genes (n = 22) to determine whether they were expressed in normal circulation. As a result, PLS3 was discovered as a CTC marker that was expressed in metastatic CRC cells but not in normal circulation. Using fluorescent immunocytochemistry, we validated that PLS3 was expressed in EMT-induced CTC in peripheral blood from patients with CRC with distant metastasis. PLS3-expressing cells were detected in the peripheral blood of approximately one-third of an independent set of 711 Japanese patients with CRC. Multivariate analysis showed that PLS3-positive CTC was independently associated with prognosis in the training set (n = 381) and the validation set [n = 330; HR = 2.17; 95% confidence interval (CI) = 1.38-3.40 and HR = 3.92; 95% CI = 2.27-6.85]. The association between PLS3-positive CTC and prognosis was particularly strong in patients with Dukes B (HR = 4.07; 95% CI = 1.50-11.57) and Dukes C (HR = 2.57; 95% CI = 1.42-4.63). PLS3 is a novel marker for metastatic CRC cells, and it possesses significant prognostic value.

Regulation of the MDM2-P53 pathway and tumor growth by PICT1 via nucleolar RPL11

PICT1 (also known as GLTSCR2) is considered a tumor suppressor because it stabilizes phosphatase and tensin homolog (PTEN), but individuals with oligodendrogliomas lacking chromosome 19q13, where PICT1 is located, have better prognoses than other oligodendroglioma patients. To clarify the function of PICT1, we generated Pict1-deficient mice and embryonic stem (ES) cells. Pict1 is a nucleolar protein essential for embryogenesis and ES cell survival. Even without DNA damage, Pict1 loss led to p53-dependent arrest of cell cycle phase G1 and apoptosis. Pict1-deficient cells accumulated p53, owing to impaired Mdm2 function. Pict1 binds Rpl11, and Rpl11 is released from nucleoli in the absence of Pict1. In Pict1-deficient cells, increased binding of Rpl11 to Mdm2 blocks Mdm2-mediated ubiquitination of p53. In human cancer, individuals whose tumors express less PICT1 have better prognoses. When PICT1 is depleted in tumor cells with intact P53 signaling, the cells grow more slowly and accumulate P53. Thus, PICT1 is a potent regulator of the MDM2-P53 pathway and promotes tumor progression by retaining RPL11 in the nucleolus.

A new PICTure of nucleolar stress

Cell growth demands new protein synthesis, which requires nucleolar ribosomal functions. Ribosome biogenesis consumes a large proportion of the cells resources and energy, and so is tightly regulated through an intricate signaling network to guarantee fidelity. Thus, events that impair ribosome biogenesis cause nucleolar stress. In response to this stress, several nucleolar ribosomal proteins (RPs) translocate to the nucleoplasm and bind to MDM2. MDM2‐mediated ubiquitination and degradation of the tumor suppressor p53 is then blocked, resulting in p53 accumulation and the induction of p53‐dependent cell cycle arrest and apoptosis. Nucleolar stress is therefore a quality control surveillance mechanism that monitors the synthesis and assembly of the rRNA and protein components of ribosomes. Although nucleolar stress signaling pathways have been extensively analyzed, critical questions remain about their regulatory mechanisms. For example, how do RPs translocate from the nucleolus to the nucleoplasm to exert their functions, and do these p53‐regulating RPs influence the prognosis of human cancer patients? Our laboratory recently identified the nucleolar protein PICT1 as a novel regulator of nucleolar stress. PICT1 sequesters the ribosomal protein RPL11 in the nucleolus, preventing it from binding to MDM2. MDM2 is then free to degrade p53, favoring tumor cell growth. Accordingly, the level of PICT1 in a tumor is becoming a useful prognostic marker for human cancers. This review summarizes the evidence that links nucleolar stress to tumorigenesis, and casts PICT1 as an oncogenic player in human cancer biology. (Cancer Sci 2012; 103: 632–637)

Correlations between thymidylate synthase expression and chemosensitivity to 5-fluorouracil, cell proliferation and clinical outcome in head and neck squamous cell carcinoma

Background: 5-Fluorouracil (5-FU) is a widely used drug in head and neck squamous cell carcinoma (HNSCC). Thymidylate synthase (TS), which is the target enzyme of 5-FU, has been demonstrated to be a key regulatory enzyme. In this study, we examined whether TS expression is correlated with chemosensitivity to 5-FU, cell proliferation and clinical outcome in HNSCC. Methods: An antisense TS cDNA was constitutively expressed in the HNSCC cell line. The effects of TS expression on in vitro cell growth and 5-FU cytotoxicity were examined. We also evaluated the association between TS expression and cell proliferation in surgical specimens, and prognosis in HNSCC patients. Results: Antisense TS transfection increases the cytotoxicity of 5-FU and inhibits cell proliferation in HNSCC cellsin vitro. Immunohistochemical expression of TS may have prognostic value in patients with HNSCC. Conclusions: These results indicate that TS expression plays an important role in the sensitivity of HNSCC to 5-FU chemotherapy.

FBXO31 determines poor prognosis in esophageal squamous cell carcinoma

Cyclin D1 plays important roles in esophageal squamous cell carcinoma (ESCC) cases by amplification of the 11q13.3 locus. FBXO31 is a subunit of the SCF ubiquitin ligase, which targets cyclin D1 for degradation. In this study, we clarified the clinical significance of FBXO31 and characterized the association between cyclin D1 and FBXO31 in ESCC cases. Total RNA was extracted from tumor tissues obtained from 68 ESCC patients who underwent surgical resection. FBXO31 expression levels were determined by quantitative RT-PCR, and both FBXO31 and cyclin D1 protein expression and localization were evaluated by immunohistochemistry (IHC). Furthermore, using CGH and gene expression array data of another subset, we validated the association between cyclin D1 genomic amplification and FBXO31 expression levels. Higher FBXO31 expression levels significantly correlated with depth of tumor invasion and clinical stage (P<0.05). In addition, the FBXO31 high expression group showed a significantly poorer prognosis than the low expression group (P<0.001). Multivariate analysis indicated that FBXO31 expression was an independent prognostic factor [relative risk (RR): 1.79, confidence interval (CI): 1.14-3.01, P=0.01]. Using IHC, concordant expression was observed between cyclin D1 and FBXO31 in the nucleus and cytoplasm, respectively. CGH array indicated that cases having cyclin D1 with increased copy number were significantly associated with elevated FBXO31 expression levels (P<0.05). FBXO31 could be a novel and robust prognostic marker for ESCC.

Histone deacetylase 1 expression in gastric cancer

The aim of this study was to identify and evaluate novel prognostic markers for gastric cancer. Differential mRNA displays comparing paired tumor/normal stomach samples were assessed. Several differentially expressed cDNA fragments of candidate genes were identified, and one of these was further studied using quantitative reverse transcription-PCR in 140 human gastric carcinomas. To evaluate protein expression, immunohistochemical staining was performed in selected cases. One of the genes abundantly expressed in tumor tissue on the differential mRNA displays was identified as histone deacetylase 1 (HDAC). HDAC was overexpressed in the tumor tissue in 77% of the cases as determined by quantitative reverse transcription-PCR. Immunohistochemical staining revealed analogous results, showing strong expression in cancer cells. Patients were then classified into high (n=78) and low (n=62) expression groups according to the mean value of HDAC expression. High frequencies of lymph vessel and vascular vessel permeations, and advanced stage of the disease were recognized in the high expression group compared to the low expression group (p<0.05). Prognosis was significantly worse for the high expression group than for the low expression group (p<0.05), and multi-variate analysis demonstrated that HDAC expression was an independent prognostic factor. Although not significantly different, lymph node metastasis was recognized more frequently in the high expression group (p=0.07). In conclusion, the findings show that HDAC expression is associated with aggressive behavior of primary gastric cancer, and imply that determination of the HDAC expression status is useful for predicting prognosis in patients with gastric cancer.

PICT1 regulates TP53 via RPL11 and is involved in gastric cancer progression.

Background:The TP53 pathway is frequently inactivated in human cancers. PICT1 (also known as GLTSCR2) is a novel regulator of the MDM2-TP53 pathway via its interaction with the ribosomal protein RPL11 in the nucleolus. However, the clinical significance of PICT1 in gastric cancer remains unknown.Methods:To evaluate PICT1 function, we used shRNA to inhibit PICT1 expression in gastric cancer cells that expressed wild-type TP53. PICT1 expression and TP53 mutation status were quantified in 110 cases of primary gastric cancer to explore the impact of PICT1 expression levels on gastric cancer.Results:Deficiency of PICT1 significantly impaired cell proliferation and colony formation via TP53-mediated cell cycle arrest. Following induction of PICT1 deficiency, RPL11 translocated out of the nucleolus. Of the 110 gastric cancer samples tested, 70 (63.6%) and 40 (36.4%) tumours expressed wild-type and mutant TP53, respectively. In gastric cancer patients with wild-type TP53 tumours, patients with relatively low PICT1 expression levels had a better prognosis compared with high expression level patients (P=0.046).Conclusion:The findings suggest that PICT1 has a crucial role in gastric cancer progression by regulating the MDM2-TP53 pathway through RPL11. Clinically, PICT1 expression is a novel prognostic parameter in gastric cancer patients with wild-type TP53 tumours.