Identification and characterization of a novel human hepatocellular carcinoma-associated gene

MOB (Mps one Binder) Proteins in the Hippo Pathway and Cancer

The family of MOBs (monopolar spindle-one-binder proteins) is highly conserved in the eukaryotic kingdom. MOBs represent globular scaffold proteins without any known enzymatic activities. They can act as signal transducers in essential intracellular pathways. MOBs have diverse cancer-associated cellular functions through regulatory interactions with members of the NDR/LATS kinase family. By forming additional complexes with serine/threonine protein kinases of the germinal centre kinase families, other enzymes and scaffolding factors, MOBs appear to be linked to an even broader disease spectrum. Here, we review our current understanding of this emerging protein family, with emphases on post-translational modifications, protein-protein interactions, and cellular processes that are possibly linked to cancer and other diseases. In particular, we summarise the roles of MOBs as core components of the Hippo tissue growth and regeneration pathway.

Gene-expression signature of vascular invasion in hepatocellular carcinoma

BACKGROUND & AIMS

Vascular invasion is a major predictor of tumor recurrence after surgical treatments for hepatocellular carcinoma (HCC). While macroscopic vascular invasion can be detected by radiological techniques, pre-operative detection of microscopic vascular invasion, which complicates 30-40% of patients with early tumors, remains elusive.

METHODS

A total of 214 patients with hepatocellular carcinoma who underwent resection were included in the study. By using genome-wide gene-expression profiling of 79 hepatitis C-related hepatocellular carcinoma samples (training set), a gene-expression signature associated with vascular invasion was defined. The signature was validated in formalin-fixed paraffin-embedded tissues obtained from an independent set of 135 patients with various etiologies.

RESULTS

A 35-gene signature of vascular invasion was defined in the training set, predicting vascular invasion with an accuracy of 69%. The signature was independently associated with the presence of vascular invasion (OR 3.38, 95% CI 1.48-7.71, p=0.003) along with tumor size (diameter greater than 3 cm, OR 2.66, 95% CI 1.17-6.05, p=0.02). In the validation set, the signature discarded the presence of vascular invasion with a negative predictive value of 0.77, and significantly improved the diagnostic power of tumor size alone (p=0.045).

CONCLUSIONS

The assessment of a gene-expression signature obtained from resected biopsied tumor specimens improved the diagnosis of vascular invasion beyond clinical variable-based prediction. The signature may aid in candidate selection for liver transplantation, and guide the design of clinical trials with experimental adjuvant therapies.

MOB control: reviewing a conserved family of kinase regulators

The family of Mps One binder (MOB) co-activator proteins is highly conserved from yeast to man. At least two different MOB proteins have been identified in every eukaryote analysed to date. Initially, yeast genetics revealed essential roles for Mob1p and Mob2p in the regulation of mitotic exit and cell morphogenesis. Studies in flies then showed that dMOB1/MATS is a core component of Hippo signalling. Loss of dMOB1 resulted in increased cell proliferation and decreased cell death, suggesting that MOB1 acts as tumour suppressor protein. Recent work focused primarily on mammalian cells has shown how hMOB1 can regulate NDR/LATS kinases, a function that can to be counteracted by hMOB2. Here we summarise and discuss our current knowledge of this emerging protein family, with emphasis on subcellular localisation, protein-protein interactions and biological functions in apoptosis, mitosis, morphogenesis, cell proliferation and centrosome duplication.

Frequent alteration of the Yin Yang 1/Raf-1 kinase inhibitory protein ratio in hepatocellular carcinoma

The transcription factor Yin Yang 1 (YY1) can favor several aspects of tumorigenesis. In turn, Raf-1 Kinase Inhibitor Protein (RKIP) inhibits the oncogenic activities of MAPK and NF-κB pathways and promotes drug-induced apoptosis. Mutual influences between YY1 and RKIP may exist, and there are already separate evidences that relevant increases in YY1 and reductions in RKIP occur in hepatocellular carcinoma (HCC). However, the levels of the two factors have never been concomitantly examined in HCC. We evaluated by RT-PCR the mRNA levels of YY1, YY1AP, RKIP, and survivin in 35 clinical HCCs (91% HCV-related), in their adjacent cirrhotic tissues and in 6 healthy livers. Immunohistochemical analyses were also performed. The ratio of YY1 to RKIP mRNA was constantly profoundly inverted in the tumors compared with the adjacent nontumoral tissues. A similar result occurred frequently at protein level. Hyperactivation of YY1 in tumors was corroborated by its nuclear localization and the finding that in the tumors there were also increases in YY1AP, a YY1 coactivator not expressed in normal liver, and in survivin, as a possible target of YY1. The frequent alteration in the YY1-RKIP balance might represent a marker of malignant progression and be exploited for therapeutic interventions in HCC.

Hepatocellular carcinoma-associated gene 2 interacts with MAD2L2

HCCA2 (hepatocellular carcinoma-associated gene 2) was initially identified as a HCC (hepatocellular carcinoma)-specific protein and subsequently, a long splice variant of HCCA2 was identified as a co-activator of transcription factor YY1 (Yin Yang 1). To investigate the role of HCCA2 in HCC genesis and progression, we screened a human fetal liver cDNA library and identified a novel HCCA2-interacting protein, MAD2L2 (MAD2 mitotic arrest deficient-like 2 (yeast)). The interaction between HCCA2 and MAD2L2 was confirmed by in vitro and in vivo binding assays and the interaction domain was mapped to the N-terminus of HCCA2 by sequential deletion. HCCA2 and MAD2L2 also colocalized in the nucleus of Hela cells. Furthermore, overexpression of HCCA2 led to cell cycle arrest at G0/G1 phase and therefore inhibited cell proliferation. Our research suggests that HCCA2 may play a novel role in cell cycle regulation.

HTPAP gene on chromosome 8p is a candidate metastasis suppressor for human hepatocellular carcinoma

Our previous studies suggested that chromosome 8p deletion is associated with metastasis of hepatocellular carcinoma (HCC), in which some novel metastasis suppressor genes might be harbored. The present study aimed to identify the metastatic suppressor gene(s). A cDNA chip was constructed with the expressed sequence tags (ESTs) from chromosome 8p and used to compare the difference of expression profiling between the MHCC97-H and MHCC97-L cell lines with different metastatic potentials and similar genetic backgrounds. In all, 10 ESTs were significantly downregulated in MHCC97-H cell line with higher metastatic potential. One full-length gene, HTPAP (phosphatidic acid phosphatase type 2 domain containing 1B), was identified at chromosome 8p12. Sequencing and bioinformatic analyses revealed that HTPAP has 826 bp and encodes a putative protein of 175 amino acids with a transmembrane segment at the NH2 terminus, two protein kinase C phosphorylation site and one tyrosine kinase phosphorylation site. Its expression level in metastatic tumor tissues was much lower than that of primary HCC tissues. Both in vitro and in vivo assays suggested that HTPAP could suppress the invasion and metastasis of HCC. These suggested that HTPAP is a novel metastatic suppressor gene for HCC. The mechanism of the effect of HTPAP on HCC metastasis is not clear yet and deserves further investigation.

Transcription factor YY1: structure, function, and therapeutic implications in cancer biology

The ubiquitous transcription factor Yin Yang 1 (YY1) is known to have a fundamental role in normal biologic processes such as embryogenesis, differentiation, replication, and cellular proliferation. YY1 exerts its effects on genes involved in these processes via its ability to initiate, activate, or repress transcription depending upon the context in which it binds. Mechanisms of action include direct activation or repression, indirect activation or repression via cofactor recruitment, or activation or repression by disruption of binding sites or conformational DNA changes. YY1 activity is regulated by transcription factors and cytoplasmic proteins that have been shown to abrogate or completely inhibit YY1-mediated activation or repression; however, these mechanisms have not yet been fully elucidated. Since expression and function of YY1 are known to be intimately associated with progression through phases of the cell cycle, the physiologic significance of YY1 activity has recently been applied to models of tumor biology. The majority of the data are consistent with the hypothesis that YY1 overexpression and/or activation is associated with unchecked cellular proliferation, resistance to apoptotic stimuli, tumorigenesis and metastatic potential. Studies involving hematopoetic tumors, epithelial-based tumors, endocrine organ malignancies, hepatocellular carcinoma, and retinoblastoma support this hypothesis. Molecular mechanisms that have been investigated include YY1-mediated downregulation of p53 activity, interference with poly-ADP-ribose polymerase, alteration in c-myc and nuclear factor-kappa B (NF-kappaB) expression, regulation of death genes and gene products, and differential YY1 binding in the presence of inflammatory mediators. Further, recent findings implicate YY1 in the regulation of tumor cell resistance to chemotherapeutics and immune-mediated apoptotic stimuli. Taken together, these findings provide strong support of the hypothesis that YY1, in addition to its regulatory roles in normal biologic processes, may possess the potential to act as an initiator of tumorigenesis and may thus serve as both a diagnostic and prognostic tumor marker; furthermore, it may provide an effective target for antitumor chemotherapy and/or immunotherapy.

An anthropoid-specific segmental duplication on human chromosome 1q22

Segmental duplications (SDs) play a key role in genome evolution by providing material for gene diversification and creation of variant or novel functions. They also mediate recombinations, resulting in microdeletions, which have occasionally been associated with human genetic diseases. Here, we present a detailed analysis of a large genomic region (about 240 kb), located on human chromosome 1q22, that contains a tandem SD, SD1q22. This duplication occurred about 37 million years ago in a lineage leading to anthropoid primates, after their separation from prosimians but before the Old and New World monkey split. We reconstructed the hypothetical unduplicated ancestral locus and compared it with the extant SD1q22 region. Our data demonstrate that, as a consequence of the duplication, new anthropoid-specific genetic material has evolved in the resulting paralogous segments. We describe the emergence of two new genes, whose new functions could contribute to the speciation of anthropoid primates. Moreover, we provide detailed information regarding structure and evolution of the SD1q22 region that is a prerequisite for future studies of its anthropoid-specific functions and possible linkage to human genetic disorders.

Rapid cloning and expression of hepatocellular carcinoma associated cDNA fragments

AIM: To clone and characterize novel genes that might be involved in hepatocellular carcinoma.

METHODS: An EST fragment differentially expressed between hepatocellular carcinoma (HCC) and its adjacent nontumorous liver tissues had been cloned using suppression subtractive hybridization (SSH). With this approach, we identified a novel EST that consisted of 447bp. In order to gain its full-length cDNA fragment, two gene-specific primers were designed for 3'-rapid amplification of cDNA end RACE. One HCC cell line, HepG2, was maintained in the RPMI1640 media and recommended culture conditions. Total RNA was extracted from HepG2 by the SV Total RNA Isolation System (Promega). RACE reactions were prepared using the SMART^TM RACE cDNA amplification kit (Clontech). Initial amplification was carried out with gene-specific primer 3'GSP2(5'-CGCATAGT ACCAGTATCGACAAAGG-3'), followed by nested PCR using gene-specific primer 3'NGSP2(5'-TCCACATTACGGACCCGACGGATT-3'). These amplified cDNA fragments obtained from RACE were subcloned into the PMD18-T vector (TaKaRa) and sequenced by ABI PRISM377 DNA sequencer. Basic local aligment search tools were carried out using BLASTN and dbEST and nr database. Northern blot was applied to detect the expression of these cDNA fragments between HCC and its adjacent nontumorous liver tissues. A total of 3 liver specimens were collected from the Southwest Hospital of Chongqing in China. The final diagnosis of HCC was confirmed by histological examination. Total RNA was extracted from either HCC or its adjacent nontumorous liver tissues in the same way. These cDNA fragments were excised from the PMD18-T vector, purified and ³²P-labeled as cDNA probes using the random primed labeling method. Northern blot was prepared by using the ExpressHyb^TM hybridization solution (Clontech) according to the protocol provided by the manufacturer. Combination of Northern blot and virtual Northern (http://www.ncbi.nlm.nih.gov/SAGE)(series analysis of gene expression, SAGE), expression of these cDNA fragments in multiple carcinoma and normal tissues were analyzed.

RESULTS: Five EST fragments (694 447-3, 724 447-3, 697 447-3, 711 447-3, 692 447-3) were cloned, including two EST fragments with ploy (A) tail (694 447-3, 724 447-3). Compared with ESTs in GeneBank, the two EST fragments with ploy (A) tail represented novel genes with a common sequence. Five EST fragments accession numbers in Genebank were CK730344, CK730345, CK730346, CK730347, CK730348, respectively. Northern blot revealed that 694 447-3, 724 447-3 presented higher expression in HCC than that in its adjacent nontumorous liver tissues. Virtual Northern blot (SAGE) revealed that 694 447-3, 724 447-3 presented higher expression in multiple cancers that contained in brain, colon, breast, lung and stomach than that in their normal tissues.

CONCLUSION: Two novel human hepatocellular carcinoma-associated cDNA fragments are identified. RACE technique is a rapid and effective method for seeking for disease related genes in specific tissues.

Human Mob Proteins Regulate the NDR1 and NDR2 Serine-Threonine Kinases

Human NDR1 (nuclear Dbf2-related) is a widely expressed nuclear serine-threonine kinase that has been implicated in cell proliferation and/or tumor progression. Here we present molecular characterization of the human NDR2 serine-threonine kinase, which shares approximately 87% sequence identity with NDR1. NDR2 is expressed in most human tissues with the highest expression in the thymus. In contrast to NDR1, NDR2 is excluded from the nucleus and exhibits a punctate cytoplasmic distribution. The differential localization of NDR1 and NDR2 suggests that each kinase may serve distinct functions. Thus, to identify proteins that interact with NDR1 or NDR2, epitope-tagged kinases were immunoprecipitated from Jurkat T-cells. Two uncharacterized proteins that are homologous to the Saccharomyces cerevisiae kinase regulators Mob1 and Mob2 were identified. We demonstrate that NDR1 and NDR2 partially colocalize with human Mob2 in HeLa cells and confirm the NDR-Mob interactions in cell extracts. Interestingly, NDR1 and NDR2 form stable complexes with Mob2, and this association dramatically stimulates NDR1 and NDR2 catalytic activity. In summary, this work identifies a unique class of human kinase-activating subunits that may be functionally analagous to cyclins.

YY1AP, a novel co-activator of YY1

With the aim of identifying potential cellular proteins that mediate the transcriptional regulation of YY1, a HeLa cDNA library was screened using the yeast two-hybrid system. A previously unknown protein interacting with YY1 was identified and named YY1AP. By using the 5'-rapid amplification of cDNA ends technique, the full-length cDNA of YY1AP was cloned and sequenced. The cDNA was 2253 bp in length and encoded an open reading frame of 750 amino acids. The chromosomal gene was made up of 10 exons separated by nine introns and is localized on chromosome 1 (1q21.3). Northern blot analysis revealed that YY1AP is ubiquitously expressed in various human tissues and cancer cell lines. Co-immunoprecipitation and immunostaining of cells further indicated that YY1AP co-localizes with YY1 in the nucleus. Furthermore, YY1AP was shown to be capable of enhancing the transcriptional activation of an YY1 responsive promoter. Subsequent analysis by glutathione S-transferase pull-down assay showed that YY1AP contained two YY1 binding regions. The transactivation region of YY1AP would seem to be localized within the section of amino acids 260-345. It is proposed that YY1AP is a novel co-activator of YY1.

Antisense overexpression of BMAL2 enhances cell proliferation

To identify genes that are frequently downregulated in hepatocellular carcinoma (HCC), a panel of putative underexpressed genes was first established by an in-house cDNA macroarray method. Two different assays, semiquantitative RT-PCR combined with Northern analysis and customized cDNA microarray analysis, were used to screen through these genes and the results were compared. Several genes, some with unknown function, were confirmed to be downregulated by both the methods. The effect of a downregulated gene, BMAL2, on cell proliferation was examined. Overexpression of antisense BMAL2 RNA in 293EBNA cells resulted in reduced cell cycle time, increased plating efficiency in soft agar, diminished TNF-alpha-induced increment of CPP32/caspase-3 activity, and a reduced proportion of cells in the G2 phase with a concomitantly increased proportion of cells in the S phase. In conclusion, by combining three different methods, we have obtained a panel of frequently down regulated genes in HCC, including BMAL2. Antisense overexpression of BMAL2 enhances cell proliferation.

The alteration of PTEN tumor suppressor expression and its association with the histopathological features of human primary hepatocellular carcinoma

PURPOSE

Although deletions or inactivating mutations of the tumor suppressor gene PTEN (phosphatase and tensin homolog deleted on chromosome 10) are involved in the development of a variety of tumors including glioblastoma, melanoma, prostate cancer, breast cancer, endometrial cancers etc., the role of PTEN expression in human primary hepatocellular carcinoma (HCC) has not yet been clarified. The aim of this study is to investigate the involvement of PTEN mRNA and protein expression in HCC.

METHODS

The level of PTEN mRNA expression in HCC specimens was analyzed by Northern blot. PTEN poly-clonal antibody was raised by immunizing New Zealand white rabbit with (His)(6)-tagged PTEN fusion protein and characterized by Western blot. The level of PTEN protein expression was determined by immunohistochemistry. The significance of PTEN in HCC was analyzed by comparing its expression level with the clinicopathological parameters of HCC patients.

RESULTS

Four transcripts of PTEN mRNA at 5.5 kb, 4.4 kb, 2.4 kb, and 1.8 kb were detected in most para-carcinoma liver tissues, and the expression level of PTEN mRNA in carcinoma liver tissues was found to decrease significantly. The poly-clonal antibody raised against histidine-tagged fusion PTEN protein showed specific immuno-reactivity to PTEN protein. Using the specific poly-clonal antibody prepared and characterized by ourselves, we found that PTEN protein was significantly down-regulated in HCC tissues compared with paired para-carcinoma tissues. The protein expression of PTEN is negatively associated with the pathological grading and presence of cancer thrombus of HCC.

CONCLUSIONS

Down-regulation of PTEN expression may play an important role in the development of HCC and the level of PTEN expression may be a potential adjuvant parameter in forecasting the progression and prognosis of HCC patients.

Analysis of cell cycle gene expression responding to acetoxyscirpendiol isolated from Paecilomyces tenuipes

Paecilomyces tenuipes is believed to contain potential oncostatic and tumor-reducing components. Molecular mechanism, however, is poorly understood concerning the potential antitumor components and their biological function. We purified acetoxyscirpendiol (ASD) from methanolic extracts (MPT) of the fungus and tested the two compounds for the molecular profile of their antitumor potential. Using a differential display protocol, cyclin C and Mad-1 were identified as candidate genes responding to MPT. When a quantitative PCR was performed on the total RNA from MCF-7 treated by MPT or ASD, gene expressions of cyclin C and Mad-1 were greatly augmented. In terms of protein expression, cyclin C level increased up to 12 folds in response to ASD as well as MPT. Similar as MPT treatments, ASD-treated cells synthesize cyclin C as 2-4 fold compared to the control treatments. In terms of Mad-1 expression in cells treated with ASD, the level of Mad-1 expression increased up to 2.5 folds by MPT treatment. Cyclin C expression was compared with non-treated cells in various cell lines. MCF-7 cell was shown highly responsive to the MPT or ASD treatment. Taken together, these results strongly indicate that MPT contains potential antitumor components which might exert their action by modulating cell cycle-related genes such as cyclin C and Mad-1 in MCF-7. The major antioncogenic component in MPT may be ASD which modulates cyclin C and Mad-1 expression.