Identification of tumor suppressor candidate genes by physical and sequence mapping of the TSLC1 region of human chromosome 11q23

Clinical significance of soluble CADM1 as a novel marker for adult T-cell leukemia/lymphoma

Adult T-cell leukemia/leukemia (ATLL) is an aggressive peripheral T-cell malignancy, caused by infection with the human T-cell leukemia virus type 1 (HTLV-1). We recently showed that the cell adhesion molecule 1 (CADM1), a member of the immunoglobulin superfamily, is specifically and consistently overexpressed in ATLL cells, and functions as a novel cell surface marker. In this study, we first show that a soluble form of CADM1 (sCADM1) is secreted from ATLL cells by mainly alternative splicing. After developing the Alpha linked immunosorbent assay (AlphaLISA) for sCADM1, we show that plasma sCADM1 concentrations gradually increased during disease progression from indolent to aggressive ATLL. Although other known biomarkers of tumor burden such as soluble interleukin-2 receptor α (sIL-2Rα) also increased with sCADM1 during ATLL progression, multivariate statistical analysis of biomarkers revealed that only plasma sCADM1 was selected as a specific biomarker for aggressive ATLL, suggesting that plasma sCADM1 may be a potential risk factor for aggressive ATLL. In addition, plasma sCADM1 is a useful marker for monitoring response to chemotherapy as well as for predicting relapse of ATLL. Furthermore, the change in sCADM1 concentration between indolent and aggressive type ATLL was more prominent than the change in the percentage of CD4⁺CADM1⁺ ATLL cells. As plasma sCADM1 values fell within normal ranges in HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients with higher levels of serum sIL-2Rα, the measurement of sCADM1 may become a useful tool to discriminate between ATLL and other inflammatory diseases, including HAM/TSP.

The 18 kDa translocator protein influences angiogenesis, as well as aggressiveness, adhesion, migration, and proliferation of glioblastoma cells

BACKGROUND

It is known that the mitochondrial 18 kDa translocator protein (TSPO) is present in almost all peripheral tissues and also in glial cells in the brain. TSPO levels are typically enhanced in correlation with tumorigenesis of cancer cells including glioblastoma. Relevant for angiogenesis, TSPO is also present in almost all cells of the cardiovascular system.

METHODS

We studied the effect of TSPO knockdown by siRNA on various aspects of tumor growth of U118MG glioblastoma cells in two in-vivo models: a nude mouse model with intracerebral implants of U118MG glioblastoma cells and implantation of U118MG glioblastoma cells on the chorionallantoic membrane (CAM) of chicken embryos. In vitro, we further assayed the influence of TSPO on the invasive potential of U118MG cells.

RESULTS

TSPO knockdown increased tumor growth in both in-vivo models compared with the scrambled siRNA control. Angiogenesis was also increased by TSPO knockdown as determined by a CAM assay. TSPO knockdown led to a decrease in adhesion to the proteins of the extracellular matrix, including fibronectin, collagen I, collagen IV, laminin I, and fibrinogen. TSPO knockdown also led to an enhancement in the migratory capability of U118MG cells, as determined in a modified Boyden chamber. Application of the TSPO ligand 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide (PK 11195) at a concentration of 25 µmol/l in the in-vitro models yielded results similar to those obtained on TSPO knockdown. We found no effects of PK 11195 on TSPO protein expression. Interestingly, at low nmol/l concentrations (around 1 nmol/l), PK 11195 enhanced adhesion to collagen I, suggesting a bimodal concentration effect of PK 11195.

CONCLUSION

Intact TSPO appears to be able to counteract the invasive and angiogenic characteristics related to the aggressiveness of U118MG glioblastoma cells in vivo and in vitro.

Loss/Down-regulation of tumor suppressor in lung cancer 1 expression is associated with tumor progression and is a biomarker of poor prognosis in ovarian carcinoma

OBJECTIVES

The tumor suppressor in lung cancer 1 (TSLC1) has been identified as a putative tumor suppressor gene in non-small cell lung cancer. Although loss of TSLC1 has been observed in a number of human malignancies, the expression levels of TSLC1 gene in ovarian cancer and its clinical or prognostic significance have not been investigated.

METHODS

Protein expression levels of TSLC1 was explored by semiquantitative immunohistochemical staining on archival formalin-fixed, paraffin-embedded pathological specimen consisting of 30 normal ovaries, 30 ovarian cystadenomas, 40 borderline ovarian tumors, and 160 invasive ovarian carcinomas. The TSLC1 immunohistochemical staining results were then correlated with various clinicopathologic parameters and patient prognosis using various statistical models.

RESULTS

Significantly decreased, or complete loss of, protein expression of the TSLC1 gene was observed in 59% ovarian carcinomas, 45% borderline tumors, and 7% cystadenomas, but in none of the normal ovaries (0%). In ovarian carcinomas, decreased TSLC1 expression was significantly correlated with lymph node metastasis (pN, P = 0.001), distant metastasis (pM, P = 0.028), and more advanced International Federation of Gynecology and Obstetrics stages (P = 0.008). By univariate survival analysis on the ovarian carcinoma cohorts, decreased TSLC1 protein expression was significantly associated with shortened patient survival (mean: 26.9 months in tumors with complete loss of TSLC1 vs 63.1 months in tumors with significantly decreased TSLC1 vs 94.3 months in tumors with normal levels of TSLC1; P < 0.001). By multivariate analysis, TSLC1 protein expression remained as a significant and independent prognostic factor for the prediction of patient survival (P = 0.003).

CONCLUSIONS

Decreased protein expression of the TSLC1 gene might be important in conferring a more aggressive behavior in ovarian carcinoma. Thus, TSLC1 may be used as an independent prognostic molecular marker for patients with ovarian carcinoma.

Involvement of tumor suppressor in lung cancer 1 gene expression in cervical carcinogenesis

Tumor suppressor in lung cancer 1 (TSLC1) is a tumor suppressor gene in non-small cell lung cancer, and loss of TSLC1 gene expression has been observed in a number of epithelial carcinomas and cancer-derived cell lines. We analyzed TSLC1 gene expression by real-time reverse transcription-polymerase chain reaction in 39 invasive cervical carcinomas, 34 cervical intraepithelial neoplasia (CIN) IIIs, 35 CIN IIs, 32 CIN I, 36 inflammation cervical tissues, and 30 normal cervix samples. Loss of TSLC1 gene expression was observed in 30 of 39 (77%) cervical carcinomas, 25 of 34 (73%) CIN IIIs, 9 of 35 (26%) CIN IIs, and 7 of 32 (22%) CIN Is but was not found in inflammation and normal cervix samples. Compared to normal cervical tissue, loss of TSLC1 gene was significantly high in CIN IIIs and cervical cancer (P = 0.00). Moreover, loss of TSLC1 gene expression is observed at a significantly higher frequency in CIN IIIs and cervical cancers than in CIN IIs (P < 0.05). The results show that loss of TSLC1 gene expression is an early event in cervical carcinogenesis and often accompanies invasive cervical cancers.

Tslc1 (nectin-like molecule-2) is essential for spermatozoa motility and male fertility

The nectin-like molecule-2 (TSLC1) is a cell-cell adhesion molecule expressed in testicular germ cells. To directly examine the role of Tslc1 in male fertility, we generated Tslc1+/- mice that have greater than 90% reduction in Tslc1 expression. Tslc1+/- males exhibited reduced fertility and rarely transmitted the Tslc1 mutant allele, whereas Tslc1+/- females were consistently able to transmit the mutant allele. Histologic and electron microscopic analyses of the testes in Tslc1+/- mice demonstrated disruption of the junctional scaffold between germ cells and Sertoli cells. Reduced Tslc1 expression had no effect on germ cell proliferation or apoptosis. While evidence of normal spermatozoal maturation was supported by Fluorescence Activated Cell Sorting (FACS) analysis, spermatozoa from Tslc1+/- mice demonstrated markedly reduced motility without compromised viability. Collectively, these results establish an essential role for Tslc1 in spermatozoal maturation and motility, distinct from other members of the nectin family.

Bioinformatic characterization of the SynCAM family of immunoglobulin-like domain-containing adhesion molecules

SynCAM 1 (synaptic cell adhesion molecule 1, alternatively named Tslc1 and nectin-like protein 3) belongs to the immunoglobulin superfamily and is an adhesion molecule that operates in a variety of important contexts. Exemplary are its roles in adhesion at synapses in the central nervous system and as tumor suppressor. Here, I describe a family of genes homologous to SynCAM 1 comprising four genes found solely in vertebrates. All SynCAM genes encode proteins with three immunoglobulin-like domains of the V-set, C1-set, and I-set subclasses. Comparison of genomic with cDNA sequences provides their exon-intron structure. Alternative splicing generates isoforms of SynCAM proteins, and diverse SynCAM 1 and 2 isoforms are created in an extracellular region rich in predicted O-glycosylation sites. Protein interaction motifs in the cytosolic sequence are highly conserved among all four SynCAM proteins, indicating their critical functional role. These findings aim to facilitate the understanding of SynCAM genes and provide the framework to examine the physiological functions of this family of vertebrate-specific adhesion molecules.

Cloning and characterization of hepaCAM, a novel Ig-like cell adhesion molecule suppressed in human hepatocellular carcinoma

BACKGROUND/AIMS

Previously, we reported on gene HEPN1 that was silenced in hepatocellular carcinoma (HCC) and its capability of arresting cell growth. In this study, we identified another novel gene hepaCAM from the liver, which contains the full-length HEPN1 on its antisense strand in the 3'-noncoding region, and assessed its expression, characteristics and functions in HCC.

METHODS

Full-length hepaCAM cDNA was isolated by rapid amplification of cDNA ends. The gene expression was examined by semi-quantitative RT-PCR in 23 paired HCC liver specimens and 5 HCC cell lines. Transfection studies, coupled with immunocytochemistry, cellular interaction analyses, colony formation and microtetrazolium assay, were employed to elucidate the localization and functions of hepaCAM.

RESULTS

The expression of hepaCAM decreased in 20/23 of HCC samples and was undetectable in 5 HCC cell lines tested. The gene product consisting of 416 amino acids displayed the typical structure of Ig-like cell adhesion molecules. The protein was glycosylated and predominantly localized on the cytoplasmic membrane. When re-expressed in HepG2, hepaCAM accelerated cell spreading (P<0.001), increased cell motility (P=0.0011), reduced colony formation (P=0.0022), and inhibited cell growth (P<0.001).

CONCLUSIONS

Gene hepaCAM, frequently silenced in HCC, encodes an Ig-like transmembrane glycoprotein and is involved in cell adhesion and growth control.

Cloning of a soluble isoform of the SgIGSF adhesion molecule that binds the extracellular domain of the membrane-bound isoform

SgIGSF (spermatogenic immunoglobulin superfamily) is a recently identified intercellular adhesion molecule of the immunoglobulin superfamily. In a mast-cell cDNA library, we found a clone that resulted from the retention of intron 7 within the mature SgIGSF message. This clone was predicted to encode a soluble isoform of SgIGSF (sSgIGSF) with 336 amino-acid residues because its open reading frame ended just before the transmembrane domain. We constructed a plasmid expressing sSgIGSF fused to the human IgG Fc fragment at its C-terminus (sSgIGSF-Fc), and transfected it into COS-7 cells. The fusion protein was readily detectable in the culture supernatant. Solid-phase binding assay showed that sSgIGSF interacted directly the extracellular domain of membrane-bound SgIGSF (mSgIGSF). We next examined whether this interaction inhibited homophilic binding of mSgIGSF by aggregation assays using L cells that did not express mSgIGSF. A stable L-cell clone that overexpressed mSgIGSF aggregated with each other but not with mock-transfected L cells, indicating that a homophilic interaction of mSgIGSF mediated the aggregation. Addition of sSgIGSF-Fc inhibited the aggregation of L cells overexpressing mSgIGSF in a dose-dependent manner. Moreover, FACScan analyses revealed the specific binding of sSgIGSF-Fc to mSgIGSF expressed in L cells. Binding of sSgIGSF-Fc to mSgIGSF appeared to inhibit homophilic interactions of mSgIGSF.

Exploiting the yeast Saccharomyces cerevisiae for the study of the organization and evolution of complex genomes

Yeast artificial chromosome (YAC) cloning systems have advanced the analysis of complex genomes considerably. They permit the cloning of larger fragments than do bacterial artificial chromosome systems, and the cloned material is more easily modified. We recently developed a novel YAC cloning system called transformation-associated recombination (TAR) cloning. Using in vivo recombination in yeast, TAR cloning selectively isolates, as circular YACs, desired chromosome segments or entire genes from complex genomes. The ability to do that without constructing a representative genomic library of random clones greatly facilitates analysis of gene function and its role in disease. In this review, we summarize how recombinational cloning techniques have advanced the study of complex genome organization, gene expression, and comparative genomics.

SgIGSF: a new mast-cell adhesion molecule used for attachment to fibroblasts and transcriptionally regulated by MITF

Microphthalmia transcription factor (MITF) is a basic-helix-loop-helix-leucine zipper-type transcription factor. The mutant mi and Mi(wh) alleles encode MITFs with deletion and alteration of a single amino acid, respectively, whereas the tg is a null mutation. In coculture with NIH/3T3 fibroblasts, the numbers of cultured mast cells (CMCs) derived from C57BL/6 (B6)(mi/mi), B6(Miwh/Miwh), and B6(tg/tg) mice that adhered to NIH/3T3 fibroblasts were one third as large as the number of B6(+/+) CMCs that adhered to NIH/3T3 fibroblasts. From a cDNA library of B6(+/+) CMCs, we subtracted messenger RNAs expressed by B6(mi/mi) CMCs and found a clone encoding SgIGSF, a recently identified member of the immunoglobulin superfamily. Northern and Western blot analyses revealed that SgIGSF was expressed in B6(+/+) CMCs but not in CMCs derived from MITF mutants. Immunocytochemical analysis showed that SgIGSF localized to the cell-to-cell contact areas between B6(+/+) CMCs and NIH/3T3 fibroblasts. Transfection of B6(mi/mi) and B6(tg/tg) CMCs with SgIGSF cDNA normalized their adhesion to NIH/3T3 fibroblasts. NIH/3T3 fibroblasts did not express SgIGSF, indicating that SgIGSF acts as a heterophilic adhesion molecule. Transfection of B6(tg/tg) CMCs with normal MITF cDNA elevated their SgIGSF expression to normal levels. These results indicated that SgIGSF mediated the adhesion of CMCs to fibroblasts and that the transcription of SgIGSF was critically regulated by MITF.

Pharmacogenetics of anticancer drug sensitivity in non-small cell lung cancer

In mammalian cells, the process of malignant transformation is characterized by the loss or down-regulation of tumor-suppressor genes and/or the mutation or overexpression of proto-oncogenes, whose products promote dysregulated proliferation of cells and extend their life span. Deregulation in intracellular transduction pathways generates mitogenic signals that promote abnormal cell growth and the acquisition of an undifferentiated phenotype. Genetic abnormalities in cancer have been widely studied to identify those factors predictive of tumor progression, survival, and response to chemotherapeutic agents. Pharmacogenetics has been founded as a science to examine the genetic basis of interindividual variation in drug metabolism, drug targets, and transporters, which result in differences in the efficacy and safety of many therapeutic agents. The traditional pharmacogenetic approach relies on studying sequence variations in candidate genes suspected of affecting drug response. However, these studies have yielded contradictory results because of the small number of molecular determinants of drug response examined, and in several cases this approach was revealed to be reductionistic. This limitation is now being overcome by the use of novel techniques, i.e., high-density DNA and protein arrays, which allow genome- and proteome-wide tumor profiling. Pharmacogenomics represents the natural evolution of pharmacogenetics since it addresses, on a genome-wide basis, the effect of the sum of genetic variants on drug responses of individuals. Development of pharmacogenomics as a new field has accelerated the progress in drug discovery by the identification of novel therapeutic targets by expression profiling at the genomic or proteomic levels. In addition to this, pharmacogenetics and pharmacogenomics provide an important opportunity to select patients who may benefit from the administration of specific agents that best match the genetic profile of the disease, thus allowing maximum activity.

Identification of the Tslc1 gene, a mouse orthologue of the human tumor suppressor TSLC1 gene

We have recently identified the TSLC1 gene as a novel tumor suppressor in human non-small lung cancer on chromosome 11q23.2. TSLC1 encodes a membrane glycoprotein showing significant homology with immunoglobulin superfamily molecules. Here, we report the isolation of a mouse orthologous gene, Tslc1. The Tslc1 cDNA contains a single open reading frame of 1335 bp encoding a putative protein of 445 amino acids, and its expression was detected in all tissues examined. The Tslc1 gene is mapped on mouse chromosome 9, a synteny of human chromosome 11q, and is composed of ten exons, the exon-intron junctions being highly conserved between human and mouse. The predicted amino acids of mouse Tslc1 display 98% identity with that of human TSLC1. Furthermore, data base analysis indicates that the amino acid sequences corresponding to the cytoplasmic domain of Tslc1 are identical in five mammals and highly conserved in vertebrates, suggesting an important role of Tslc1 in normal cell-cell interaction.