199731

CADM4

IGSF4C|NECL4|Necl-4|TSLL2|synCAM4;cell adhesion molecule 4;CADM4;cell adhesion molecule 4

TSLC1-like 2|TSLC1-like protein 2|immunoglobulin superfamily member 4C|immunoglobulin superfamily, member 4C|nectin-like 4|nectin-like protein 4

19q13.31

protein-coding

We have recently identified the TSLC1 gene as a novel tumor suppressor in human non-small cell lung cancers. TSLC1 encodes a membrane glycoprotein with an extracellular domain homologous to those of immunoglobulin superfamily proteins. Truncation of TSLC1 in the cytoplasmic domain in a primary human tumor suggests that this domain is important for tumor suppressor activity. Here, we report the isolation of two TSLC1-like genes, TSLL1 and TSLL2, based on their structural homology with the sequences corresponding to the cytoplasmic domain of TSLC1. Significant similarity was also observed in the extracellular domain as well as in the overall gene structure, indicating that these three genes form a unique subfamily (the TSLC1-gene family) in the immunoglobulin superfamily genes. In contrast to the ubiquitous expression of TSLC1, TSLL1 is expressed exclusively in adult and fetal human brain, while TSLL2 is expressed in several specific tissues including prostate, brain, kidney and some other organs. expression of TSLL1 and TSLL2 was lost or markedly reduced in many human glioma cell lines or some prostate cancer cell lines, suggesting that loss of expression of these genes might be involved in some human cancers.

The TSLL2/IGSF4C encodes an immunoglobulin (Ig) superfamily molecule showing significant homology with a lung tumor suppressor, TSLC1. The TSLL2 protein of 55 kDa is mainly expressed in the kidney, bladder, and prostate in addition to the brain. Here, we report the biological significance of TSLL2 in the urinary tissues. An immunohistochemical study reveals that TSLL2 is expressed at the cell-cell attachment sites in the renal tubules, the transitional epithelia of the bladder, and the glandular epithelia of the prostate. Confocal microscopy analysis demonstrates that TSLL2 is localized in the lateral membranes in polarized Mardin-Darby canine kidney (MDCK) cells. TSLL2 forms homo-dimers and its overexpression induces aggregation of suspended MDCK cells in a Ca2+/Mg2+-independent manner, suggesting that it is involved in cell adhesion through homophilic trans-interaction. The TSLL2 gene is mapped on the chromosomal region 19q13.2, whose loss of heterozygosity has been frequently reported in prostate cancer. TSLL2 protein is lost in nine of nine primary prostate cancers and in a prostate cancer cell, PPC-1. Introduction of TSLL2 into PPC-1 strongly suppresses subcutaneous tumor formation in nude mice. These results suggest that TSLL2 is a new member of the Ig superfamily cell adhesion molecules and is a tumor-suppressor candidate in prostate cancer.

Nectin-like molecule 4 (Necl-4)/CADM4, a transmembrane cell-cell adhesion molecule with three Ig-like domains, was shown to serve as a tumor suppressor, but its mode of action has not been elucidated. In this study, we showed that Necl-4 interacted in cis with ErbB3 through their extracellular regions, recruited PTPN13 and inhibited the heregulin-induced activation of the ErbB2/ErbB3 signaling. In addition, we extended our previous finding that Necl-4 interacts in cis with integrin alpha6 beta4 through their extracellular regions and found that Necl-4 inhibited the phorbol ester-induced disassembly of hemidesmosomes. These results indicate that Necl-4 serves as a tumor suppressor by inhibiting the ErbB2/ErbB3 signaling and hemidesmosome disassembly.