7070

THY1

CD90;Thy-1 cell surface antigen;THY1;Thy-1 cell surface antigen

CDw90|Thy-1 T-cell antigen|thy-1 antigen|thy-1 membrane glycoprotein

11q23.3

protein-coding

Microcell-mediated transfer of chromosome 11 into the human ovarian cancer cell line SKOV-3 results in suppression of tumorigenicity in severe combined immunodeficiency (SCID) mice. To identify the differentially expressed transcripts associated with suppression of tumorigenicity, cDNA populations from the slow-growing tumorigenic clone 11(H)8-3, tumorigenic clone 11(H)8-4, and parental SKOV-3 cells were subtracted from the nontumorigenic clones, 11(H)7-2 and 11(C)9-8. The subtracted cDNA populations were either cloned, sequenced and searched in GenBank, or analyzed by gene discovery array screening. A cDNA transcript corresponding to the THY1 gene located at chromosome 11q23 approximately q24 was found to be exclusively expressed in the two nontumorigenic cell clones. In contrast, THY1 expression was not detected in SKOV-3, the tumorigenic hybrid clones, or six other tumorigenic ovarian cancer cell lines. Further analysis using immunocytochemistry and quantitative flow cytometry with a Thy-1-specific antibody confirmed the exclusive expression of THY1 at the protein level in the two nontumorigenic clones. Several cell growth and differentiation-related genes, including thrombospondin 1 (THBS1), SPARC [secreted protein, acidic, cysteine-rich (osteonectin)], and fibronectin (FN1) were also found to be upregulated in the nontumorigenic clones; however, these were expressed in the slow-growing tumorigenic clones as well. expression of these genes was not observed in the parental SKOV-3 cell line and therefore must be regulated by a gene or genes on chromosome 11. Our results suggest that THY1 is a putative tumor suppressor gene for ovarian cancer and that THBS1, SPARC, and FN1 are genes associated with the regulation of in vivo tumor growth rate.

In our recent studies, the expression of the THY1 gene encoding a 25-28 kDa glycoprotein located at 11q23-q24, was found to be associated with complete tumor suppression of the ovarian cancer cell line SKOV-3 after the transfer of chromosome 11. These studies raised the possibility that THY1 maybe a candidate tumor suppressor gene for ovarian cancer. To investigate this, the complete cDNA sequence for THY1 was cloned and transfected into SKOV-3 ovarian cancer cells. The expression of THY1 in the transfectants was confirmed by Northern blot analysis, immunocytochemistry, and flow cytometry. Both SKOV-3-THY1 and SKOV-3-null cells were inoculated subcutaneously into severe combined immunodeficiency (SCID) mice to determine in vivo tumorigenicity. THY1 transfectants formed tumors, but overall tumor growth rate and tumor size was significantly reduced compared with their null counterparts. To further correlate THY1 expression with tumorigenicity, the THY1 antisense was transfected into the nontumorigenic clone, 11(C)9-8, which resulted in restoration of tumorigenicity. These data indicate that THY1 expression alone cannot suppress tumorigenicity; however, abrogation of THY1 expression from nontumorigenic cells can restore tumorigenesis. Taken together, the data suggest that THY1 is necessary but not sufficient to suppress ovarian tumorigenicity. Therefore, THY1 can be designated as a putative tumor suppressor gene for human ovarian cancer.

THY1 was previously identified as a candidate tumor suppressor gene (TSG) associated with lymph node metastases in nasopharyngeal carcinoma (NPC) through functional studies. It was identified by oligonucleotide microarray analysis as an interesting differentially expressed gene. However, direct functional evidence is still lacking for THY1 being a TSG in NPC, as in vivo tumorigenicity assays have not been previously reported in our last study of THY1. In this study, a tetracycline-inducible expression vector, pETE-Bsd, was used to obtain stable transfectants of THY1. The stringent in vivo tumorigenicity assay results show that the activation of THY1 suppresses tumor formation of HONE1 cells in nude mice, and the tumor formation ability was restored in the presence of doxycycline (a tetracycline analog), when the gene is shut off. Functional inactivation of this gene is observed in all the tumors derived from the tumorigenic transfectant. The tumor suppressive effect could be repressed by knockdown of THY1 expression in nontumorigenic microcell hybrids. Further studies indicate that expression of THY1 inhibits HONE1 cell growth in vitro by arresting cells in G(0)/G(1) phase. It greatly reduces the ability for anchorage-independent growth. The invasiveness of HONE1 cells was also inhibited by the expression of THY1. These findings suggest that THY1 is a TSG in NPC, which is involved in invasion and shows an association with tumor metastasis. Taken together, THY1 clearly plays an important functional role in tumor suppression in NPC.