| Carcinogenesis is a multi-step process involving the activation of oncogenes and/or the inactivation of tumor suppressor genes. For ovarian cancer, one of the complex structural aberrations observed involves amplified DNA sequences which appear as homogeneous staining regions (hsr) on marker chromosomes. To identify the origin of an hsr, chromosome microdissection, polymerase chain reaction and fluorescence in situ hybridization (FISH) was applied to the two ovarian cancer cell lines MLS/P and GR. FISH studies with an hsr probe derived from these markers identified the oncogene c- myc as the primary component of the hsr in both cell lines.;Loss of heterozygosity of chromosome 11 has been frequently identified in human ovarian carcinoma, suggesting that chromosome 11 may carry a relevant tumor suppressor gene(s). To study the pathogenic role of chromosome 11 in ovarian carcinogenesis, microcell-mediated chromosome transfer was applied to introduce chromosome 11 into the ovarian carcinoma cell line SKOV-3. A panel of five hybrid clones was generated. In vivo tumorigenicity studies showed two clones to be completely non-tumorigenic and two to be slow-growing tumorigenic. To identify differentially expressed transcripts, cDNA subtraction and microarray screening was performed. Using these methods, a cDNA transcript corresponding to the Thy-1 gene located at chromosome 11q23-24 was found to be exclusively expressed in the two non-tumorigenic cell clones. Additionally, several cell growth and differentiation related genes; Thrombospondin-1, SPARC, and Fibronectin were expressed in both slow-growing and non-tumorigenic clones. Transfection of Thy-1 cDNA into SKOV-3 reduced tumor growth but did not suppress it completely. However, abolishing Thy-1 expression from clone 11(C)9-8 by antisense transfection resulted in restoration of tumorigenicity. To study the downstream effects of Thy-1, an inducible expression system was established which revealed Thrombospondin-1 and Fibronectin up-regulation upon Thy-1 induction. In summary, these results indicate that Thy-1 expression alone cannot suppress tumorigenicity. However, abrogation of Thy-1 expression from non-tumorigenic cells can induce tumorigenesis. Furthermore, the tumor suppressing function of Thy-1 may involve Fibronectin and Thrombospondin-1 which affect cell differentiation and angiogenesis inhibition, respectively. Therefore, Thy-1 is a putative tumor suppressor gene for ovarian cancer. |
