title: Cyclin D1 is necessary but not sufficient for anchorage-independent growth of rat mammary tumor cells and is associated with resistance of the Copenhagen rat to mammary carcinogenesis.
abstract: To identify genes associated with the resistance of Copenhagen (Cop) rats to mammary carcinogenesis, we infused a retrovirus harboring v-Ha-ras directly into the main mammary ducts of resistant F1 rats from a cross between Cop and susceptible Wistar Furth (WF) rats. Adenocarcinomas formed in approximately 50% of infused glands. Cell lines derived from these tumors were clonal, but did not share a common viral integration site, suggesting that a high level of v-Ha-ras expression was able to overcome resistance in the F1 rats. Some of the cell lines were able to grow in soft agar, but a significant number did not display anchorage-independent growth. These growth characteristics were independent of v-Ha-ras expression levels. The ability to grow in soft agar was associated with the size of tumors induced by injecting the cells into nude mice, and showed a striking positive association with the expression of cyclin D1. Furthermore, while resistance to anchorage-independent growth was fully overcome by transfection of cyclin D1 in some clones, in the others the effect was partial. A similar pattern of cyclin D1 upregulation and growth in soft agar was also observed when the cells were transfected with an active form of beta-catenin. Hybrid cells from the somatic fusion of an anchorage-dependent to an anchorage-independent clone did not grow in soft agar. These results suggest that while a high expression level of cyclin D1 is necessary for anchorage-independent growth in all clones, it is not sufficient for full growth capacity in soft agar, raising the possibility that the loss of a tumor suppressor gene in the cell lines is required to fully confer anchorage-independent growth. Our anchorage-dependent and -independent rat mammary tumor-derived cell lines may recapitulate the resistance and susceptibility of Cop and WF rats, respectively, to mammary carcinogenesis that could facilitate the identification of breast cancer susceptibility genes.
authors.affiliation: Molecular and Cell Biology Research, Sunnybrook and Women's College Health Sciences Centre, Toronto, ON, Canada.
authors.forename: You-Jun
authors.initials: YJ
authors.lastname: Li
authors.forename: Runlan
authors.initials: R
authors.lastname: Song
authors.forename: James E
authors.initials: JE
authors.lastname: Korkola
authors.forename: Michael C
authors.initials: MC
authors.lastname: Archer
authors.forename: Yaacov
authors.initials: Y
authors.lastname: Ben-David
mesh_terms: D000818:Animals; D002459:Cell Fusion; D002471:Cell Transformation, Neoplastic / Q000378:metabolism*; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism*; D005260:Female; D011905:Genes, ras; D008325:Mammary Neoplasms, Experimental / Q000209:etiology / Q000378:metabolism* / Q000821:virology; D051381:Rats; D012190:Retroviridae / Q000235:genetics / Q000378:metabolism
chemical_list: D019938:Cyclin D1