Abstract
A spontaneously immortalized clonal granulosa cell line (SIGC) derived from primary rat ovarian granulosa cell cultures was developed as a model system to explore the process of transformation using an epithelial cell type. SIGC has an epithelial morphology and grows in culture without undergoing luteinization. The cell line is thought to represent an intermediate step in carcinogenesis because it seems to grow indefinitely in culture but does not form clones in soft agar or tumors in nude mice. Indirect immunofluorescence and Western blot analysis verified the constitutive expression of the recessive oncogene product p53 in the cell line, thereby suggesting a possible mechanism of immortalization. Ultrastructural studies indicated that SIGC cells are characterized by an undifferentiated phenotype with prominent intermediate filaments, desmosomes, and gap junctions. The identification of cytokeratin by indirect immunofluorescence and Western blot analysis suggests that SIGC functions as an epithelial cell type. Functional studies of cell-cell communication by a dye transfer technique (fluorescence recovery after photobleaching) showed reduced communication compared to normal primary granulosa cells in culture. SIGC cells were transfected with early region genes of SV40 virus in an attempt to generate fully transformed cell lines. The resulting cell line SV-SIGC expressed T-antigen, was anchorage independent, formed tumors in nude mice, and had reduced intercellular communication as compared to SIGC cells. Explants from the tumors in nude mice were used to generate another cell line (T-SV-SIGC), which exhibited further reduction in both the incidence and the rate of communication. These results clearly demonstrated a progressive loss of functional communication during multistep transformation of an ovarian cell type. These data demonstrate that this assay system based on an epithelioid cell type can be used to study the relationship between intercellular communication and the multistep process of carcinogenesis.
Footnotes
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↵1 This work was supported in part by Basic Research Grant 1-1052 from the March of Dimes Birth Defects Foundation, a Texas A&M University College of Veterinary Medicine Enhancement Project, and a grant from the Texas Agricultural Experiment Station to R. C. B.
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↵2 These studies comprise a portion of an investigation submitted in partial fulfillment for the Doctor of Philosophy degree in the Department of Veterinary Anatomy, Texas A&M University.
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↵3 To whom requests for reprints should be addressed.
- Received March 12, 1990.
- Accepted October 26, 1990.
- ©1991 American Association for Cancer Research.
Volume 51, Issue 2
