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BRCA1 partially reverses the transforming activity of the ras oncogene
A Kumar1, C Knott, K Kuus-Reichel
1Hybritech Incorporated, a subsidiary of Beckman Coulter Inc., San Diego, CA 92196-9006, USA. akumar@beckman.com
Abstract:
The BRCA1 gene is associated with hereditary breast and ovarian cancers. BRCA1 fits the model of a classic tumor suppressor gene, a hypothesis supported by recent work demonstrating that expression of BRCA1 inhibits growth of breast and ovarian cancer cell lines. The present study was designed to test the potential of BRCA1 to reverse the transforming activity of the ras oncogene. The v-Ha ras oncogene was cloned downstream of the retrovirus LTR and stably expressed in Rat-1 cells (Rat-1/ras). Rat-1/ras (R/R) cells were fully transformed as indicated by change in morphology, colony formation in soft-agarose and tumor induction in nude mice. BRCA1 was stably expressed in R/R cells under the CMV promoter (R/R-BRCA1). The expression of ras and BRCA1 was confirmed by Western blot using monoclonal antibodies (mAbs) specific to ras and BRCA1, respectively. R/R-BRCA1 cells grew slower than the negative control, which was R/R cells transfected with vector alone (R/R-pCEP4). R/R-BRCA1 cells generated approximately 5 to 10 times less colonies in a soft-agarose assay compared to the negative control. When injected into nude mice, R/R-BRCA1 cells exhibited a delayed onset of tumorigenesis and generated smaller tumors compared to R/R or R/R-pCEP4 cells. These data strongly suggest that BRCA1 partially reverses the transforming activity of the v-Ha ras oncogene indicating that BRCA1 can bypass the effects of the v-Ha ras oncogene on cell growth. BRCA1, therefore, may be used in therapy of tumors arising due to activation of v-Ha ras oncogene.
Insights
The BRCA1 gene partially reverses the transforming activity of the ras oncogene, inhibiting cancer cell growth and tumor formation. This suggests BRCA1 as a potential therapy for ras-activated tumors.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- Hereditary breast and ovarian cancers are linked to the BRCA1 gene.
- BRCA1 functions as a tumor suppressor, inhibiting cancer cell line growth.
- The ras oncogene promotes cell transformation and tumor development.
Purpose of the Study:
- To investigate BRCA1's potential to reverse the transforming activity of the v-Ha ras oncogene.
- To assess BRCA1's effect on ras-induced cellular transformation and tumorigenesis.
Main Methods:
- Stably expressed v-Ha ras oncogene in Rat-1 cells (Rat-1/ras).
- Introduced BRCA1 into ras-transformed cells (R/R-BRCA1).
- Confirmed gene expression via Western blot; assessed cell growth, soft-agarose colony formation, and tumor induction in nude mice.
Main Results:
- R/R-BRCA1 cells exhibited slower growth compared to controls.
- BRCA1 expression reduced soft-agarose colony formation by 5-10 fold.
- Tumorigenesis onset was delayed, and tumors were smaller in R/R-BRCA1 injected mice.
Conclusions:
- BRCA1 partially reverses the transforming effects of the v-Ha ras oncogene.
- BRCA1 can counteract ras oncogene-driven cell growth.
- BRCA1 shows therapeutic potential for tumors with activated v-Ha ras.