CHFR Expression in Breast Cancer Cells:Its Relevance to Tumorigenesis and Genomic Stability.

[摘要] Breast cancer can develop when genes that control the cell cycle and genomic stability are aberrantly expressed or non-functional.CHFR encodes an E3 ubiquitin ligase that reportedly delays mitosis in response to microtubule-targeting drugs (i.e. nocodazole and taxanes).Loss of CHFR mRNA expression has been reported in many cancers, including breast cancer, but the relevance of this to tumorigenesis remains unknown.To test if CHFR was relevant for mammary tumorigenesis, we analyzed the effects of altered expression in breast cancers.Nearly 40% of cultured and primary breast cancers had low or no CHFR, which was associated with large tumor size in patient samples.Decreased CHFR expression by RNAi in immortalized human mammary epithelial cell (IHMEC) lines resulted in taxane sensitivity and the acquisition of tumorigenic phenotypes including faster growth rates, higher mitotic indices, enhanced invasiveness and motility, epithelial-to-mesenchymal transitions, increased aneuploidy, and colony formation in soft agar.Conversely, over-expressing CHFR in breast cancer cells caused slower growth and decreased invasiveness and motility.To determine if CHFR was critical for genomic stability, cells transfected with CHFR siRNA were analyzed for chromosome segregation defects.Transient CHFR loss led to increased aneuploidy, misaligned metaphase chromosomes, anaphase bridges, multi-polar condensed spindles, multi-nucleated cells, and mislocalization of the mitotic checkpoint proteins MAD2 and BUBR1.CHFR was found to interact with three proteins required for mitotic spindle formation and chromosome segregation, including MAD2 and Aurora A where CHFR loss led to elevated Aurora A oncoprotein levels, but no change in MAD2 expression.Alpha-tubulin was identified as a novel target for CHFR-mediated ubiquitination and degradation after treatment with nocodazole.Decreased CHFR increased acetylated alpha-tubulin, a mitotic spindle protein implicated in cellular response to taxane treatment.These findings indicate that CHFR has tumor suppressive qualities and may be a biomarker for chemotherapeutic response to taxanes.CHFR has a previously unrecognized role as a regulator of genomic stability via its functional impact on BUBR1, MAD2, Aurora A, and alpha-tubulin.CHFR may be one of the few proteins that can control the cell cycle, chemotherapeutic response, and genomic stability - processes that go awry in breast cancer.

[发布机构] University of Michigan

[效力级别] Tumor Suppressor

[关键词] Mitototic Checkpoints;Tumor Suppressor;Genomic Instability;Genetics;Molecular;Cellular and Developmental Biology;Health Sciences;Human Genetics