RNA interference-based functional dissection of the 17q12 amplicon in breast cancer reveals contribution of coamplified genes
ABSTRACT DNA amplification is a frequent occurrence in cancer genomes. While tumor amplicons may harbor known oncogenes "driving" amplification, amplicons rarely comprise only single genes. The potential functional contribution of coamplified genes remains largely unexplored. In breast cancer, 20-30% of tumors exhibit amplification within chromosome band 17q12, containing the ERBB2 oncogene. Analysis of array-based comparative genomic hybridization and expression profiling data indicate that the minimum region of recurrent amplification (i.e., the amplicon "core") at 17q12 includes two other genes, GRB7 and STARD3, which exhibit elevated expression when amplified. Western blot analysis confirms overexpression of each at the protein level in breast cancer cell lines SKBR3 and BT474 harboring amplification. In these cell lines (but not in control MCF7 breast cancer cells lacking 17q12 amplification), targeted knockdown of ERBB2 expression using RNA interference (RNAi) methods results in decreased cell proliferation, decreased cell-cycle progression, and increased apoptosis. Notably, targeted knockdown of either GRB7 or STARD3 also leads to decreased cell proliferation and cell-cycle progression, albeit to a lesser extent compared with ERBB2 knockdown. We conclude that the amplification and resultant overexpression of genes coamplified with ERBB2 at 17q12 can contribute to proliferation levels of breast cancer cells. Our findings validate the utility of RNAi in the functional interrogation of tumor amplicons, and provide evidence for a contribution of coamplified genes to tumor phenotypes.
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ABSTRACT: C35 is a 12 kDa membrane-anchored protein endogenously over-expressed in many invasive breast cancers. C35 (C17orf37) is located on the HER2 amplicon, between HER2 and GRB7. The function of over-expressed C35 in invasive breast cancer is unknown. Tissue microarrays containing 122 primary human breast cancer specimens were used to examine the association of C35 with HER2 expression. Cell lines over-expressing C35 were generated and tested for evidence of cell transformation in vitro. In primary breast cancers high levels of C35 mRNA expression were associated with HER2 gene amplification. High levels of C35 protein expression were associated with hallmarks of transformation, such as, colony growth in soft agar, invasion into collagen matrix and formation of large acinar structures in three-dimensional (3D) cell cultures. The transformed phenotype was also associated with characteristics of epithelial to mesenchymal transition, such as adoption of spindle cell morphology and down-regulation of epithelial markers, such as E-cadherin and keratin-8. Furthermore, C35-induced transformation in 3D cell cultures was dependent on Syk kinase, a downstream mediator of signalling from the immunoreceptor tyrosine-based activation motif, which is present in C35. C35 functions as an oncogene in breast cancer cell lines. Drug targeting of C35 or Syk kinase might be helpful in treating a subset of patients with HER2-amplified breast cancers.British Journal of Cancer 07/2010; 103(3):401-10. DOI:10.1038/sj.bjc.6605763 · 4.82 Impact Factor
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ABSTRACT: To knockdown the C-erbB2 gene in salivary gland adenoid cystic carcinoma SACC-83 cells using RNA interference, and determine the effect of silencing C-erbB2 on cell proliferation. C-erbB2-siRNA was transfected into SACC-83 cells. RT-PCR and immunohistochemistry were used to detect C-erbB2 expression in SACC-83 cells. Cell proliferation was measured by the MTT assay and gene knockdown was achieved by RNA interference. Apoptosis was analyzed by flow cytometry. Compared with the control, C-erbB2 mRNA expression was decreased in the C-erbB2-siRNA transfection group, and immunohistochemical analysis indicated that C-erbB2 protein expression was decreased. After C-erbB2-siRNA was transfected for 48 h, absorbance at 570 nm (MTT) was 0.185±0.021 compared with 0.354±0.034, 0.299±0.053, and 0.314±0.049 in the blank control, liposome control and negative control siRNA groups, respectively. The differences were statistically significant (P < 0.05) between the C-erbB2-siRNA group and the control groups. Following the C-erbB2 knockdown, the percentage of apoptotic cells was 5.63% compared with 2.04%, 2.85%, and 2.98% in the three control groups, respectively. Proliferation of SACC-83 cells was inhibited, and early apoptotic cells were increased. RNA interference can effectively silence C-erbB2 gene expression and inhibit growth of SACC-83 cells, which indicates the potential of targeting this gene as a novel gene therapy approach for the treatment of salivary gland adenoid cystic carcinoma.05/2010; 24(3):215-22. DOI:10.1016/S1674-8301(10)60031-0
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ABSTRACT: Breast cancer is a heterogeneous disease, appreciable by molecular markers, gene-expression profiles, and most recently, patterns of genomic alteration. In particular, genomic profiling has revealed three distinct patterns of DNA copy-number alteration: a "simple" type with few gains or losses of whole chromosome arms, an "amplifier" type with focal high-level DNA amplifications, and a "complex" type marked by numerous low-amplitude changes and copy-number transitions. The three patterns are associated with distinct gene-expression subtypes, and preferentially target different loci in the genome (implicating distinct cancer genes). Moreover, the different patterns of alteration imply distinct underlying mechanisms of genomic instability. The amplifier pattern may arise from transient telomere dysfunction, although new data suggest ongoing "amplifier" instability. The complex pattern shows similarity to breast cancers with germline BRCA1 mutation, which also exhibit "basal-like" expression profiles and complex-pattern genomes, implicating a possible defect in BRCA1-associated repair of DNA double-strand breaks. As such, targeting presumptive DNA repair defects represents a promising area of clinical investigation. Future studies should clarify the pathogenesis of breast cancers with amplifier and complex-pattern genomes, and will likely identify new therapeutic opportunities.Molecular oncology 04/2010; 4(3):255-66. DOI:10.1016/j.molonc.2010.04.001 · 5.94 Impact Factor