Cellular and Molecular Biology


Relationship between B-Cell-specific moloney murine leukemia virus integration site 1 (BMI-1) and homologous recombination regulatory genes in invasive ductal breast carcinomas

Giórgia Gobbi da Silveira1, João Paulo Oliveira-Costa1,2, Danilo Figueiredo Soave1, Juliana Silva Zanetti1, Fernando Augusto Soares2 and Alfredo Ribeiro-Silva1

1Department of Pathology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, São Paulo, Brazil and 2Department of Pathologic Anatomy, A. C. Camargo Cancer Hospital, São Paulo, Brazil

Offprint requests to: Alfredo Ribeiro-Silva, Department of Pathology, Ribeirão Preto Medical School, University of São Paulo, Avenida Bandeirantes 3900, 14049-900, Ribeirão Preto, São Paulo, Brazil. e-mail: arsilva@fmrp.usp.br

Summary. B-cell-specific Moloney murine leukemia virus integration site 1 (Bmi-1) is a Polycomb group protein that is able to induce telomerase activity, enabling the immortalization of epithelial cells. Immortalized cells are more susceptible to double-strand breaks (DSB), which are subsequently repaired by homologous recombination (HR). BRCA1 is among the HR regulatory genes involved in the response to DNA damage associated with the RAD51 protein, which accumulates in DNA damage foci after signaling H2AX, another important marker of DNA damage. Topoisomerase IIIß (topoIIIß) removes HR intermediates before chromosomal segregation, preventing damage to cellular DNA structure. In breast carcinomas positive for BMI-1 the role of proteins involved in HR remains to be investigated. The aim of this study was to evaluate the association between BMI-1 and homologous recombination proteins. Using tissue microarrays containing 239 cases of primary breast tumors, the expression of Bmi-1, BRCA-1, H2AX, Rad51, p53, Ki-67, topoIIIß, estrogen receptors (ER), progesterone receptors (PR), and HER-2 was analyzed by immunohistochemistry. We observed high Bmi-1 expression in 66 cases (27.6%). Immunohistochemical overexpression of BMI-1 was related to ER (p=0.004), PR (p<0.001), Ki-67 (p<0.001), p53 (p=0.003), BRCA-1 (p= 0.003), H2AX (p=0.024) and topoIIIß (p<0,001). Our results show a relationship between the expression of BMI-1 and HR regulatory genes, suggesting that Bmi-1 overexpression might be an important event in HR regulation. However, further studies are necessary to understand the mechanisms in which Bmi-1 could regulate HR pathways in invasive ductal breast carcinomas. HIstol Histopathol 27, 1353-1359 (2012)

Key words: BMI-1, Homologous recombination, Invasive ductal carcinoma, Breast cancer