BRCA1 Protein and Nucleolin Colocalize in Breast Carcinoma Tissue and Cancer Cell Lines

Abstract

The breast and ovarian cancer susceptibility gene BRCA1 encodes a tumor suppressor. BRCA1 protein, which is involved in DNA damage response , has been thought to be found primarily in cell nuclei. In the present investigation , immunohistological studies of BRCA1 protein in frozen breast cancer tissue and MCF7 and HeLa cell lines revealed BRCA1 expression in both nucleoli and nucleoplasmic foci. The majority of known cancer-causing BRCA1 mutations induce protein truncation, highlighting a requirement for the BRCA1 C-terminal domain repeats in mediating BRCA1 tumor suppressor function. However, somatic mutations in BRCA1 have not been found in sporadic breast cancer tumor tissue. 5 Instead it is thought that BRCA1 participates in the tumorigenesis of sporadic breast cancer through reduction in BRCA1 mRNA and protein levels, as compared with normal tissue. -10Functionally, BRCA1 participates in many signaling pathways involved in transcription and checkpoint control, and is recruited for the formation of DNA repair complexes, in association with proteins such as Mre11-Nbs1-Rad50, and BRCA2.11 Cell cycle studies have shown that BRCA1 protein is found in nuclear foci (dots) during S-phase, and after ␥-irradiation BRCA1 colocalizes with BRCA1-associated ring domain and Rad51-containing foci. 12Our immunohistological studies of frozen tissue sections from breast carcinomas and transmission electron microscopic studies of estrogen-stimulated MCF7 cells have shown nuclear, nucleolar, and cytoplasmic BRCA1 protein staining. 13,14 With transmission electron microscopy, we found the BRCA1 nuclear staining on the periphery of dots, around nucleoli, and also in the cytoplasm in

Genome Wide Proteomics of ERBB2 and EGFR and Other Oncogenic Pathways in Inflammatory Breast Cancer

“…For the c-MYC pathway (Table 5) the higher ratios of EGFR transcript were associated with increased proteomic levels of branched chain amino-acid transaminase 1 (BCAT1), cytosolic, carbamoyl-phosphate synthetase 2 (CAD) and nucleolin (NCL), while higher ERBB2 ratios are associated with transferrin receptor (TFRC) and metadherin (MTDH). Examples of the significance of these proteins include the observation that nucleolin colocalizes with BRCA1 in breast carcinoma tissue 47 , and metahedrin is a valuable marker of breast cancer progression and high expression may play a role in tumorigenesis of breast cancer 48–49 . As was observed for the EGFR pathway, most of the proteins in Table 4 (GRB2) and Table 5 (MYC) contained a significant number of interactors (12/17 and 28/31) and literature associations with cancer (16/17 and 24/31) respectively.…”

S100A14, a Member of the EF-hand Calcium-binding Proteins, Is Overexpressed in Breast Cancer and Acts as a Modulator of HER2 Signaling

“…Immunofluorescence-Cells were grown at low density on sterilized coverslips for 24 h. Cell sections were washed with PBS buffer three times and fixed in 4% paraformaldehyde for 15 min and processed for the immunofluorescence procedure as described previously (15). Primary antibodies used were rabbit anti-S100A14 (1:50) (gift from Dr. Iver Petersen) and mouse anti-HER2 (1:100) (sc-08, Santa Cruz Biotechnology, Inc., Dallas, TX).…”

Localization of BRCA1 protein in breast cancer tissue and cell lines with mutations

“…Our previous studies have shown that BRCA1 protein is localized in tumor cell nuclei and nucleoli in frozen tissue sections, and is co-localized with nucleolin in MCF7 and HeLa cells [26,27]. Chambon et al [28] have shown in light and electron microscopic studies of estradiol-treated MCF7 cells that BRCA1 nuclear staining was found in dots around nucleoli, and in the cytoplasm in multivesicular bodies near the Golgi.…”