Down-regulation of the Tumor Suppressor Protein 14-3-3σ Is a Sporadic Event in Cancer of the Breast

Abstract

14-3-3 proteins comprise a family of highly conserved and broadly expressed multifunctional regulatory proteins that are involved in various cellular processes such as cell cycle progression, cell growth, differentiation, and apoptosis. Transcriptional expression of the isoform of 14-3-3 is frequently impaired in human cancers, including carcinomas of the breast, which has led to the suggestion that this protein might be involved in the neoplastic transformation of breast epithelial cells. Here we report on the analysis of 14-3-3 expression in primary breast tumors using a proteomic approach complemented by immunohistochemical analysis by means of specific antibodies against this isoform. We show that the levels of expression of 14-3-3 were similar in non-malignant breast epithelial tissue and matched malignant tissue with only sporadic loss of expression observed in 3 of the 68 tumors examined. Moreover we show that 14-3-3 immunoreactivity was restricted to epithelial cells and significantly stronger in the myoepithelial cells that line the mammary ducts and lobules. The lack of expression of 14-3-3 in the three breast carcinomas was not associated with high levels of expression of the dominant-negative transcriptional regulator ⌬Np63 or with increased expression of estrogen-responsive finger protein, a ubiquitin-protein ligase (E3) that targets 14-3-3 for proteolysis. Validation of the results was performed retrospectively on an independent clinical tumor sample set using a tissue microarray containing 65 primary tumors. Our data suggest that, contrary to what was previously thought, loss of expression of 14-3-3 protein is not a frequent event in breast tumorigenesis. Molecular & Cellular Proteomics 4: 555-569, 2005.

14-3-3σ stabilizes a complex of soluble actin and intermediate filament to enable breast tumor invasion

“…Additionally, 14-3-3σ functions as an enforcer of the G 2 /M checkpoint in HCT116 colorectal cancer cells by sequestering cyclin B1 and cdc2 from the nucleus (19,20) and facilitates mitotic translation in HeLa and U2OS cells (21). Despite the high frequency of promoter methylation, immunohistochemical analysis, nevertheless, demonstrated that 14-3-3σ silencing at the protein level does not occur as frequently as initially proposed (22), and in a pilot study, 14-3-3σ was found to be expressed highly in 10 of 12 cases of BLBCs (23). We, thus, hypothesized that 14-3-3σ may be a useful marker for progression of basal-like breast cancers and may functionally contribute to the aggressive clinical features of this subtype.…”

Sustained induction of epithelial to mesenchymal transition activates DNA methylation of genes silenced in basal-like breast cancers

“…These data suggest that TGF␤ is sufficient to induce the phenotypic alterations observed in a serum-rich environment, but that additional factors (or time) are required for the epigenetic modifications that render EMT heritable to occur. To rule out the unlikely possibility that the mesenchymal features in these cells were due to the selection and expansion of a rare contaminating population of fibroblasts, we analyzed the promoter gene region for the protein 14-3-3 , which is a mammary epithelial-specific marker that is methylated in fibroblasts but unmethylated in epithelial cells (20). This locus remained unmethylated in all our cells, including those that acquired a mesenchymal morphology, confirming their epithelial origin (Fig.…”

Proteomic studies in breast cancer (Review)

“…In addition, breast cancers differentiate according to their mutation conveyance in the BRCA1 and BRCA2 genes. This genotypic classification has been confirmed using DNA microarray with a series of genes also containing the cyclin D1 (CCND1) gene (31). Palacios et al (20) confirmed this molecular classification using a protein level study with 37 protein biomarkers.…”

“…These proteins are involved in the regulation of the cell cycle machinery at several key points. Additionally, they appear to be associated, directly or indirectly, with signaling proteins including IGF-1 receptor, Raf, MEK kinases and PI3-kinase, although the precise molecular mechanisms of inhibition or activation of these elements are not clear (31). Several studies have reported subregulation of the 14-3-3σ protein in breast cancer, suggesting its role as a tumor suppressor (32).…”