Flavia Contino

The PVT-1 oncogene is a myc protein target that is overexpressed in transformed cells

The human PVT‐1 gene is located on chromosome 8 telomeric to the c‐Myc gene and it is frequently involved in the translocations occurring in variant Burkitts lymphomas and murine plasmacytomas. It has been proposed that PVT‐1 regulates c‐Myc gene transcription over a long distance. To get new insights into the functional relationships between the two genes, we have investigated PVT‐1 and c‐Myc expression in normal human tissues and in transformed cells. Our findings indicate that PVT‐1 expression is restricted to a relative low number of normal tissues compared to the wide distribution of c‐Myc mRNA, whereas the gene is highly expressed in many transformed cell types including neuroblastoma cells that do not express c‐Myc. Reporter gene assays were used to dissect the PVT‐1 promoter and to identify the region responsible for the elevated expression observed in transformed cells. This region contains two putative binding sites for Myc proteins. The results of transfection experiments in RAT1‐MycER cells and chromatin immunoprecipitation (ChIP) assays in proliferating and differentiated neuroblastoma cells indicate that PVT‐1 is a downstream target of Myc proteins. J. Cell. Physiol. 213: 511–518, 2007.

Myc Promoter-Binding Protein-1 (MBP-1) Is a Novel Potential Prognostic Marker in Invasive Ductal Breast Carcinoma

Background Alpha-enolase is a glycolytic enzyme that catalyses the formation of phosphoenolpyruvate in the cell cytoplasm. α-Enolase and the predominantly nuclear Myc promoter-binding protein-1 (MBP-1) originate from a single gene through the alternative use of translational starting sites. MBP-1 binds to the P2 c-myc promoter and competes with TATA-box binding protein (TBP) to suppress gene transcription. Although several studies have shown an antiproliferative effect of MBP-1 overexpression on several human cancer cells, to date detailed observations of α-enolase and MBP-1 relative expression in primary tumors versus normal tissues and their correlation with clinicopathological features have not been undertaken. Methodology and Findings We analyzed α-enolase and MBP-1 expression in normal breast epithelium and primary invasive ductal breast carcinoma (IDC) from 177 patients by Western blot and immunohistochemical analyses, using highly specific anti-α-enolase monoclonal antibodies. A significant increase in the expression of cytoplasmic α-enolase was observed in 98% of the tumors analysed, compared to normal tissues. Nuclear MBP-1 was found in almost all the normal tissues while its expression was retained in only 35% of the tumors. Statistically significant associations were observed among the nuclear expression of MBP-1 and ErbB2 status, Ki-67 expression, node status and tumor grade. Furthermore MBP-1 expression was associated with good survival of patients with IDC. Conclusions MBP-1 functions in repressing c-myc gene expression and the results presented indicate that the loss of nuclear MBP-1 expression in a large number of IDC may be a critical step in the development and progression of breast cancer and a predictor of adverse outcome. Nuclear MBP-1 appears to be a novel and valuable histochemical marker with potential prognostic value in breast cancer.

Negative transcriptional control of ERBB2 gene by MBP-1 and HDAC1: diagnostic implications in breast cancer

BackgroundThe human ERBB2 gene is frequently amplified in breast tumors, and its high expression is associated with poor prognosis. We previously reported a significant inverse correlation between Myc promoter-binding protein-1 (MBP-1) and ERBB2 expression in primary breast invasive ductal carcinoma (IDC). MBP-1 is a transcriptional repressor of the c-MYC gene that acts by binding to the P2 promoter; only one other direct target of MBP-1, the COX2 gene, has been identified so far.MethodsTo gain new insights into the functional relationship linking MBP-1 and ERBB2 in breast cancer, we have investigated the effects of MBP-1 expression on endogenous ERBB2 transcript and protein levels, as well as on transcription promoter activity, by transient-transfection of SKBr3 cells. Reporter gene and chromatin immunoprecipitation assays were used to dissect the ERBB2 promoter and identify functional MBP-1 target sequences. We also investigated the relative expression of MBP-1 and HDAC1 in IDC and normal breast tissues by immunoblot analysis and immunohistochemistry.ResultsTransfection experiments and chromatin immunoprecipitation assays in SKBr3 cells indicated that MBP-1 negatively regulates the ERBB2 gene by binding to a genomic region between nucleotide −514 and −262 of the proximal promoter; consistent with this, a concomitant recruitment of HDAC1 and loss of acetylated histone H4 was observed. In addition, we found high expression of MBP-1 and HDAC1 in normal tissues and a statistically significant inverse correlation with ErbB2 expression in the paired tumor samples.ConclusionsAltogether, our in vitro and in vivo data indicate that the ERBB2 gene is a novel MBP-1 target, and immunohistochemistry analysis of primary tumors suggests that the concomitant high expression of MBP-1 and HDAC1 may be considered a diagnostic marker of cancer progression for breast IDC.

Cellular stress induces cap‐independent alpha‐enolase/MBP‐1 translation

Myc promoter‐binding protein‐1 (MBP‐1) is a shorter protein variant of the glycolytic enzyme alpha‐enolase. Although several lines of evidence indicate that MBP‐1 acts as a tumor suppressor, the cellular mechanisms and signaling pathways underlying MBP‐1 expression still remain largely elusive. To dissect these pathways, we used the SkBr3 breast cancer cell line and non‐tumorigenic HEK293T cells ectopically overexpressing alpha‐enolase/MBP‐1. Here, we demonstrate that induced cell stresses promote MBP‐1 expression through the AKT/PERK/eIF2α signaling axis. Our results contribute to shedding light on the molecular mechanisms underlying MBP‐1 expression in non‐tumorigenic and cancer cells.