ABSTRACT
Brn-3b transcription factor enhances proliferation of neuroblastoma (NB) and breast cancer cell lines in vitro and increases the rate and size of in vivo tumour growth, whereas reducing Brn-3b slows growth, both in vitro and in vivo. Brn-3b is elevated in >65% of breast cancer biopsies, and here we demonstrate that Brn-3b is also elevated in NB tumours. We show a significant correlation between Brn-3b and cyclin D1 (CD1) in breast cancers and NB tumours and cell lines. Brn-3b directly transactivates the CD1 promoter in co-transfection experiments, whereas electrophoretic mobility shift assay and chromatin immunoprecipitation assays demonstrate that Brn-3b protein binds to an octamer sequence located in the proximal CD1 promoter. Site-directed mutagenesis of this sequence resulted in loss of transactivation of the CD1 promoter by Brn-3b. Thus, Brn-3b may act to alter growth properties of breast cancer and NB cells by enhancing CD1 expression in these cells.
Subject(s)
Breast Neoplasms/metabolism , Cyclin D1/genetics , Cyclin D1/metabolism , Gene Expression Regulation, Neoplastic , Neuroblastoma/metabolism , Transcription Factor Brn-3B/physiology , Transcriptional Activation , Breast Neoplasms/pathology , Cell Line, Tumor , Cyclin D1/biosynthesis , Female , Humans , Neuroblastoma/pathology , RNA, Messenger/biosynthesis , RNA, Messenger/metabolism , Transcription Factor Brn-3B/biosynthesis , Transcription Factor Brn-3B/genetics , Tumor Cells, Cultured , Up-Regulation/physiologyABSTRACT
IL-2 induces growth, differentiation, and/or apoptosis of lymphoid cells. To study further the molecular basis of IL-2 function, we used a cDNA subtraction approach involving a cell line grown in IL-2 or IL-4. From the corresponding library, 66 nonredundant sequences were characterized; 16 of them encode identified proteins. The kinetics of in vitro expression of 8 selected sequences, the functions of which could be associated with IL-2-induced T cell activation/differentiation, was investigated using an IL-2-dependent T cell line. IL-2 increased the expression of cytoskeleton proteins (alpha-tubulin), oncogene-regulating proteins (CCCTC-binding factor, Jun inhibitor factor-1), and transcription factors (E2F-4, cyclic AMP-responsive element-binding protein, zhx-1). IL-2 also regulated the expression of genes coding for multifunctional proteins, e.g., beta-catenin and nucleolin. These results were verified using Con A-induced T cell blasts stimulated or not by IL-2. The in vivo expression of four of these genes was also analyzed in spleen and lymph node cells of IL-2-deficient and MRL/lpr mice, which both have high numbers of activated cells, but the latter have intact IL-2 expression. The expression of beta-catenin, CCCTC-binding factor, Jun inhibitor factor-1, and nucleolin was significantly higher in MRL/lpr animals. A similar analysis of thymocytes from IL-2-/- and IL-2+/- mice demonstrated the same expression patterns of the 4 sequences in these strains. The expression of the IL-2-induced genes described herein is similar to the regulatory pattern of IL-2R alpha. Taken together, our data provide additional evidence for the pleiotropic action of IL-2 in the periphery and IL-2 independence of molecular processes involved in thymocyte differentiation.
