HER-2/neu transcriptionally activates Jab1 expression via the AKT/beta-catenin pathway in breast cancer cells.
Jab1 is a co-activator of activating protein-1 (AP-1) transcription factor and the fifth subunit of the constitutive photomorphogenesis 9 (COP9) signalosome, which has been shown to mediate nuclear exportation and ubiquitin-dependent degradation of the tumor suppressor p27(Kip1). Jab1 is overexpressed in several types of human cancer. However, de-regulation of Jab1 gene expression in cancer cells is largely unclear. In this study, we reported that expression of Jab1 was stimulated by HER-2/neu oncogene via transcriptional activation. Promoter deletion and mutation analysis indicated that HER-2/neu stimulated Jab1 via the T cell factor (TCF) binding site located at the -380/-368 region of the human Jab1 promoter. DNA affinity precipitation assay and chromatin immunoprecipitation assay verified that binding of beta-catenin and TCF-4 to this consensus site was increased by HER-2/neu. In addition, dominant-negative mutant of TCF significantly attenuated the stimulatory effect of HER-2/neu. We also demonstrated that HER-2/neu increased beta-catenin/TCF-mediated Jab1 expression via the AKT signaling pathway because chemical inhibitor or dominant-negative mutant of AKT effectively attenuated the stimulatory action of HER-2/neu. IGF-I, which is a well-known AKT activator, also up-regulated the expression of Jab1 in NIH/3T3 and MCF-7 cells. Knockdown of Jab1 by small interfering RNA (siRNA) preferentially inhibited proliferation of HER-2/neu-overexpressing breast cancer cells. Taken together, our results suggest that HER-2/neu transcriptionally activates Jab1 expression to promote proliferation of breast cancer cells.
Hsu
Ming-Chuan
MC
College of Medicine, Graduate Institute of Medicine, Kaohsiung Medical University, Kaohsiung 807, Taiwan.
Chang
Hui-Chiu
HC
Hung
Wen-Chun
WC
D000818:Animals; D001665:Binding Sites; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D000075686:COP9 Signalosome Complex; D049109:Cell Proliferation; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics*; D051379:Mice; D041681:NIH 3T3 Cells; D051058:Oncogene Protein v-akt / Q000502:physiology*; D010447:Peptide Hydrolases / Q000235:genetics*; D011401:Promoter Regions, Genetic; D034741:RNA, Small Interfering / Q000494:pharmacology; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000502:physiology*; D015398:Signal Transduction; D051820:TCF Transcription Factors / Q000378:metabolism; D015533:Transcriptional Activation; D014162:Transfection; D014407:Tumor Cells, Cultured; D051176:beta Catenin / Q000502:physiology*
D000075686:COP9 Signalosome Complex; D047908:Intracellular Signaling Peptides and Proteins; D051058:Oncogene Protein v-akt; D010447:Peptide Hydrolases; D034741:RNA, Small Interfering; D018719:Erb-b2 Receptor Tyrosine Kinases; D051820:TCF Transcription Factors; D051176:beta Catenin; C495270:CTNNB1 protein, human; C501488:COPS5 protein, human