phosphothreonine and Skin-Neoplasms

BNIP2 and Cdc42GAP homology (BCH) motif-containing molecule at the carboxyl-terminal region 1 (BMCC1) gene is highly expressed in patients with favorable neuroblastoma (NB). It encodes a 340-kDa protein with a conserved BCH scaffold domain that may regulate signaling networks and multiple cellular functions, including apoptosis. In this study, we determined the mechanism by which BMCC1 promotes apoptosis in human NB and non-NB cells, as BMCC1 is normally expressed in various organs, particularly in neuronal and epithelial tissues. We demonstrated in this report that BMCC1 was induced by DNA damage, one of the triggers of intrinsic apoptosis. Accordingly, we investigated whether BMCC1 expression impacts intracellular signals in the regulation of apoptosis via its C-terminal region containing BCH scaffold domain. BMCC1 decreased phosphorylation of survival signals on AKT and its upstream kinase PDK1. BMCC1 upregulation was correlated with the activation of forkhead box-O3a (FOXO3a) (a downstream inducer of apoptosis, which is suppressed by AKT) and induction of BCL2 inhibitor BIM, suggesting that BMCC1 negatively regulates phosphorylation pathway of AKT, resulted in apoptosis. In addition, we found that BNIP2 homology region of BMCC1 interacts with BCL2. Intrinsic apoptosis induced by DNA damage was enhanced by BMCC1 overexpression, and was diminished by knockdown of BMCC1. Taken together, we conclude that BMCC1 promotes apoptosis at multiple steps in AKT-mediated survival signal pathway. These steps include physical interaction with BCL2 and attenuation of AKT-dependent inhibition of FOXO3a functions, such as transcriptional induction of BIM and phosphorylation of ataxia telangiectasia-mutated (ATM) after DNA damage. We propose that downregulation of BMCC1 expression, which is frequently observed in unfavorable NB and epithelial-derived cancers, may facilitate tumor development by abrogating DNA damage repair and apoptosis.

Topics: Apoptosis; Apoptosis Regulatory Proteins; Bcl-2-Like Protein 11; Cell Line, Tumor; Cisplatin; DNA Damage; Down-Regulation; Epithelium; Forkhead Box Protein O3; Forkhead Transcription Factors; Gene Knockdown Techniques; Humans; Membrane Proteins; Neoplasm Proteins; Neuroblastoma; Phosphorylation; Phosphothreonine; Protein Binding; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Proto-Oncogene Proteins c-bcl-2; RNA, Small Interfering; Skin Neoplasms

Merkel cell carcinoma (MCC) is a highly aggressive skin cancer with an increasing incidence. The understanding of the molecular carcinogenesis of MCC is limited. Here, we scrutinized the PI3K/AKT pathway, one of the major pathways activated in human cancer, in MCC. Immunohistochemical analysis of 41 tumor tissues and 9 MCC cell lines revealed high levels of AKT phosphorylation at threonine 308 in 88% of samples. Notably, the AKT phosphorylation was not correlated with the presence or absence of the Merkel cell polyoma virus (MCV). Accordingly, knock-down of the large and small T antigen by shRNA in MCV positive MCC cells did not affect phosphorylation of AKT. We also analyzed 46 MCC samples for activating PIK3CA and AKT1 mutations. Oncogenic PIK3CA mutations were found in 2/46 (4%) MCCs whereas mutations in exon 4 of AKT1 were absent. MCC cell lines demonstrated a high sensitivity towards the PI3K inhibitor LY-294002. This finding together with our observation that the PI3K/AKT pathway is activated in the majority of human MCCs identifies PI3K/AKT as a potential new therapeutic target for MCC patients.

Topics: Antigens, Polyomavirus Transforming; Base Sequence; Carcinoma, Basal Cell; Carcinoma, Merkel Cell; Cell Line, Tumor; Chromones; DNA Mutational Analysis; Enzyme Activation; Humans; Molecular Sequence Data; Morpholines; Mutation; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Phosphothreonine; Proto-Oncogene Proteins c-akt; Signal Transduction; Skin Neoplasms

MicroRNAs-221 and -222 are highly upregulated in several solid tumors, including melanomas. We demonstrate that the proto-oncogene ETS-1, involved in the pathogenesis of cancers of different origin, is a transcriptional regulator of miR-222 by direct binding to its promoter region. Differently from 293FT cells or early stage melanomas, where unphosphorylated ETS-1 represses miR-222 transcription, in metastatic melanoma the constitutively Thr-38 phosphorylated fraction of ETS-1 induces miR-222. Despite its stepwise decreased expression along with melanoma progression, the oncogenic activity of ETS-1 relies on its RAS/RAF/ERK-dependent phosphorylation status more than on its total amount. To close the loop, we demonstrate ETS-1 as a direct target of miR-222, but not miR-221, showing the novel option of their uncoupled functions. In addition, a spatial redistribution of ETS-1 protein from the nucleus to the cytoplasm is also evidenced in advanced melanoma cells. Finally, in vivo studies confirmed the contribution of miR-222 to the increased invasive potential obtained by ETS- silencing.

Topics: Animals; Cell Line, Tumor; Down-Regulation; Gene Expression Regulation, Neoplastic; Humans; Melanocytes; Melanoma; Mice; Mice, Nude; MicroRNAs; Neoplasm Metastasis; Phosphorylation; Phosphothreonine; Proto-Oncogene Mas; Proto-Oncogene Protein c-ets-1; Signal Transduction; Skin Neoplasms; Tetradecanoylphorbol Acetate; Transcription, Genetic