title: Sam68 up-regulation correlates with, and its down-regulation inhibits, proliferation and tumourigenicity of breast cancer cells.
abstract: The biosynthesis and metabolism of RNA play important roles in regulating gene expression. On the other hand, it has been shown that RNA expression profiling is differentially distinct between cancer and normal cells, suggesting the possibility that aberrant regulation of RNA metabolism might be associated with the development and progression of cancer. In the current study, we found that Sam68, an RNA-binding protein that links cellular signalling to RNA processing, was markedly overexpressed in breast cancer cells and tissues. Immunohistochemical analysis showed that the expression and cytoplasmic localization of Sam68 significantly correlated with clinical characteristics of patients, including clinical stage, tumour-nodule-metastasis (TNM) classification, histological grade, and ER expression. Univariate and multivariate analyses showed that the expression level and cytoplasmic localization of Sam68 were identified as independent prognostic factors. Furthermore, we found that siRNA knockdown of endogenous Sam68 inhibited cell proliferation and tumourigenicity of breast cancer cells in vitro, through blocking the G1 to S phase transition. Moreover, we demonstrated that the anti-proliferative effect of silencing Sam68 on breast cancer cells was associated with up-regulation of cyclin-dependent kinase inhibitor p21(Cip1) and p27(Kip1), enhanced transactivation of FOXO factors, and attenuation of Akt/GSK-3β signalling. Taken together, our results suggest that Sam68 might play an important role in promoting the proliferation and carcinogenesis of human breast cancer, and thereby might be a novel and useful prognostic marker and a potential target for human breast cancer treatment.
authors.affiliation: State Key Laboratory of Oncology in Southern China, Department of Experimental Research, Cancer Center, Sun Yat-sen University, Guangzhou, Guangdong, China. lb.song1@gmail.com
authors.forename: Libing
authors.initials: L
authors.lastname: Song
authors.forename: Lan
authors.initials: L
authors.lastname: Wang
authors.forename: Yun
authors.initials: Y
authors.lastname: Li
authors.forename: Huaping
authors.initials: H
authors.lastname: Xiong
authors.forename: Jueheng
authors.initials: J
authors.lastname: Wu
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.forename: Mengfeng
authors.initials: M
authors.lastname: Li
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000328:Adult; D014408:Biomarkers, Tumor / Q000378:metabolism*; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D049109:Cell Proliferation; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015536:Down-Regulation; D005260:Female; D051858:Forkhead Transcription Factors / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D006801:Humans; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000378:metabolism; D009367:Neoplasm Staging; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D014408:Biomarkers, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins; D051858:Forkhead Transcription Factors; C489559:KHDRBS1 protein, human; D009363:Neoplasm Proteins; D016601:RNA-Binding Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D051057:Proto-Oncogene Proteins c-akt