Abstract
Annexin A1 (ANXA1) down-regulation is an early and frequent event in the development of head and neck squamous cell carcinomas (HNSCC). In an attempt to identify the underlying mechanisms of reduced ANXA1 protein expression, this study investigated ANXA1 mRNA expression in HNSCC specimens by both in situ hybridization and RT-qPCR. Results showed a perfect concordance between the pattern of ANXA1 mRNA and protein detected by immunofluorescence in tumors, precancerous lesions and normal epithelia, reflecting that ANXA1 down-regulation occurs at transcriptional level. We also found that both miR-196a and miR-196b levels inversely correlated with ANXA1 mRNA levels in paired HNSCC tissue samples and patient-matched normal mucosa. In addition, endogenous levels of ANXA1 mRNA and protein were consistently and significantly down-regulated upon miR-196a and miR-196b over-expression in various HNSCC-derived cell lines. The direct interaction of both mature miR-196a and miR-196b was further confirmed by transfection with Anxa1 3′UTR constructs. Combined bioinformatics and functional analysis of ANXA1 promoter activity contributed to identify key regions and potential mediators of ANXA1 transcriptional control. This study unveils that, in addition to miR-196a, miR-196b also directly targets ANXA1 in HNSCC.
Highlights
Annexin A1 (ANXA1, known as lipocortin 1 and calpactin II) is a pleiotropic 37 kDa protein member of the annexin superfamily with roles in vesicular trafficking and the maintenance of membrane-cytoskeletal integrity[1]
We have previously reported that ANXA1 protein expression is frequently down-regulated in head and neck squamous cell carcinomas (HNSCC) tissue specimens, while highly expressed in the differentiated layers of normal epithelium[14]
We focused on the well-documented loss of ANXA1 protein expression in HNSCC14, 15, 24 by visualizing the changes using immunofluorescence microscopy
Summary
Annexin A1 (ANXA1, known as lipocortin 1 and calpactin II) is a pleiotropic 37 kDa protein member of the annexin superfamily with roles in vesicular trafficking and the maintenance of membrane-cytoskeletal integrity[1]. ANXA1 is considered a primary mediator of the anti-inflammatory, immunosuppressive actions of glucocorticoids[2] and current attention has focused on its roles in membrane remodeling and cell behavior associated with regulatory signaling via the Formyl Peptide Receptor[3] and oncogenesis[4]. These studies point to a major regulatory role for ANXA1 in cell-growth regulation and differentiation, neutrophil migration, CNS responses to cytokines, neuroendocrine secretion and apoptosis. As individual microRNAs can regulate multiple genes[17, 18] including those encoding transcription factors, we investigated the potential contribution of transcriptional control by analysis of ANXA1 promoter activity
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