title: Calcineurin regulates nuclear factor I dephosphorylation and activity in malignant glioma cell lines.
abstract: Malignant gliomas (MG), including grades III and IV astrocytomas, are the most common adult brain tumors. These tumors are highly aggressive with a median survival of less than 2 years. Nuclear factor I (NFI) is a family of transcription factors that regulates the expression of glial genes in the developing brain. We have previously shown that regulation of the brain fatty acid-binding protein (B-FABP; FABP7) and glial fibrillary acidic protein (GFAP) genes in MG cells is dependent on the phosphorylation state of NFI, with hypophosphorylation of NFI correlating with GFAP and B-FABP expression. Importantly, NFI phosphorylation is dependent on phosphatase activity that is enriched in GFAP/B-FABP+ve cells. Using chromatin immunoprecipitation, we show that NFI occupies the GFAP and B-FABP promoters in NFI-hypophosphorylated GFAP/B-FABP+ve MG cells. NFI occupancy, NFI-dependent transcriptional activity, and NFI phosphorylation are all modulated by the serine/threonine phosphatase calcineurin. Importantly, a cleaved form of calcineurin, associated with increased phosphatase activity, is specifically expressed in NFI-hypophosphorylated GFAP/B-FABP+ve MG cells. Calcineurin in GFAP/B-FABP+ve MG cells localizes to the nucleus. In contrast, calcineurin is primarily found in the cytoplasm of GFAP/B-FABP-ve cells, suggesting a dual mechanism for calcineurin activation in MG. Finally, our results demonstrate that calcineurin expression is up-regulated in areas of high infiltration/migration in grade IV astrocytoma tumor tissue. Our data suggest a critical role for calcineurin in NFI transcriptional regulation and in the determination of MG infiltrative properties.
authors.affiliation: Departments of Oncology, University of Alberta, Cross Cancer Institute, Edmonton, Alberta T6G 1Z2, Canada.
authors.forename: Miranda
authors.initials: M
authors.lastname: Brun
authors.forename: Darryl D
authors.initials: DD
authors.lastname: Glubrecht
authors.forename: Shairaz
authors.initials: S
authors.lastname: Baksh
authors.forename: Roseline
authors.initials: R
authors.lastname: Godbout
mesh_terms: D000328:Adult; D001254:Astrocytoma / Q000378:metabolism / Q000473:pathology; D019703:Calcineurin / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000494:pharmacology; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D016572:Cyclosporine / Q000494:pharmacology; D005910:Glioma / Q000201:enzymology* / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D015759:Ionomycin / Q000494:pharmacology; D051839:NFI Transcription Factors / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects
chemical_list: D002135:Calcium-Binding Proteins; D051839:NFI Transcription Factors; D015759:Ionomycin; C033668:calpastatin; D016572:Cyclosporine; D019703:Calcineurin
keywords: Brain Tumors; Calcineurin; Calpain; Cancer Biology; Gene Expression; Glial Fibrillary Acidic Protein; Nuclear Factor I; Phosphorylation; Transcription