title: CRABP-II methylation: a critical determinant of retinoic acid resistance of medulloblastoma cells.
abstract: Medulloblastoma cells exhibit varied responses to therapy by all-trans retinoic acid (RA). The underlying mechanism for such diverse effects however remains largely unclear. In this study, we attempted to elucidate the molecular basis of RA resistance through the study of RA signaling components in both RA-sensitive (Med-3) and RA-resistant (UW228-2 and UW228-3) medulloblastoma cells. The results revealed that RARα/β/γ and RXRα/β/γ were found in the three cell lines. Expression of CRABP-I and CRABP-II was seen in Med-3 cells, up-regulated when treated with RA, but was absent in UW228-2 and UW228-3 cells regardless of RA treatment. Bisulfite sequencing revealed 8 methylated CG sites at the promoter region of CRABP-II in UW228-2 and UW228-3 but not in Med-3 cells. Demethylation by 5-aza-2'-deoxycytidine recovered CRABP-II expression. Upon restoration of CRABP-II expression, both UW228-2 and UW228-3 cells responded to RA treatment by forming neuronal-like differentiation, synaptophysin expression, β-III tubulin upregulation, and apoptosis. Furthermore, CRABP-II specific siRNA reduced RA sensitivity in Med-3 cells. Tissue microarray-based immunohistochemical staining showed variable CRABP-II expression patterns among 104 medulloblastoma cases, ranging from negative (42.3%), partly positive (14.4%) to positive (43.3%). CRABP-II expression was positively correlated with synaptophysin (rs = 0.317; p = 0.001) but not with CRABP-I expression (p > 0.05). In conclusion, aberrant methylation in CRABP-II reduces the expression of CRABP-II that in turn confers RA resistance in medulloblastoma cells. Determination of CRABP-II expression or methylation status may enable a personalized RA therapy in patients with medulloblastomas and other types of cancers.
authors.affiliation: Liaoning Laboratory of Cancer Genomics and Department of Cell Biology, College of Basic Medical Sciences, Dalian Medical University, Dalian 116044, PR China.
authors.forename: Yuan-Shan
authors.initials: YS
authors.lastname: Fu
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.forename: Jing-Xin
authors.initials: JX
authors.lastname: Ma
authors.forename: Xiang-Hong
authors.initials: XH
authors.lastname: Yang
authors.forename: Mo-Li
authors.initials: ML
authors.lastname: Wu
authors.forename: Kai-Li
authors.initials: KL
authors.lastname: Zhang
authors.forename: Qing-You
authors.initials: QY
authors.lastname: Kong
authors.forename: Xiao-Yan
authors.initials: XY
authors.lastname: Chen
authors.forename: Yuan
authors.initials: Y
authors.lastname: Sun
authors.forename: Nan-Nan
authors.initials: NN
authors.lastname: Chen
authors.forename: Xiao-Hong
authors.initials: XH
authors.lastname: Shu
authors.forename: Hong
authors.initials: H
authors.lastname: Li
authors.forename: Jia
authors.initials: J
authors.lastname: Liu
mesh_terms: D001374:Azacitidine / Q000494:pharmacology; D001483:Base Sequence; D045744:Cell Line, Tumor; D003577:Cytochrome P-450 Enzyme System; D019175:DNA Methylation / Q000187:drug effects*; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008527:Medulloblastoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000235:genetics; D034741:RNA, Small Interfering / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000235:genetics / Q000378:metabolism*; D000072516:Retinoic Acid 4-Hydroxylase; D017422:Sequence Analysis, DNA; D015398:Signal Transduction / Q000187:drug effects; D046888:Tissue Array Analysis; D014162:Transfection; D014212:Tretinoin / Q000494:pharmacology*
chemical_list: D034741:RNA, Small Interfering; D018168:Receptors, Retinoic Acid; C082927:retinoic acid binding protein I, cellular; C082928:retinoic acid binding protein II, cellular; D014212:Tretinoin; D003577:Cytochrome P-450 Enzyme System; D000072516:Retinoic Acid 4-Hydroxylase; D001374:Azacitidine