MAD2 downregulation in hypoxia is independent of promoter hypermethylation.
Aberrant expression of the MAD2 protein has been linked to chromosomal instability, malignant transformation and chemoresistance. Although reduced MAD2 expression is well recognised in human cancer cell lines, the mechanism(s) underlying its downregulation remain elusive. The objective of this study was to establish the impact of hypoxia on MAD2 expression and to investigate the potential role of aberrant promoter methylation as a possible mechanism of MAD2 downregulation. For this purpose, three ovarian cancer cell lines, displaying differing levels of MAD2, were treated with chromatin modifying drugs, pre and post-hypoxia exposure and a DHPLC analysis of DNA promoter methylation carried out. We show that hypoxia induces downregulation of MAD2 expression, independently of MAD2 promoter methylation. We also show no evidence of MAD2 promoter methylation in breast and prostate cancer cells or in breast cancer clinical material. While our findings provide no evidence for MAD2 promoter methylation, we show a concomitant upregulation of p21 with downregulation of MAD2 in hypoxia. Our in vitro results were also confirmed in an ovarian cancer tissue microarray (TMA), where a reciprocal staining of MAD2 and CAIX was found in 21/60 (35%) of tumours. In summary, MAD2 downregulation may be a crucial mechanism by which hypoxic cells become chemorefractory. This stems from our previous work where we demonstrated that MAD2 downregulation induces cellular senescence, a viable cellular fate, with resultant cellular resistance to paclitaxel. Moreover, MAD2 downregulation could play a central role in the induction of chemoresistance in hypoxia, a key tumour microenvironment associated with chemoresistance.
Prencipe
Maria
M
UCD School of Medicine and Medical Science (SMMS), University College Dublin, Belfield, Dublin, Ireland. maria.prencipe@ucd.ie
McGoldrick
Aloysius
A
Perry
Antoinette S
AS
O'Grady
Anthony
A
Phelan
Sine
S
McGrogan
Barbara
B
Fitzpatrick
Patricia
P
Watson
Jenny A
JA
Furlong
Fiona
F
Brennan
Donal J
DJ
Lawler
Mark
M
Kay
Elaine
E
McCann
Amanda
A
D000951:Antigens, Neoplasm / Q000378:metabolism; D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D019175:DNA Methylation; D000077209:Decitabine; D015536:Down-Regulation; D006801:Humans; D064246:Mad2 Proteins; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology
D000951:Antigens, Neoplasm; D002135:Calcium-Binding Proteins; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; C577697:MAD2L1 protein, human; D064246:Mad2 Proteins; D012097:Repressor Proteins; D000077209:Decitabine; C089226:CA9 protein, human; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases; D001374:Azacitidine