Alternative splicing variant of the hypoxia marker carbonic anhydrase IX expressed independently of hypoxia and tumour phenotype.
CA IX is a hypoxia-induced, cancer-associated carbonic anhydrase isoform with functional involvement in pH control and cell adhesion. Here we describe an alternative splicing variant of the CA9 mRNA, which does not contain exons 8-9 and is expressed in tumour cells independently of hypoxia. It is also detectable in normal tissues in the absence of the full-length transcript and can therefore produce false-positive data in prognostic studies based on the detection of the hypoxia- and cancer-related CA9 expression. The splicing variant encodes a truncated CA IX protein lacking the C-terminal part of the catalytic domain. It shows diminished catalytic activity and is intracellular or secreted. When overexpressed, it reduces the capacity of the full-length CA IX protein to acidify extracellular pH of hypoxic cells and to bind carbonic anhydrase inhibitor. HeLa cells transfected with the splicing variant cDNA generate spheroids that do not form compact cores, suggesting that they fail to adapt to hypoxic stress. Our data indicate that the splicing variant can functionally interfere with the full-length CA IX. This might be relevant particularly under conditions of mild hypoxia, when the cells do not suffer from severe acidosis and do not need excessive pH control.
Barathova
M
M
Centre of Molecular Medicine, Institute of Virology, Slovak Academy of Sciences, Dubravska cesta 9, Bratislava 845 05, Slovak Republic.
Takacova
M
M
Holotnakova
T
T
Gibadulinova
A
A
Ohradanova
A
A
Zatovicova
M
M
Hulikova
A
A
Kopacek
J
J
Parkkila
S
S
Supuran
C T
CT
Pastorekova
S
S
Pastorek
J
J
D017398:Alternative Splicing; D000951:Antigens, Neoplasm / Q000235:genetics* / Q000378:metabolism; D014408:Biomarkers, Tumor / Q000235:genetics* / Q000378:metabolism; D000071231:Carbonic Anhydrase IX; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology; D002256:Carbonic Anhydrases / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D006801:Humans; D000860:Hypoxia / Q000235:genetics* / Q000378:metabolism; D015151:Immunoblotting; D047468:Immunoprecipitation; D009369:Neoplasms / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D010641:Phenotype; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured
D000951:Antigens, Neoplasm; D014408:Biomarkers, Tumor; D002257:Carbonic Anhydrase Inhibitors; D012333:RNA, Messenger; C089226:CA9 protein, human; D000071231:Carbonic Anhydrase IX; D002256:Carbonic Anhydrases