Differential regulation of two alternatively spliced isoforms of hypoxia-inducible factor-1 alpha in activated T lymphocytes.
Cell adaptation to hypoxia is partially accomplished by hypoxia-inducible transcription factor-1 (HIF-1). Here we report the hypoxia-independent up-regulation of HIF-1 alpha subunit in antigen receptor-activated T cells. This is explained by a selective up-regulation of alternatively spliced mRNA isoform I.1 that encodes the HIF-1 alpha protein without the first 12 N-terminal amino acids. We show that both short (I.1) and long (I.2) HIF-1 alpha isoforms display similar DNA binding and transcriptional activities. Major differences were observed between these two HIF-1 alpha isoforms in their expression patterns with respect to the resting and activated T lymphocytes in hypoxic and normoxic conditions. The T cell antigen receptor (TCR)-triggered activation of normal ex vivo T cells and differentiated T cells results in up-regulation of expression of I.1 isoform of HIF-1 alpha mRNA without an effect on constitutive I.2 HIF-1 alpha mRNA expression. The accumulation of I.1 HIF-1 alpha mRNA isoform in T lymphocytes is also demonstrated during cytokine-mediated inflammation in vivo, suggesting a physiological role of short HIF-1 alpha isoform in activated lymphocytes. The TCR-triggered, protein kinase C and Ca(2+)/calcineurin-mediated HIF-1 alpha I.1 mRNA induction is protein synthesis-independent, suggesting that the HIF-1 alpha I.1 gene is expressed as an immediate early response gene. Therefore, these data predict a different physiological role of short and long isoforms of HIF-1 alpha in resting and activated cells.
Lukashev
D
D
Laboratory of Immunology, NIAID, National Institutes of Health, Bethesda, Maryland 20892, USA.
Caldwell
C
C
Ohta
A
A
Chen
P
P
Sitkovsky
M
M
D017398:Alternative Splicing; D000818:Animals; D015687:Cell Hypoxia / Q000502:physiology*; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D017781:Genes, Immediate-Early / Q000502:physiology; D006801:Humans; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008213:Lymphocyte Activation; D051379:Mice; D008810:Mice, Inbred C57BL; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation
D004268:DNA-Binding Proteins; C497442:HIF1A protein, human; C497443:Hif1a protein, mouse; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D009687:Nuclear Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; D011948:Receptors, Antigen, T-Cell; D014157:Transcription Factors