GTP cyclohydrolase I (EC 3.5.4.16) is the first enzyme in the biosynthesis of tetrahydrobiopterin [(6R)-5,6,7,8-tetrahydro-L-biopterin, H4-biopterin] in mammals and of folic acid in bacteria. Here we have characterized the GTP cyclohydrolase I gene structure and two mRNA species from Physarum polycephalum, an acellular slime mould that synthesizes H4-biopterin and metabolites of the folic acid biosynthetic pathway. Its GTP cyclohydrolase I gene consists of seven exons, and the two GTP cyclohydrolase I cDNA species isolated from Physarum encode for proteins with 228 (25.7kDa) and 195 (22.1kDa) amino acids. Furthermore, we identified two previously undescribed mRNA species in interferon-γ-treated human myelomonocytoma cells (THP-1) in addition to the cDNA coding for the fully functional 250-residue (27.9kDa) protein, which is identical with that in human phaeochromocytoma cells. One of the new splice variants codes for a 233-residue (25.7kDa) protein, whereas the other codes for the full-length protein but is alternatively spliced within the 3′-untranslated region. In heterologous expression, the shorter proteins of Physarum as well as of THP-1 cells identified here are degraded by proteolysis. Accordingly, only the 27.9kDa protein was detectable in Western blots from THP-1 cell extracts. Quantification of GTP cyclohydrolase I mRNA species in different human cell types with and without cytokine treatment showed that in addition to the correct mRNA the two splice variants isolated here, as well as the two splice variants known from human liver, are strongly induced by cytokines in cell types with inducible GTP cyclohydrolase I (THP-1, dermal fibroblasts), but not in cell types with constitutive GTP cyclohydrolase I expression (SK-N-SH, Hep-G2). As in human liver, splicing of the new mRNA variant found in THP-1 cells occurs at the boundary of exons 5 and 6. Strikingly, the 195-residue protein from Physarum is alternatively spliced at a homologous position, i.e. at the boundary of exons 6 and 7. Thus alternative splicing of GTP cyclohydrolase I at this position occurs in two species highly distant from each other in terms of evolution. It remains to be seen whether variant proteins encoded by alternatively spliced GTP cyclohydrolase I mRNA transcripts do occur in vivo and whether they participate in regulation of enzyme activity.
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Research Article|
April 06 2001
GTP cyclohydrolase I mRNA: novel splice variants in the slime mould Physarum polycephalum and in human monocytes (THP-1) indicate conservation of mRNA processing
Georg GOLDERER;
Georg GOLDERER
*Institute of Medical Chemistry and Biochemistry, University of Innsbruck, Fritz-Pregl-Strasse 3, A-6020 Innsbruck, Austria,
‡Ludwig Boltzmann Institute of Experimental and Clinical Traumatology, Donaueschingenstrasse 13, A-1200Vienna, Austria
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Ernst R. WERNER;
Ernst R. WERNER
*Institute of Medical Chemistry and Biochemistry, University of Innsbruck, Fritz-Pregl-Strasse 3, A-6020 Innsbruck, Austria,
‡Ludwig Boltzmann Institute of Experimental and Clinical Traumatology, Donaueschingenstrasse 13, A-1200Vienna, Austria
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Christine HEUFLER;
Christine HEUFLER
†Department of Dermatology, University of Innsbruck, Anichstrasse 35, A-6020 Innsbruck, Austria,
‡Ludwig Boltzmann Institute of Experimental and Clinical Traumatology, Donaueschingenstrasse 13, A-1200Vienna, Austria
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Wolfgang STROHMAIER;
Wolfgang STROHMAIER
*Institute of Medical Chemistry and Biochemistry, University of Innsbruck, Fritz-Pregl-Strasse 3, A-6020 Innsbruck, Austria,
‡Ludwig Boltzmann Institute of Experimental and Clinical Traumatology, Donaueschingenstrasse 13, A-1200Vienna, Austria
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Peter GRÖBNER;
Peter GRÖBNER
*Institute of Medical Chemistry and Biochemistry, University of Innsbruck, Fritz-Pregl-Strasse 3, A-6020 Innsbruck, Austria,
‡Ludwig Boltzmann Institute of Experimental and Clinical Traumatology, Donaueschingenstrasse 13, A-1200Vienna, Austria
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Gabriele WERNER-FELMAYER
Gabriele WERNER-FELMAYER
1
*Institute of Medical Chemistry and Biochemistry, University of Innsbruck, Fritz-Pregl-Strasse 3, A-6020 Innsbruck, Austria,
‡Ludwig Boltzmann Institute of Experimental and Clinical Traumatology, Donaueschingenstrasse 13, A-1200Vienna, Austria
1To whom correspondence should be addressed (e-mail gabriele.werner-felmayer@uibk.ac.at).
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Publisher: Portland Press Ltd
Received:
November 14 2000
Revision Received:
January 22 2001
Accepted:
February 08 2001
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London © 2001
2001
Biochem J (2001) 355 (2): 499–507.
Article history
Received:
November 14 2000
Revision Received:
January 22 2001
Accepted:
February 08 2001
Citation
Georg GOLDERER, Ernst R. WERNER, Christine HEUFLER, Wolfgang STROHMAIER, Peter GRÖBNER, Gabriele WERNER-FELMAYER; GTP cyclohydrolase I mRNA: novel splice variants in the slime mould Physarum polycephalum and in human monocytes (THP-1) indicate conservation of mRNA processing. Biochem J 15 April 2001; 355 (2): 499–507. doi: https://doi.org/10.1042/bj3550499
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