Human NCU-G1 can function as a transcription factor and as a nuclear receptor co-activator.
BACKGROUND
Novel, uncharacterised proteins represent a challenge in biochemistry and molecular biology. In this report we present an initial functional characterization of human kidney predominant protein, NCU-G1.


RESULTS
NCU-G1 was found to be a highly conserved nuclear protein rich in proline with a molecular weight of approximately 44 kDa. It is localized on chromosome 1 and consists of 6 exons. Analysis of the amino acid sequence revealed no known transcription activation domains or DNA binding regions, however, four nuclear receptor boxes (LXXLL), and four SH3-interaction motives in addition to numerous potential phosphorylation sites were found. Two nuclear export signals were identified, but no nuclear localization signal. In man, NCU-G1 was found to be widely expressed at the mRNA level with especially high levels detected in prostate, liver and kidney. Electrophoretic mobility shift analysis showed specific binding of NCU-G1 to an oligonucleotide representing the footprint 1 element of the human cellular retinol-binding protein 1 gene promoter. NCU-G1 was found to activate transcription from this promoter and required presence of the footprint 1 element. In transiently transfected Drosophila Schneider S2 cells, we demonstrated that NCU-G1 functions as a co-activator for ligand-activated PPAR-alpha, resulting in an increased expression of a CAT reporter gene under control of the peroxisome proliferator-activated receptor-alpha responsive acyl-CoA oxidase promoter.


CONCLUSIONS
We propose that NCU-G1 is a dual-function protein capable of functioning as a transcription factor as well as a nuclear receptor co-activator.
Steffensen
Knut R
KR
Department of Molecular Biosciences, University of Oslo, Norway. knut.steffensen@biosci.ki.se
Bouzga
Mariam
M
Skjeldal
Frode
F
Kasi
Cecilie
C
Karahasan
Almira
A
Matre
Vilborg
V
Bakke
Oddmund
O
Guérin
Sylvain
S
Eskild
Winnie
W
D000595:Amino Acid Sequence; D002467:Cell Nucleus / Q000378:metabolism; D003001:Cloning, Molecular; D020869:Gene Expression Profiling; D006367:HeLa Cells; D006801:Humans; D008024:Ligands; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D009841:Oligonucleotides / Q000378:metabolism; D009928:Organ Specificity; D047493:PPAR alpha / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D021381:Protein Transport; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D054840:Retinol-Binding Proteins, Cellular / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation / Q000235:genetics
C527735:GLMP protein, human; D008024:Ligands; D009687:Nuclear Proteins; D009841:Oligonucleotides; D047493:PPAR alpha; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D054840:Retinol-Binding Proteins, Cellular; D014157:Transcription Factors