Characterization of a functional promoter polymorphism of the human tryptophan hydroxylase 2 gene in serotonergic raphe neurons.
BACKGROUND
Tryptophan hydroxylase 2 (TPH2) is the rate-limiting enzyme in brain serotonin (5-HT) biosynthesis. Although dysfunction of 5-HT neurotransmission has been implicated in a variety of neuropsychiatric conditions, the human TPH2 promoter has not been characterized in vitro.


METHODS
The functional relevance of TPH2 promoter polymorphisms was determined with luciferase assays in primary serotonergic neurons from rat raphe nuclei and in human small cell lung carcinoma cells (SHP-77 cells). We also investigated transcription factor binding to the variant promoter sequence with electrophoretic mobility shift assay (EMSA).


RESULTS
The polymorphism rs11178997 of the human TPH2 promoter significantly reduced TPH2 transcriptional activity by 22% and 7% in primary serotonergic neurons and in SHP-77 cells, respectively. In contrast, no significant differences in promoter activity were observed for the G- and T-alleles of rs4570625. The EMSA revealed reduced binding of the transcription factor POU3F2 (also known as Brn-2, N-Oct-3) to the A-allele of the polymorphism rs11178997. Overexpression of POU3F2 resulted in a robust activation of the TPH2 promoter (2.7-fold).


CONCLUSIONS
Our data suggest that the human TPH2 promoter polymorphism rs11178997 impacts on gene expression, which might have implications for the development and function of the serotonergic system in the brain.
Scheuch
Kathrin
K
Laboratory of Molecular Psychiatry, Charité-Universitätsmedizin Berlin, Schumannstrasse 20/21, Berlin, Germany.
Lautenschlager
Marion
M
Grohmann
Maik
M
Stahlberg
Silke
S
Kirchheiner
Julia
J
Zill
Peter
P
Heinz
Andreas
A
Walther
Diego J
DJ
Priller
Josef
J
D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D018288:Carcinoma, Small Cell / Q000201:enzymology / Q000235:genetics; D045744:Cell Line, Tumor; D004273:DNA, Neoplasm / Q000235:genetics; D024202:Electrophoretic Mobility Shift Assay; D005822:Genetic Vectors; D006801:Humans; D007150:Immunohistochemistry; D008156:Luciferases / Q000378:metabolism; D009474:Neurons / Q000201:enzymology*; D011110:Polymorphism, Genetic; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D011903:Raphe Nuclei / Q000166:cytology / Q000201:enzymology*; D051381:Rats; D012701:Serotonin / Q000502:physiology*; D014162:Transfection; D014365:Tryptophan Hydroxylase / Q000235:genetics*
D004273:DNA, Neoplasm; D012333:RNA, Messenger; D012701:Serotonin; D008156:Luciferases; D014365:Tryptophan Hydroxylase; C504569:tph2 protein, rat