Transcription of SST2 somatostatin receptor gene in human pancreatic cancer cells is altered by single nucleotide promoter polymorphism.
OBJECTIVE
The somatostatin receptor SST2 mediates the antiproliferative effect of stable somatostatin analogues. SST2 gene expression is lost in most human pancreatic carcinomas. We investigated the mechanisms that could be involved in this defect.


METHODS
SST2 gene structure was investigated by sequencing and restriction fragment length polymorphism. Characterization of the polymorphism was performed by electrophoretic mobility shift, cross-linking, and transcription assays.


RESULTS
No major deletion of the SST2 coding sequence was found in pancreatic carcinoma specimens, but 2 point mutations were frequently detected in the promoter sequence at positions -83 (A-->G) and -57 (C-->G) from the major transcription initiation site. These mutations were present in pancreatic cancer but also in normal pancreatic tissues or leukocytes and thus correspond to a genetic polymorphism. In the 2 human pancreatic cancer cell lines MiaPaCa-2 and AsPC-1, the naturally occurring mutation -57G had no effect on transcription of SST2 gene, whereas -83G mutation reduced it by 60%-70%. We showed that the -83G mutation creates a specific binding site for the nuclear factor I. Cotransfection experiments showed that the nuclear factor I-A1.1 isoform was responsible for SST2 promoter repression.


CONCLUSIONS
The -83G polymorphism identified on human SST2 gene promoter is responsible for the specific fixation of nuclear factor I and repression of SST2 transcription in human pancreatic cancer cells. However, its contribution to pancreatic tumorigenesis remains unknown.
Torrisani
J
J
INSERM Unité 531, Centre Hospitalier Universitaire Rangueil, Toulouse, France.
Bouisson
M
M
Puente
E
E
Capellà
G
G
Laurent-Puig
P
P
Berger
A
A
Vaysse
N
N
Susini
C
C
Buscail
L
L
D020121:5' Untranslated Regions / Q000235:genetics; D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins; D017353:Gene Deletion; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D066298:In Vitro Techniques; D009154:Mutation / Q000235:genetics; D051839:NFI Transcription Factors; D009687:Nuclear Proteins; D010179:Pancreas / Q000502:physiology; D010190:Pancreatic Neoplasms; D020641:Polymorphism, Single Nucleotide; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D017481:Receptors, Somatostatin / Q000235:genetics*; D014157:Transcription Factors; D014158:Transcription, Genetic / Q000502:physiology*; D014407:Tumor Cells, Cultured; D051840:Y-Box-Binding Protein 1
D020121:5' Untranslated Regions; D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D051839:NFI Transcription Factors; D009687:Nuclear Proteins; D012333:RNA, Messenger; D017481:Receptors, Somatostatin; D014157:Transcription Factors; D051840:Y-Box-Binding Protein 1; C070856:YBX1 protein, human; C093733:somatostatin receptor 2