Loss of Krüppel-like factor 4 expression contributes to Sp1 overexpression and human gastric cancer development and progression.
OBJECTIVE
Increasing evidence indicates that the transcription factor, Sp1, regulates the expression of multiple genes involved in tumor development and progression. We have recently reported that Sp1 overexpression is directly correlated with the angiogenic potential of and poor prognosis for human gastric cancer. However, the underlying mechanisms that result in Sp1 overexpression remain unclear.


METHODS
The expression of Sp1 and Krüppel-like factor 4 (KLF4), a potential tumor suppressor gene, in gastric cancer tissue was analyzed by immunohistochemistry and Western blot analysis. Alterations of Sp1 and KLF4 expression were achieved by gene transfer and verified by Northern and Western blot analyses. Furthermore, Sp1 promoter activity assay, electrophoretic mobility shift assay, and chromatin immunoprecipitation assay were done to identify the KLF4 binding sites on the Sp1 promoter.


RESULTS
Mutually exclusive expression of Sp1 and KLF4 was evident in gastric cancer and noncancerous tissue. Specifically, strong Sp1 expression but loss of KLF4 expression was found in cancer tissue, whereas the adjacent noncancerous tissue showed negative Sp1 expression but strong KLF4 expression. Enforced KLF4 expression repressed Sp1 expression at the promoter activity, mRNA, and protein levels. Moreover, a region within the proximal Sp1 promoter was identified to have overlapping KLF4- and Sp1-binding sites, to which KLF4 and Sp1 compete for binding. Sp1 positively regulated its own promoter, whereas KLF4 did the opposite.


CONCLUSIONS
Our data suggests that disruption of KLF4-mediated negative regulation contributes to the molecular events of Sp1 overexpression and to the development and progression of human gastric cancer.
Kanai
Masashi
M
Department of Gastrointestinal Medical Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030, USA.
Wei
Daoyan
D
Li
Qiang
Q
Jia
Zhiliang
Z
Ajani
Jaffer
J
Le
Xiangdong
X
Yao
James
J
Xie
Keping
K
D000230:Adenocarcinoma / Q000378:metabolism*; D001483:Base Sequence; D015152:Blotting, Northern; D015153:Blotting, Western; D045744:Cell Line, Tumor; D017931:DNA Primers; D024202:Electrophoretic Mobility Shift Assay; D015870:Gene Expression; D006801:Humans; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors / Q000096:biosynthesis* / Q000235:genetics; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D034741:RNA, Small Interfering; D016329:Sp1 Transcription Factor / Q000096:biosynthesis* / Q000235:genetics; D013274:Stomach Neoplasms / Q000378:metabolism*
D017931:DNA Primers; C000715467:KLF4 protein, human; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors; D034741:RNA, Small Interfering; D016329:Sp1 Transcription Factor