Cell confluency-induced Stat3 activation regulates NHE3 expression by recruiting Sp1 and Sp3 to the proximal NHE3 promoter region during epithelial dome formation

Hsiao Wen Su, Shainn Wei Wang, Fayez K. Ghishan, Pawel R. Kiela, Ming Jer Tang

Research output: Contribution to journalReview article

19 Scopus citations


Activation of signal transducer and activator of transcription-3 (Stat3) during cell confluency is related to its regulatory roles in cell growth arrest- or survival-related physiological or developmental processes. We previously demonstrated that this signaling event triggers epithelial dome formation by transcriptional augmentation of sodium hydrogen exchanger-3 (NHE3) expression. However, the detailed molecular mechanism remained unclear. By using serial deletions, site-directed mutagenesis, and EMSA analysis, we now demonstrate Stat3 binding to an atypical Stat3-response element in the rat proximal NHE3 promoter, located adjacent to a cluster of Sp cis-elements (SpA/B/C), within -77/-36 nt of the gene. SpB (-58/-55 nt) site was more effective than SpA (-72/-69 nt) site for cooperative binding of Sp1/Sp3. Increasing cell density had no effect on Sp1/Sp3 expression but resulted in their increased binding to the SpA/B/C probe along with Stat3 and concurrently with enhanced nuclear pTyr705-Stat3 level. Immunoprecipitation performed with the nuclear extracts demonstrated physical interaction of Stat3 and Sp1/Sp3 triggered by cell confluency. Stat3 inhibition by overexpression of dominant-negative Stat3-D mutant in MDCK cells or by small interfering RNA-mediated knockdown in Caco-2 cells resulted in inhibition of the cell density-induced NHE3 expression, Sp1/Sp3 binding, and NHE3 promoter activity and in decreased dome formation. Thus, during confluency, ligand-independent Stat3 activation leads to its interaction with Sp1/Sp3, their recruitment to the SpA/B/C cluster in a Stat3 DNA-binding domain-dependent fashion, increased transcription, and expression of NHE3, to coordinate cell density-mediated epithelial dome formation.

Original languageEnglish (US)
Pages (from-to)C13-C24
JournalAmerican Journal of Physiology - Cell Physiology
Issue number1
StatePublished - Jan 1 2009



  • Dome formation
  • Na/H exchanger-3
  • Signal transducer and activator of transcription-3
  • Slc9a3

ASJC Scopus subject areas

  • Physiology
  • Cell Biology

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