CpG island demethylation and recruitment of SP1 to the promoter region regulates human thymic stromal lymphopoietin expression

Thymic Stromal Lymphopoietin (TSLP), an immunomodulatory cytokine, plays a pivotal role in the development and progression of atopic and allergic diseases. Atopy follows familial inheritance, and genome-wide studies have shown association of atopy with TSLP polymorphisms. Here, we analysed the conserved transcriptional regulatory elements in the human TSLP promoter, which revealed the presence of three CpG islands. Demethylation of the CpG island using 5-azacytidine or siRNA-mediated knockdown of DNA methyl transferases significantly upregulated TSLP expression. Sequence analysis revealed the presence of two overlapping SP1 transcription factor DNA-binding sites (DBSs), between -1494 and -1510 nucleotides on the human TSLP promoter. Further experiments showed that demethylation of the CpG island enables the binding of SP1 to its cognate DBS present on the TSLP promoter, resulting in its transcriptional activation. Moreover, retinoic acid-induced transcription of human TSLP was associated with CpG island demethylation and SP1 binding to the TSLP promoter. These findings unravel a distinct mechanism of transcriptional regulation of the human TSLP gene and suggest possible epigenetic regulation of TSLP expression in modulating atopic and allergic disease severity in different individuals.