Sp1 Controls the Basal Level of Interleukin-34 Transcription

ABSTRACT

Interleukin-34 (IL-34) is a cytokine that plays important roles at steady state and in diseases. The induced or inhibited expression of IL-34 by stimuli has been deeply investigated. However, the regulation of IL-34 basal expression is largely unknown. The aim of this study is to investigate whether IL-34 expression is regulated by a general transcription factor Specificity Protein 1 (Sp1) at transcription level. By using bioinformatic software, four putative Sp1-binding sites overlapping GC boxes were found in the core promoter region of IL-34. Alignment of the core promoter sequences of mammalian IL-34 showed GC box-C (−62/–57) and D (−11/–6) were conserved in some mammals. Luciferase assay results showed that only deletion of GC box-C (−62/–57) significantly reduced luciferase activities of IL-34 core promoter in SH-SY5Y cells. By using electrophoretic mobility shift assay (EMSA), it was found that Sp1 specifically interacted with GC box-C sequence CCCGCC (−62/–57) in the core promoter of IL-34. By using chromatin immunoprecipitation (ChIP), it was discovered that Sp1 bound to the core promoter of IL-34 in living cells. In addition, silencing of Sp1 expression by its specific siRNA reduced IL-34 mRNA and protein levels significantly in SH-SY5Y cells. Likewise, IL-34 expression was inhibited in a dose-dependent manner by a Sp1 inhibitor Plicamycin. Furthermore, silencing of Sp1 also downregulated mRNA and protein expression of IL-34 in GES-1 and 293T cell lines, suggesting that IL-34 transcription regulated by Sp1 was not cell-type specific. Taken together, these results indicate that Sp1 controls the basal level of IL-34 transcription.

KEYWORDS:

• IL-34
• regulation
• Sp1
• transcription

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work is supported by Natural Science Foundation of Anhui Province [Nos. 1908085MH279, 1508085MH158], Inflammation and Immune Mediated Diseases Laboratory of Anhui Province [No. IMMDL202005], National Undergraduate Training Programs for Innovation and Entrepreneurship-China [No. 201610366006], Provincial Undergraduate Training Programs for Innovation and Entrepreneurship-Anhui [No. S202110366070].