Transcription factor CCAAT/enhancer-binding protein-β upregulates microRNA, let-7f-1 in human endocervical cells

Problem: In endocervical epithelial cells (End1/E6E7), miRNA let-7f plays an important role in the control of innate immunity. The underlying molecular mechanism for let-7f regulation in these cells remains largely unclear. Methods of study: let-7f was knocked down in End1/E6E7 cells using siRNA, and differential gene expression was analyzed by microarray. Differentially expressed genes were validated by qPCR and Western blot. Expression of let-7f was studied by qPCR after inhibition of C/EBP beta with betulinic acid (BA) and pCMV beta plasmid and after overexpression of C/EBP beta with pCMV beta+ plasmid. ChIP assay was performed to confirm binding of C/EBP beta to let-7f promoter. Levels of Lin28A/B were checked by qPCR after similar treatment. Results: let-7f knockdown (KD) affects the expression of many transcription factors (eg, C/EBP beta) which are important regulators of immune responses. We observed let-7f-1 promoter to contain 6 C/EBP beta binding sites. KD of C/EBP beta led to decreased let-7f expression while overexpression of C/EBP beta increased its expression. Treatment of End1/E6E7 cells with TLR-3 ligand, poly(I:C) increased binding of C/EBP beta at binding sites 3, 5, and 6. Expression of Lin28A/B also changed upon inhibition and overexpression of C/EBP beta. Its expression is opposite to that of let-7f in End1/E6E7 cells. Conclusion: let-7f-1 is a direct target of transcription factor, C/EBP beta in End1/E6E7 cells.