Regulation of mouse Scgb3a1 gene expression by NF-Y and association of CpG methylation with its tissue-specific expression

By reporter gene transfection and gel mobility shift analyses, we demonstrated that expression of the mouse Scgb3a1 gene is regulated by a PU-box binding protein and a ubiquitous transcription factor NF-Y that respectively binds to the PU-boxes located at -99 to -105 bp and -158 to -164 bp, and the "CCAAT" binding sites located at -425 to -429 bp and -498 to -502 bp from the transcription start site of the gene. However, the effect of PU-box binding protein on transcriptional activation is minimal as compared to NF-Y, suggesting that NF-Y is a more critical transcription factor for mouse Scgb3a1 gene transcription. Despite that NF-Y is a ubiquitous factor, Scgb3a1 is highly expressed only in mouse lung and mtCC cells that are derived from SV40 transformed mouse Clara cells, but not in ten other mouse tissues/cells examined. Gene methylation analysis revealed that within 600 bp of the Scgb3a1 gene promoter region, there are nine CpG methylation sites present, of which two CpGs closest to the transcription start site of the gene are unmethylated in the tissues/cells expressing SCGB3A1.A ubiquitous transcription factor NF-Y binds to and activates expression of the mouse Scgb3a1 gene and tissue-specific expression of the gene is associated with CpG methylation of the promoter.Secretoglobin (SCGB) 3A1, also called high in normal-1 (HIN-1) [1] or uteroglobin-related protein 2 (UGRP2) [2], is a member of the SCGB gene superfamily that consists of small secretory proteins [3]. HIN-1 was originally identified as a tumor suppressor gene because its expression was silenced by methylation in the majority of human breast carcinomas [1]. UGRP2 was independently identified as a homologous gene to UGRP1 (also called SCGB3A2) that is a downstream target for the homeodomain transcription factor NKX2-1, also called TITF1, TTF1, NKX2.1, or T/EBP [2]. Mouse SCGB3A1 and SCGB3A2 share 33% amino acid sequence identity [2].In humans, SCGB3A1 is highly expressed in the trachea, lung, salivar