Mouse Lactoferrin Gene

Essential role of KLF5 transcription factor in cell proliferation and differentiation and its implications for human diseases

KLF5 (Kruppel-like factor 5) is a basic transcription factor binding to GC boxes at a number of gene promoters and regulating their transcription. KLF5 is expressed during development and, in adults, with higher levels in proliferating epithelial cells. The expression and activity of KLF5 are regulated by multiple signaling pathways, including Ras/MAPK, PKC, and TGFbeta, and various posttranslational modifications, including phosphorylation, acetylation, ubiquitination, and sumoylation. Consistently, KLF5 mediates the signaling functions in cell proliferation, cell cycle, apoptosis, migration, differentiation, and stemness by regulating gene expression in response to environment stimuli. The expression of KLF5 is frequently abnormal in human cancers and in cardiovascular disease-associated vascular smooth muscle cells (VSMCs). Due to its significant functions in cell proliferation, survival, and differentiation, KLF5 could be a potential diagnostic biomarker and therapeutic target for cancer and cardiovascular diseases.

Regulation of KLF5 involves the Sp1 transcription factor in human epithelial cells

Human Kruppel-like factor 5 (hKLF5) is a transcription factor with a potential tumor suppressor function in prostate and breast cancers. In the majority of cancer samples examined, a significant loss of expression for KLF5 has been detected. Whereas hemizygous deletion appears to be responsible for KLF5's reduced expression in about half of the cases, the mechanism for reduction is unknown in the remaining half; gene promoter methylation does not appear to be involved. In this report, we studied the regulation of KLF5 and cloned and functionally characterized a 1944-bp fragment of the 5'-flanking region of the hKLF5 gene. Several mitogens as well as global demethylation induced the expression of KLF5, implicating multiple factors in the regulation of KLF5. KLF5's promoter lacks a TATA box and has a GC-rich region. Deletion mapping in combination with promoter activity assay showed that multiple cis-elements are involved in the transcriptional regulation of KLF5, some of which may play a repressor role whereas some others play an enhancer role. The Sp1 site between position -239 and -219 is essential for a basal promoter activity. Deletion or mutations of this Sp1 site significantly reduced promoter activity in several epithelial cell lines. Electrophoretic mobility shift assays (EMSAs) revealed that the Sp1 site binds Sp1 protein in nucleic extracts of different cell lines. In addition, overexpression of Sp1 protein transactivates KLF5 promoter activity. These findings suggest that Sp1 is a key transcription factor in KLF5's dynamic transcriptional regulation.

Regulation of lactoferrin gene expression by estrogen and epidermal growth factor: molecular mechanism

Lactoferrin (LF) is a member of the transferrin gene family. Its expression in the mouse uterus is regulated by estrogen and epidermal growth factor (EGF). The author et al. cloned the LF gene promoter/enhancer region, and demonstrated that multihormone signaling pathways are involved in modulating LF gene activity. Three short but complex modules, within 400 bp from the transcription initiation site of the mouse LF gene, contain the response elements that are responsible for estrogen, retinoic acid, mitogen, and growth factor stimulation. These elements have been identified and characterized, using reporter constructs transiently transfected into human endometrial carcinoma RL95-2 cells. The author et al. used molecular approaches, such as deletion, insertion, and site-directed mutagenesis, to determine the relationship between the response elements, and to fine-map the crucial nucleotides within them. This article reviews the characterization of the estrogen and EGF response elements of the mouse LF gene promoter.