Abstract
Bone morphogenetic protein-7 (BMP7) is an endogenous antifibrogenic protein in the kidney which is down regulated in experimental chronic kidney diseases such as obstructive and diabetic nephropathy in parallel with progressively increasing TGFβ. In vitro studies were performed in Madin-Darby Canine Kidney (MDCK)-cells to identify transcriptional regulators of BMP7. Experiments with various BMP7 promoter fragments (465-4,267 bp) identify small proximal promoter segments that are transcriptionally activated by high glucose (3.2-fold) but down regulated by TGFβ (0.2-fold) compared to normal glucose. Protein binding to these DNA segments is increased by high glucose and decreased by TGFβ in a time-dependent, progressive manner. Analysis of BMP7 promoter-binding proteins with liquid chromatography/tandem mass spectrometry (LC/MS/MS) identifies seven unique, partially overlapping peptides, spanning 25% of the amino acid sequence of Y-box protein-1 (YB1). EMSA-Western blot combination experiments confirm that YB1 is a BMP7 promoter-binding protein. YB1 knock-down reduces transcriptional responses to high glucose and TGFβ by about one-half, respectively. In addition, high glucose induces but TGFβ reduces nuclear translocation of YB1 from the cytoplasm. These studies identify YB1 as a transcriptional activator of BMP7 and helps to explain the progressive decline in renal BMP7 in diabetic nephropathy and other kidney diseases.