title: BAMBI is expressed in endothelial cells and is regulated by lysosomal/autolysosomal degradation.
abstract: BACKGROUND
  BAMBI (BMP and Activin Membrane Bound Inhibitor) is considered to influence TGFβ and Wnt signaling, and thereby fibrosis. Surprisingly data on cell type-specific expression of BAMBI are not available. We therefore examined the localization, gene regulation, and protein turnover of BAMBI in kidneys.
  
  
  RESULTS
  By immunofluorescence microscopy and by mRNA expression, BAMBI is restricted to endothelial cells of the glomerular and some peritubular capillaries and of arteries and veins in both murine and human kidneys. TGFβ upregulated mRNA of BAMBI in murine glomerular endothelial cells (mGEC). LPS did not downregulate mRNA for BAMBI in mGEC or in HUVECs. BAMBI mRNA had a half-life of only 60 minutes and was stabilized by cycloheximide, indicating post-transcriptional regulation due to AU-rich elements, which we identified in the 3' untranslated sequence of both the human and murine BAMBI gene. BAMBI protein turnover was studied in HUVECs with BAMBI overexpression using a lentiviral system. Serum starvation as an inducer of autophagy caused marked BAMBI degradation, which could be totally prevented by inhibition of lysosomal and autolysosomal degradation with bafilomycin, and partially by inhibition of autophagy with 3-methyladenine, but not by proteasomal inhibitors. Rapamycin activates autophagy by inhibiting TOR, and resulted in BAMBI protein degradation. Both serum starvation and rapamycin increased the conversion of the autophagy marker LC3 from LC3-I to LC3-II and also enhanced co-staining for BAMBI and LC3 in autolysosomal vesicles.
  
  
  CONCLUSIONS
  1. BAMBI localizes to endothelial cells in the kidney and to HUVECs. 2. BAMBI mRNA is regulated by post-transcriptional mechanisms. 3. BAMBI protein is regulated by lysosomal and autolysosomal degradation. The endothelial localization and the quick turnover of BAMBI may indicate novel, yet to be defined functions of this modulator for TGFβ and Wnt protein actions in the renal vascular endothelium in health and disease.
authors.affiliation: Department of Medicine, Mount Sinai School of Medicine, New York, New York, United States of America.
authors.forename: Sandhya
authors.initials: S
authors.lastname: Xavier
authors.forename: Victoria
authors.initials: V
authors.lastname: Gilbert
authors.forename: Maria Pia
authors.initials: MP
authors.lastname: Rastaldi
authors.forename: Stefanie
authors.initials: S
authors.lastname: Krick
authors.forename: Dmitrij
authors.initials: D
authors.lastname: Kollins
authors.forename: Anand
authors.initials: A
authors.lastname: Reddy
authors.forename: Erwin
authors.initials: E
authors.lastname: Bottinger
authors.forename: Clemens D
authors.initials: CD
authors.lastname: Cohen
authors.forename: Detlef
authors.initials: D
authors.lastname: Schlondorff
mesh_terms: D020413:3' Untranslated Regions; D000818:Animals; D001343:Autophagy; D002460:Cell Line; D042783:Endothelial Cells / Q000166:cytology / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000378:metabolism; D008247:Lysosomes / Q000235:genetics / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout
chemical_list: D020413:3' Untranslated Regions; C485671:BAMBI protein, human; C485672:Bambi protein, mouse; D008565:Membrane Proteins