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1.  TAK1 mediates BMP signaling in cartilage 
Although many signals are capable of activating MAPK signaling cascades in chondrocytes in vitro, the function of these pathways remains unclear in vivo. Here we report the phenotype of mice with a conditional deletion of TGF-β-activated kinase 1 (TAK1), a MAP3K family member, in cartilage using the collagen 2α promoter. These mice display chondrodysplasia characterized by neonatal-onset runting, delayed formation of secondary ossification centers, and defects in formation of the elbow and tarsal joints. This constellation of defects resembles the phenotype of mice deficient for receptors or ligands involved in signaling by BMP family members. Chondrocytes from these mice show evidence of defective BMP signaling in vivo and in vitro. Surprisingly, deletion of TAK1 seems to affect not only activation of the p38 MAPK signaling cascade, but also activation of the BMP-responsive Smad1/5/8. Biochemical analysis suggests that TAK1 can interact with Smad proteins and promote their activation through phosphorylation, revealing a previously unrecognized crosstalk between the MAPK and Smad arms of BMP signaling.
PMCID: PMC3096020  PMID: 20392264
BMP; cartilage; TAK1; TGF-β; Smad
2.  From Sugar to Fat 
Annals of the New York Academy of Sciences  2009;1173(Suppl 1):E2-E9.
Lipogenesis occurs primarily in the liver, where dietary carbohydrates control the expression of key enzymes in glycolytic and lipogenic pathways. We have recently discovered that the transcription factor XBP1, best known as a key regulator of the unfolded protein response (UPR), is required for de novo fatty acid synthesis in the liver, a function unrelated to its role in the UPR.1 XBP1 protein expression is induced in the liver by a high carbohydrate diet and directly controls the induction of critical genes involved in fatty acid synthesis. Specific deletion of XBP1 in adult liver using an inducible approach results in profound hypocholesterolemia and hypotriglyceridemia, which could be attributed to diminished production of lipids in the liver. Notably, this phenotype is not associated with fatty liver (hepatic steatosis) or significant compromise in protein secretion. XBP1 joins an already rich field of transcriptional regulatory proteins in the control of hepatic lipogenesis. Its function in lipogenesis appears to be highly significant as evidenced by the phenotype of the genetic mutant strain. A more complete understanding of the mechanisms by which XBP1 accelerates de novo fatty acid synthesis in the liver while preserving normal hepatic lipid composition is highly relevant to the treatment of diseases such as atherosclerosis and metabolic syndrome that are associated with dyslipidemia. Since excess fat accumulation in the liver could result from increased hepatic fatty acid synthesis, compounds that inhibit XBP1 activation may also be useful therapeutics for the treatment of human alcoholic liver disease (ALD) and nonalcoholic fatty liver disease (NAFLD), increasingly common causes of morbidity and mortality in the United States.
PMCID: PMC3096021  PMID: 19751410
XBP1; liver; lipogenesis; dyslipidemia; transcription; triglycerides; cholesterol

Results 1-2 (2)