Activation of bile acid biosynthesis by the p38 mitogen-activated protein kinase (MAPK): hepatocyte nuclear factor-4alpha phosphorylation by the p38 MAPK is required for cholesterol 7alpha-hydroxylase expression.

Bile acids are required for intestinal absorption and biliary solubilization of cholesterol and lipids. In addition, bile acids play a crucial role in cholesterol homeostasis. One of the key enzymes in the bile acid biosynthetic pathways is cholesterol 7alpha-hydroxylase/cytochrome P450 7alpha-hydroxylase (7alpha-hydroxylase), which is the rate-limiting and regulatory step of the "classic" pathway. Transcription of the 7alpha-hydroxylase gene is highly regulated. Two nuclear receptors, hepatocyte nuclear factor 4alpha (HNF-4alpha) and alpha(1)-fetoprotein transcription factor, are required for both transcription and regulation by different physiological events. It has been shown that some mitogen-activated protein kinases, such as the c-Jun N-terminal kinase and the ERK, play important roles in the regulation of 7alpha-hydroxylase transcription. In this study, we show evidence that the p38 kinase pathway plays an important role in 7alpha-hydroxylase expression and hence in bile acid synthesis. Inhibition of p38 kinase activity in primary hepatocytes results in approximately 5-10-fold reduction of 7alpha-hydroxylase mRNA. This suppression is mediated, at least in part, through HNF-4alpha. Inhibition of p38 kinase activity diminishes HNF-4alpha nuclear protein levels and its phosphorylation in vivo and in vitro, and it renders a less stable protein. Induction of the p38 kinase pathway by insulin results in an increase in HNF-4alpha protein and a concomitant induction of 7alpha-hydroxylase expression that is blocked by inhibiting the p38 pathway. These studies show a functional link between the p38 signaling pathway, HNF-4alpha, and bile acid synthesis.

Catalase from the white shrimp Penaeus (Litopenaeus) vannamei: molecular cloning and protein detection.

Catalase is an antioxidant enzyme that plays a very important role in the protection against oxidative damage by breaking down hydrogen peroxide. It is a very highly conserved enzyme that has been identified from numerous species including bacteria, fungi, plants and animals, but the information about catalase in crustaceans is very limited. A cDNA containing the complete coding sequence for catalase from the shrimp Penaeus (Litopenaeus) vannamei was sequenced and the mRNA was detected by RT-PCR in selected tissues. Catalase was detected in hepatopancreas crude extracts by Western blot analysis with anti-human catalase polyclonal antibodies. The nucleotide sequence is 1692 bp long, including a 72-bp 5'-UTR, a coding sequence of 1515 bp and a 104-bp 3'-UTR. The deduced amino acid sequence corresponds to 505 amino acids with high identity to invertebrate, vertebrate and even bacterial catalases and contains the catalytic residues His71, Asn144, and Tyr354. The predicted protein has a calculated molecular mass of 57 kDa; which coincides with the size of the subunit (approximately 55 kDa) and the tetrameric protein (approximately 230 kDa) detected in hepatopancreas extracts under native conditions. Catalase mRNA level was higher in hepatopancreas, followed by gills and was not detected in muscle.