ABSTRACT
UNLABELLED: Secretin stimulates ductal secretion by interacting with secretin receptor (SR) activating cyclic adenosine 3',5'-monophosphate/cystic fibrosis transmembrane conductance regulator/chloride bicarbonate anion exchanger 2 (cAMPâCFTRâCl(-) /HCO 3- AE2) signaling that is elevated by biliary hyperplasia. Cholangiocytes secrete several neuroendocrine factors regulating biliary functions by autocrine mechanisms. Melatonin inhibits biliary growth and secretin-stimulated choleresis in cholestatic bile-duct-ligated (BDL) rats by interaction with melatonin type 1 (MT1) receptor through down-regulation of cAMP-dependent signaling. No data exist regarding the role of melatonin synthesized locally by cholangiocytes in the autocrine regulation of biliary growth and function. In this study, we evaluated the (1) expression of arylalkylamine N-acetyltransferase (AANAT; the rate-limiting enzyme for melatonin synthesis from serotonin) in cholangiocytes and (2) effect of local modulation of biliary AANAT expression on the autocrine proliferative/secretory responses of cholangiocytes. In the liver, cholangiocytes (and, to a lesser extent, BDL hepatocytes) expressed AANAT. AANAT expression and melatonin secretion (1) increased in BDL, compared to normal rats and BDL rats treated with melatonin, and (2) decreased in normal and BDL rats treated with AANAT Vivo-Morpholino, compared to controls. The decrease in AANAT expression, and subsequent lower melatonin secretion by cholangiocytes, was associated with increased biliary proliferation and increased SR, CFTR, and Cl(-) /HCO 3- AE2 expression. Overexpression of AANAT in cholangiocyte cell lines decreased the basal proliferative rate and expression of SR, CFTR, and Cl(-) /HCO 3- AE2 and ablated secretin-stimulated biliary secretion in these cells. CONCLUSION: Local modulation of melatonin synthesis may be important for management of the balance between biliary proliferation/damage that is typical of cholangiopathies. (HEPATOLOGY 2013).
Subject(s)
Arylalkylamine N-Acetyltransferase/metabolism , Autocrine Communication/physiology , Bile Ducts, Intrahepatic/cytology , Bile Ducts, Intrahepatic/enzymology , Cholestasis/metabolism , Cholestasis/pathology , Animals , Anion Transport Proteins/genetics , Anion Transport Proteins/metabolism , Antioxidants/metabolism , Antioxidants/pharmacology , Antiporters/genetics , Antiporters/metabolism , Apoptosis/drug effects , Apoptosis/physiology , Arylalkylamine N-Acetyltransferase/genetics , Autocrine Communication/drug effects , Bile Ducts, Intrahepatic/drug effects , Cell Line, Transformed , Cell Proliferation , Gene Knockdown Techniques , Male , Melatonin/blood , Melatonin/pharmacology , Mice , Proliferating Cell Nuclear Antigen/genetics , Proliferating Cell Nuclear Antigen/metabolism , Rats , Rats, Inbred F344 , Receptors, Serotonin/genetics , Receptors, Serotonin/metabolism , SLC4A ProteinsABSTRACT
PURPOSE: Anthrax Lethal Toxin (LeTx), composed of protective antigen and lethal factor, catalytically cleaves mitogen-activated protein kinase (MAPK) kinases and inhibits the MAPK signaling pathways. The majority of metastatic melanomas possess the V599E BRAF mutation, which constitutively activates MAPK1/2 signaling. LeTx is cytotoxic to BRAF mutant melanoma cell lines in vitro, whereas most normal cells are resistant to this toxin. In this study, we determine the in vivo potency and safety of systemically administered LeTx. EXPERIMENTAL DESIGN: A s.c. xenograft melanoma model in athymic nude mice was treated with different i.p. doses of LeTx. RESULTS: In this study, we show that in vivo systemic LeTx treatment of s.c. xenograft melanoma tumors in athymic nude mice yields partial and complete tumor regressions with minor toxicity to mice. When animal toxicity was observed, we did not find any histologic evidence of tissue damage. CONCLUSIONS: LeTx is one of the rare targeted agents to produce complete remissions of human melanomas in an animal model and thus warrants further preclinical development.
