Open AccessCyclic AMP stimulates Mrp2 translocation by activating p38α MAPK in hepatic cells
Author(s) -
Christopher M. Schonhoff,
Cynthia R. L. Webster,
M. Sawkat Anwer
Publication year - 2010
Publication title -
american journal of physiology. gastrointestinal and liver physiology/american journal of physiology: gastrointestinal and liver physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.644
H-Index - 169
eISSN - 1522-1547
pISSN - 0193-1857
DOI - 10.1152/ajpgi.00506.2009
Subject(s) - mapk/erk pathway , wortmannin , protein kinase a , p38 mitogen activated protein kinases , transfection , microbiology and biotechnology , kinase , chemistry , biology , pi3k/akt/mtor pathway , signal transduction , biochemistry , gene
Cyclic AMP (cAMP) induces translocation of multidrug resistant protein 2 (Mrp2) to the canalicular membrane and activates p38 MAPK in rat hepatocytes. In this study, we tested the hypothesis that cAMP-induced Mrp2 translocation may be mediated via p38 MAPK. Studies were conducted in rat hepatocytes and in a human hepatoma cell line, HuH-7. In rat hepatocytes, cAMP increased Mrp2 translocation and p38 MAPK activity. These effects of cAMP were inhibited by SB203580, an inhibitor of p38 MAPK. Wortmannin, a specific inhibitor of phosphoinositide-3-kinase (PI3K), did not inhibit cAMP induced activation of p38 MAPK, indicating PI3K-independent activation of p38 MAPK by cAMP. To further define the role of p38 MAPK, molecular approaches were used to up- or downregulate p38 MAPK activity in HuH-7 cells using constitutively active (CA) and dominant-negative (DN) MAPK kinase 3 and 6 (MKK3/6). MKK3/6 are upstream kinases responsible for the activation of p38 MAPK. Cells transfected with CAMKK6 showed increased p38 MAPK activity and MRP2 translocation compared with empty vector. cAMP-induced activation of p38 MAPK was inhibited in cells transfected with DNMKK3/6 and DNMKK3, but not with DNMKK6. DNMKK3/6 and DNMKK3 also inhibited cAMP-induced MRP2 translocation. cAMP selectively activated p38alpha MAPK in HuH-7 cells. Knockdown of p38alpha MAPK by short heterodimer RNA resulted in decreased level of p38 MAPK and failure of cAMP to stimulate MRP2 translocation. Taken together, these results suggest that cAMP-induced MRP2 translocation in hepatic cells is mediated via PI3K-independent and MKK3-mediated activation of p38alpha MAPK.