Hypoosmotic stress activates p38, ERK 1 and 2, and SAPK/JNK in rat hepatocytes

Background, Following hepatocyte injury, changes in the perihepatocyte mili eu modulate cell volume and influence growth. Hypoosmotic stress activates nuclear factor-kappa B (NF-kappa B), a transcription factor believed to pri me cell cycle progression in hepatocytes, In this study, we investigate the role of mitogen-activated protein kinases (MAPKs) in the activation of NF- kappa B. Materials and methods. Quiescent primary hepatocytes were exposed to hypoos motic serum-free William's E (WE) medium (200 mOsm/liter), with or without a l-h pretreatment with either PD 98059 (15 mu M) or SB 202190 (3 mu M). Pa rallel experiments were conducted using hepatocyte growth factor (HGF) at 0 .1 mg/ml and normoosmotic WE medium as positive and negative controls, resp ectively (n = 3), Relative densitometries of Western blots measured phospho rylated cytoplasmic p38, ERK 1 and 2, and SAPK/JNK. Electromobility shift a ssays examined nuclear NF-kappa B activation. Results. (i) Hypoosmolar WE medium phosphorylated p38, ERK 1 and 2, and SAP K/JNK by 5 min. (ii) Hypoosmolar WE medium activated NF-kappa B at 60 min. (iii) HGF phosphorylated all three MAPKs and activated NF-kappa B with prof iles similar to those of hypoosmotic stress, (iv) Both PD 98059 and SE 2021 90 abrogated the activation of NF-kappa B in HGF-stimulated cells but not i n hypoosmotically stressed cells, Conclusion, (i) Both hypoosmotic cell swelling and HGF phosphorylate p38, E RK 1 and 2, and SAPK/JNK, and (ii) HGF, but not hypoosmotic stress, activat es NF-kappa B via p38 and ERK 1 and 2 phosphorylation. These data suggest t hat cell swelling activates NF-kappa B through a pathway separate from that of growth factors, (C) 2000 Academic Press.