Endoplasmic reticulum stress stimulates the expression of cyclooxygenase-2 through activation of NF-κB and pp38 mitogen-activated protein kinase Free

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Expression of mutant proteins or viral infection may interfere with proper protein folding activity in the endoplasmic reticulum (ER). Several pathways that maintain cellular homeostasis are activated in response to these ER disturbances. In this report, we investigated which of these ER stress-activated pathways induce COX-2, and potentially oncogenesis. Tunicamycin and brefeldin A, two ER stress inducers, increased the expression of COX-2 in ML-1 or MCF-7 cells. Nuclear translocation of NF-κB and activation of pp38 MAP kinase was observed during ER stress. IκBα-kinase inhibitor Bay 11-7082 or IκBα kinase dominant negative mutant significantly inhibited the induction of COX-2. PP38 MAP kinase inhibitor SB-203580 or eIF2α phosphorylation inhibitor 2-aminopurine attenuated the nuclear NF-κB DNA binding activity and COX-2 induction. Expression of mutant hepatitis B virus (HBV) large surface proteins, inducers of ER stress, enhanced the expression of COX-2 in ML-1 and HuH-7 cells. Transgenic mice showed higher expression of COX-2 protein in liver and kidney tissue expressing mutant HBV large surface protein in vivo. Similarly, increased expression of COX-2 mRNA was observed in human hepatocellular carcinoma tissue expressing mutant HBV large surface proteins. In ML-1 cells expressing mutant HBV large surface protein, anchorage-independent growth was enhanced, and the enhancement was abolished by the addition of specific COX-2 inhibitors. Thus, ER stress due either to expression of viral surface proteins or drugs can stimulate the expression of COX-2 through the NF-κB and pp38 kinase pathways. Our results provide important insights into cellular carcinogenesis associated with latent endoplasmic reticulum stress. In the next, we will further want to investigate the relationship between NF-κB and p38 MAPK signaling pathway. So we will use CHIP assay to identify the NF-κB and p38 MAPK kinase and how to regulate COX-2 expression during ER stress.