title: Proteasome inactivation promotes p38 mitogen-activated protein kinase-dependent phosphatidylinositol 3-kinase activation and increases interleukin-8 production in retinal pigment epithelial cells.
abstract: Oxidative stress and inflammation are implicated in the pathogenesis of many age-related diseases. We have demonstrated previously that oxidative inactivation of the proteasome is a molecular link between oxidative stress and overexpression of interleukin (IL)-8. Here, we elucidated a novel signaling cascade that leads to up-regulation of IL-8 in response to proteasome inactivation. The sequence of events in this cascade includes proteasome inactivation, activation of mitogen-activated protein kinase kinase (MKK)3/MKK6, activation of p38 mitogen-activated protein kinase (MAPK), epidermal growth factor receptor phosphorylation, phosphatidylinositol 3-kinase (PI3K) activation and increased IL-8 expression. Blocking any of these signaling pathways abolished the up-regulation of IL-8 induced by proteasome inhibition. Although Akt is also activated in response to proteasome inactivation, we found that the PI3K-dependent up-regulation of IL-8 is independent of 3-phosphoinositide-dependent protein kinase (PDK)1 and Akt. Inhibition of PDK1 and Akt with chemical inhibitors or expression of constitutive active Akt had little effects on IL-8 expression in response to proteasome inactivation. In contrast, inhibition of interleukin 2-inducible T cell kinase, a kinase downstream of PI3K, significantly reduced the expression and secretion of IL-8 in response to proteasome inactivation. Together, these data elucidate a novel signaling network that leads to increased IL-8 production in response to proteasome inactivation.
authors: Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111, USA.
authors: Alexandre F
authors: AF
authors: Fernandes
authors: Qingning
authors: Q
authors: Bian
authors: Jian-Kang
authors: JK
authors: Jiang
authors: Craig J
authors: CJ
authors: Thomas
authors: Allen
authors: A
authors: Taylor
authors: Paulo
authors: P
authors: Pereira
authors: Fu
authors: F
authors: Shang
mesh_terms: D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D066246:ErbB Receptors / Q000378:metabolism; D006801:Humans; D016209:Interleukin-8 / Q000378:metabolism*; D048371:MAP Kinase Kinase 3 / Q000378:metabolism; D048669:MAP Kinase Kinase 6 / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000166:cytology*; D015398:Signal Transduction / Q000502:physiology; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
chemical_list: D016209:Interleukin-8; D061988:Proteasome Inhibitors; D019869:Phosphatidylinositol 3-Kinases; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; C080813:emt protein-tyrosine kinase; D051057:Proto-Oncogene Proteins c-akt; D048051:p38 Mitogen-Activated Protein Kinases; D048371:MAP Kinase Kinase 3; D048669:MAP Kinase Kinase 6; D046988:Proteasome Endopeptidase Complex