Human esophageal microvascular endothelial cells respond to acidic pH stress by PI3K/AKT and p38 MAPK-regulated induction of Hsp70 and Hsp27

Abstract

The heat shock response maintains cellular homeostasis following sublethal injury. Heat shock proteins (Hsps) are induced by thermal, oxyradical, and inflammatory stress, and they chaperone denatured intracellular proteins. Hsps also chaperone signal transduction proteins, modulating signaling cascades during repeated stress. Gastroesophageal reflux disease (GERD) affects 7% of the US population, and it is linked to prolonged esophageal acid exposure. GERD is characterized by enhanced and selective leukocyte recruitment from esophageal microvasculature, implying activation of microvascular endothelium. We investigated whether phosphatidylinositol 3-kinase (PI3K)/Akt and MAPK regulate Hsp induction in primary cultures of human esophageal microvascular endothelial cells (HEMEC) in response to acid exposure (pH 4.5). Inhibitors of signaling pathways were used to define the contribution of PI3K/Akt and MAPKs in the heat shock response and following acid exposure. Acid significantly enhanced phosphorylation of Akt and MAPKs in HEMEC as well as inducing Hsp27 and Hsp70. The PI3K inhibitor LY-294002, and Akt small interfering RNA inhibited Akt activation and Hsp70 expression in HEMEC. The p38 MAPK inhibitor (SB-203580) and p38 MAPK siRNA blocked Hsp27 and Hsp70 mRNA induction, suggesting a role for MAPKs in the HEMEC heat shock response. Thus acidic pH exposure protects HEMEC through induction of Hsps and activation of MAPK and PI3 kinase pathway. Acidic exposure increased HEMEC expression of VCAM-1 protein, but not ICAM-1, which may contribute to selective leukocyte (i.e., eosinophil) recruitment in esophagitis. Activation of esophageal endothelial cells exposed to acidic refluxate may contribute to GERD in the setting of a disturbed mucosal squamous epithelial barrier (i.e., erosive esophagitis, peptic ulceration).

Heat stress upregulates chaperone heat shock protein 70 and antioxidant manganese superoxide dismutase through reactive oxygen species (ROS), p38MAPK, and Akt

“…Therefore, p38MAPK is definitely upstream of the augmented HSF1 activity. Stresses other than heat like hypoxia (Uehara et al 1999) or low pH (Rafiee et al 2006) have been observed to raise Hsp70 levels along with an increased activity of p38MAPK. Low pH causes human esophageal endothelial cells to overexpress Hsp70 by increasing HSF1 transcriptional activity through mediation by p38MAPK and Akt (Rafiee et al 2006).…”

“…Stresses other than heat like hypoxia (Uehara et al 1999) or low pH (Rafiee et al 2006) have been observed to raise Hsp70 levels along with an increased activity of p38MAPK. Low pH causes human esophageal endothelial cells to overexpress Hsp70 by increasing HSF1 transcriptional activity through mediation by p38MAPK and Akt (Rafiee et al 2006). However, in alkalosis, increase of Hsp70 levels were not accompanied by augmented p38MAPK activation (Stathopoulou et al 2006).…”

“…Furthermore, the connection between heat-induced production of ROS and activation of p38MAPK by heat stress has not been adequately probed. Studies depicting signaling pathways upstream of stresses or stimuli other than heat are more readily available (Kim et al 2005a;Rafiee et al 2006;Stathopoulou et al 2006;Uehara et al 1999). Human esophageal microvascular endothelial cells induce Hsp70 by the Akt and p38MAPK pathways when subjected to low pH (Rafiee et al 2006).…”

“…Studies depicting signaling pathways upstream of stresses or stimuli other than heat are more readily available (Kim et al 2005a;Rafiee et al 2006;Stathopoulou et al 2006;Uehara et al 1999). Human esophageal microvascular endothelial cells induce Hsp70 by the Akt and p38MAPK pathways when subjected to low pH (Rafiee et al 2006). However, in alkalosis, p38MAPK activation is not necessary for induction of Hsp70 (Stathopoulou et al 2006).…”

Implication of PI3K-dependent HSP27 and p53 expression in mild heat shock-triggered switch of metabolic stress-induced necrosis to apoptosis in A549 cells

“…5A and B). Similarly, PI3K has been shown to participate in phosphorylation or induction of HSP27 in response to various stimuli, including acidic pH stress-induced HSP27 induction in human esophageal microvascular endothelial cells, vasopressininduced HSP27 phosphorylation in aortic smooth muscle A10 cells, and sphingosine 1-phosphate-stimulated HSP27 induction in osteoblasts (34)(35)(36). In addition, PI3K pathway has been demonstrated as the critical mediator in p53 activation in response to cisplatin (14).…”