Cellular and Molecular Mechanisms of Heat Stress-Induced Up-Regulation of Occludin Protein Expression

Abstract

The heat stress (HS)-induced increase in occludin protein expression has been postulated to be a protective response against HS-induced disruption of the intestinal epithelial tight junction barrier. The aim of this study was to elucidate the cellular and molecular processes that mediate the HS-induced up-regulation of occludin expression in Caco-2 cells. Exposure to HS (39°C or 41°C) resulted in increased expression of occludin protein; this was preceded by an increase in occludin mRNA transcription and promoter activity. HS-induced activation of heat shock factor-1 (HSF-1) resulted in cytoplasmic-to-nuclear translocation of HSF-1 and binding to its binding motif in the occludin promoter region. HSF-1 activation was associated with an increase in occludin promoter activity, mRNA transcription, and protein expression; which were abolished by the HSF-1 inhibitor quercetin. Targeted The intestinal epithelial barrier consists of apical plasma membrane of the enterocytes that acts as a transcellular barrier and intercellular tight junctions (TJs) that act as a paracellular barrier against intercellular penetration of toxic luminal substances, including bacterial endotoxins, bacterial by-products, digestive enzymes, and food-degradation products.1-6 The TJ complex consists of cytoplasmic and transmembrane proteins. The transmembrane proteins, which include occludin, claudin family of proteins, and junctional adhesion molecules, extend from cytoplasmic compartment across the plasma membrane into extracellular compartment to participate in the formation of an extracellular TJ seal.7-10 The critical role of transmembrane proteins in the formation and maintenance of the TJ barrier is well established; however, the precise protein structure and components and molecular determinants of TJ barrier remain unclear. 11Occludin is an integral transmembrane TJ protein that has been shown to play a crucial role in TJ barrier function and TJ signaling process. Previous studies have shown that overexpression of occludin protein in MDCK cells leads to an enhancement of TJ barrier function. 12Conversely, siRNA knock-down of occludin leads to an increase in TJ permeability to selected paracellular markers. 13 Molecular studies have shown that COOH-terminal end of occludin plays a crucial role in the maintenance of paracellular barrier function.14 Additionally, biochemical alteration of occludin phosphorylation has been shown to be an important determinant of TJ localization of occludin protein and enhancement of TJ barrier function.

Short-term exposure to heat stress attenuates appetite and intestinal integrity in growing pigs1

“…As early as 8 to 12 h, these authors reported occludin protein expression to be increased in Caco-2 cells while ZO-1 is decreased. Additionally, occludin expression in Caco-2 cells exposed to 41°C was increased as early as 4 h while ZO-1 started to decrease at 6 h (Dokladny et al, 2008). These data suggest that changes in mRNA abundance of tight junction proteins due to HS may be more related to the protein phenotype than transcriptional.…”

Chronic Obstructive Pulmonary Disease – Chaperonopathology

“…There is compelling data to support a direct link between liver HSP70 accumulation and altered survival and inflammatory cytokine profile seen in heat-conditioned animals undergoing endotoxin stress. Human peripheral blood macrophages overexpressing HSP70 also inhibited lipopolysaccharide induced production of TNF-, IL-1 , IL-10 and IL-12 (Ding et al, 2001;Dokladny et al, 2008). These data taken as a whole demonstrates, that HSP70 expression is sufficient to alter proinflammatory cytokine production and increase endotoxin tolerance.…”

Heat acclimation: Gold mines and genes

“…31,32 HSPs also maintain junctional proteins that are responsible for intestinal wall integrity, thus preventing endotoxin release from the intestine which is a main contributor of the heat shock response. 42 HSPs also enhance immune function while providing resistance against inflammatory cytokines.…”