BIOCHEMICAL-ANALYSIS OF THE STRESS PROTEIN RESPONSE IN HUMAN ESOPHAGEAL EPITHELIUM

Background-The oesophageal epithelium is exposed routinely to noxious agents in the environment, including gastric acid, thermal stress, and chemical toxins. These epithelial cells have presumably evolved effec tive protective mechamisms to withstand tissue damage and repair injur ed cells. Heat shock protein or stress protein responses play a centra l role in protecting distinct cell types from different types of injur y. Aim-To determine (i) whether biochemical analysis of stress protein responses in pinch biopsy specimens from human oesophageal epithelium is feasible; (ii) whether undue stresses are imposed on cells by the act of sample collection, thus precluding analysis of stress responses ; and (iii) if amenable to experimentation, the type of heat shack pro tein (Hsp) response that operates in the human oesophageal epithelium. Methods-Tissue from the human oesophagus comprised predominantly of s quamous epithelium was acquired within two hours of biopsy and subject ed to an in vitro heat shock. Soluble tissue cell lysates derived from untreated or heat shocked samples were examined using dennaturing pol yacrylamide gel electrophoresis for changes in: (i) the pattern of gen eral protein synthesis by labelling epithelial cells with S-35-methion ine and (ii) the levels of soluble Hsp70 protein and related isoforms using immunochemical protein blots. Results-A single pinch biopsy spec imen is sufficient to extract and analyse specific sets of polypeptide s in the oesophageal epithelium. After ex vivo heat shock, a classic i nhibition of general protein synthesis is observed and correlates with the increased synthesis of two major proteins of molecular weight of 60 and 70 kDa. Notably, cells from unheated controls exhibit a ''stres sed'' biochemical state 22 hours after incubation at 37 degrees C, as shown by inhibition of general protein synthesis and increased synthes is of the 70 kDa protein. These data indicate that only freshly acquir ed specimens are suitable for studying stress responses ex vivo, No ev idence was found that the two heat induced polypeptides are previously identified Hsp70 isoforms. In fact, heat shock results in a reduction in the steady state concentractions of Hsp70 protein in the oesophage al epithelium. Conclusion-Systematic and highly controlled studies on protein biochemistry are possible on epithelial biopsy specimens from the human oesophagus. These technical innovations have permitted the d iscovery of a novel heat shock response operating in the oesophageal e pithelium. Notably, two polypeptides were synthesised after heat shock that seem to differ from Hsp70 protein. In addition, the striking red uction in steady state concentrations of Hsp70 protein after heat shoc k suggests that oesophageal epithelium has evolved an atypical biochem ical response to thermal stress.