Ultrastructural localization of Hsp-72 examined with a new polyclonal antibody raised against the truncated variable domain of the heat shock protein

In spite of the intensive search for the determination of the continuously widening physiological and pathological roles of different stress proteins, their ultrastructural localization at the electron microscopic (EM) level has hardly been examined. As it becomes increasingly evident that the function and physiological effectiveness of stress proteins are highly dependent on their spatial location and their associations with diverse regulator proteins, the demand for morphological studies which can identify their detailed distribution within the cells is evident. The reason for the practical lack of studies carried out at the EM level, lies in the shortage of reagents with suitable specificity and avidity necessary for this type of examination. To create such a reagent, a polyclonal antibody was raised using a recombinant truncated form of the inducible Hsp-72 protein. The antibody was extensively characterized, using different immunochemical methods to determine and verify its specificity, and then it was tried in ultrastructural examinations. Using the new antibody, it was possible to analyze the intracellular distribution of Hsp-72 with the immunogold technique. The localization of Hsp-72 was demonstrated directly at the ultrastructural level in the cytoplasm (especially at the cisterns of the RER), in the nucleus (mainly around the heterochromatic regions) and at both sides of the nuclear envelope close to the membrane pores. Apart from these localizations, Hsp-72 was found in several membrane bordered intracellular structures, which mainly belong to the endosomal-lysosomal system. We provide the first morphological verification of the appearance of Hsp-72 on the surface of the cells. Also novel is the indication, that the stress protein may recycle from the cell surface using a common route which includes coated pits and the endosomal system.