A PRELIMINARY-STUDY OF THE EXPRESSION OF THE HUMAN HTID PROTEIN, A HOMOLOG OF THE DROSOPHILA-MELANOGASTER TUMOR-SUPPRESSOR TID56, IN VARIOUS TUMORS

Background - DnaJ chaperones are conserved throughout evolution. Altho ugh members of this class of proteins show structural diversity they a ll share sequence homology with the bacterial dnaJ gene product. The p resence of the N-terminal J-domain, mediating the ATPase activity of H SP70 in Escherichia coli and the yeast Saccharomyces cerevisiae, defin e them as DnaJ-like proteins. A few human relatives of DnaJ have been identified to date. In no case, however, are data concerning their fun ction(s) available. Interestingly, malfunction of the recently identif ied Drosophila melanogaster dnaJ homologous tumor suppressor gene leth al(2)tumorous imaginal discs (1(2)tid), causes different developmental abnormalities including neoplastic transformation of imaginal discs, which are the adult integumental primordia. The tumorous imaginal disc s are incapable of differentiation and grow into lethal tumors, killin g the host. Based on the fact that several of the Drosophila tumor sup pressor genes cloned to date show not only structural but also functio nal homology to human genes, we carried out preliminary experiments to determine whether there are any indications that the human homolog of the 1(2)tid gene product, designated below as hTid, may also be assoc iated with neoplastic transformation. Methods - The hTid protein was i dentified by Western blotting in extracts derived from non-tumorous hu man tissue such as the liver, lung and colon and in human serum. For i mmunohistochemistry, formalin-fixed paraffin-embedded sections of huma n tissue taken from patients with various cancers were used. Immunosta ining was carried out using a polyclonal rabbit antibody to hTid, anti -hTid[pp], raised against the polypeptide EAYEVLSDKHKREIYD correspondi ng to the most conserved part of the J-domain of all DnaJ-like protein s known to date, and with the polyclonal rabbit anti-hTid antibody gen erated against the putative Drosophila melanogaster Tid56 protein. Res ults - Both the antibodies, anti-hTid[pp] and anti-Tid, used in this s tudy recognize one specific band of 50 kDa in Western blots. Visibly h igher expression of hTid was detected in tumor cells derived from aden ocarcinoma of the colon and endometrium as well as in mammary, lung an d cervix carcinomas. Immunostaining for hTid in human sarcomas, lympho mas, and melanomas yielded negative results. Conclusion - The 50-kDa p rotein detected in Western blot analysis represents the human homolog of the Drosophila melanogaster Tid56 protein. The fact that some tumor cells are characterized by visibly higher hTid levels in comparison w ith normal cells implies that hTid may be associated with either tumor development or progression. Thus recognition of abnormal levels of hT id could serve as an indicator of the pathological state of cells.