Peptidoglycan Recognition Protein Tag7 Forms a Cytotoxic Complex with Heat Shock Protein 70 in Solution and in Lymphocytes

Abstract

The peptidoglycan recognition protein Tag7 is shown to form a stable 1:1 complex with the major stress protein Hsp70. Neither protein is cytotoxic by itself, but their complex induces apoptotic death in several tumorderived cell lines even at subnanomolar concentrations. The minimal part of Hsp70 needed to evoke cytotoxicity is residues 450 -463 of its peptide-binding domain, but full cytotoxicity requires its ATPase activity; remarkably, Tag7 liberated from the complex at high ATP is not cytotoxic. The Tag7-Hsp70 complex is produced by tag7-transfected cells and by lymphokine-activated killers, being assembled within the cell and released into the medium through the Golgi apparatus by a mechanism different from the commonly known granule exocytosis. Thus, we demonstrate how a heat shock protein may perform functions clearly distinct from chaperoning or cell rescue and how peptidoglycan recognition proteins may be involved in innate immunity and anti-cancer defense.

A new role for PGRP-S (Tag7) in immune defense: lymphocyte migration is induced by a chemoattractant complex of Tag7 with Mts1

“…Our data have deepened the insight into the functional activity of Tag7 in the immune defense, showing that it forms stable complexes with Hsp70 and the Ca 2C binding protein Mts1, 9,18 with the functions of these complexes being completely different from those of their components. Indeed, the Tag7-Hsp70 complex can kill tumor cells, thereby retarding tumor growth, while Tag7 alone has no cytotoxic activity.…”

“…9 Stimulation of cytotoxic T lymphocytes by cancer cells leads to the production and secretion of the same complex, which has similar activity against tumor cells. 9, 17 Moreover, we have found 2 additional proteins that can interact with Tag7: the Ca 2C -binding protein S100A4 (Mts1), encoded by the gene that is highly expressed in metastatic tumors and cells of the immune system, and the cochaperone HspBP1, which inhibits the ATPase activity of Hsp70.…”

“…8 We have detected this protein in human T lymphocytes. 9,10 Murine PGRP-S contained in neutrophil granules has been shown to inhibit the growth of Gram-positive bacteria in the culture medium. 11 PGRP-S-deficient mice are highly vulnerable to bacterial infections, and their neutrophils cannot kill the bacteria they phagocytize.…”

Gene transfer approaches in cancer immunotherapy

“…75 There are small extracellular proteins (19)(20)(21)(22)(23)(24), which structurally share homology with T phage lyzozyme but do not possess any amidaze activity. Apart from their ability to recognize oligosaccharides and particularly peptidoglycan 70,75 cytotoxicity towards mammalian cells, 69,75,76 bactericidal and bacteriostatic activities 75 were detected. Tag7/PGRP-S is expressed in the spleen, brain, intestine, 69,74,77 bone marrow, 70 in lymphocytes 78 and neutrophils.…”

Zebrafish peptidoglycan recognition protein SC (zfPGRP-SC) mediates multiple intracellular signaling pathways

“…In contrast to insect PGRP-S, mammalian PGRP-S functions as an intracellular antibacterial protein in PMNs [12], and is directly bactericidal and bacteriostatic, but it is not an amidase [13]. The soluble form of mouse tag7/PGRP can also trigger apoptosis in mouse L929 cells [14], and initiate the cytotoxic events complexed with Hsp70 [15].…”