Analysis of purified gp96 preparations from rat and mouse livers using 2-D gel electrophoresis and tandem mass spectrometry

Glucose-regulated protein precursor (GRP78) and tumor rejection antigen (GP96) are unique to hamster caput epididymal spermatozoa

The immotile testicular mammalian spermatozoon gets transformed into a motile spermatozoon during 'epididymal maturation'. During this process, the spermatozoa transit from the caput to the cauda epididymis and undergo a number of distinct morphological, biophysical and biochemical changes, including changes in protein composition and protein modifications, which may be relevant to the acquisition of motility potential. The present proteome-based study of the hamster epididymal spermatozoa of caput and cauda led to the identification of 113 proteins spots using Matrix-assisted laser desorption/ionization tandem mass spectrometry (MALDI-MS/MS) analysis. Comparison of these 113 protein spots indicated that 30 protein spots (corresponding to 20 proteins) were significantly changed in intensity. Five proteins were increased and eleven were decreased in intensity in the cauda epididymal spermatozoa. In addition, two proteins, glucose-regulated protein precursor (GRP78) and tumor rejection antigen (GP96), were unique to the caput epididymal spermatozoa, while one protein, fibrinogen-like protein 1, was unique to cauda epididymal spermatozoa. A few of the five proteins, which increased in intensity, were related to sperm metabolism and ATP production during epididymal maturation. The changes in intensity of a few proteins such as ERp57, GRP78, GP96, Hsp60, Hsp70, and dihydrolipoamide S-acetyltransferase were validated by immunoblotting. The present study provides a global picture of the changes in protein composition occurring during hamster sperm epididymal maturation, besides being the first ever report on the proteome of hamster spermatozoa.

Caught with their PAMPs down? The extracellular signalling actions of molecular chaperones are not due to microbial contaminants

In recent years, it has been hypothesised that a new signalling system may exist in vertebrates in which secreted molecular chaperones form a dynamic continuum between the cellular stress response and corresponding homeostatic physiological mechanisms. This hypothesis seems to be supported by the finding that many molecular chaperones are released from cells and act as extracellular signals for a range of cells. However, this nascent field of biological research seems to suffer from an excessive criticism that the biological activities of molecular chaperones are due to undefined components of the microbial expression hosts used to generate recombinant versions of these proteins. In this article, a number of the proponents of the cell signalling actions of molecular chaperones take this criticism head-on. They show that sufficient evidence exists to support fully the hypothesis that molecular chaperones have cell-cell signalling actions that are likely to be part of the homeostatic mechanism of the vertebrate.

A non-receptor-mediated mechanism for internalization of molecular chaperones

The evolving realization that stress proteins, which have for many years been considered to be exclusively intracellular molecules under normal conditions, can be released from viable cells via a number of potential routes/pathways has prompted interest into their extracellular biology and intercellular signaling properties. That the stress proteins Hsp60, Hsp70 and gp96 can elicit both pro- and anti-inflammatory effects suggests that these molecules play a key role in the maintenance of immunological homeostasis, and a better understanding of the immunobiology of extracellular stress proteins might reveal new and more effective approaches for controlling and managing infectious disease, inflammatory disease and cancer. A number of cell surface receptors for stress proteins have been identified, and the intracellular consequences of these cell surface receptor-ligand interactions have been characterized. To date, studies into the intercellular signaling properties of stress proteins and their interactions with antigen presenting cells have focused on specific receptor-mediated uptake, and have not considered the fact that such cells can also take up proteins via non-specific endocytosis/pinocytosis. Herein we present a methodological approach for assessing receptor-mediated and non-receptor-mediated uptake of gp96 by rat bone marrow-derived dendritic cells.

Administration of the stress protein gp96 prolongs rat cardiac allograft survival, modifies rejection-associated inflammatory events, and induces a state of peripheral T-cell hyporesponsiveness

High-dose gp96 has been shown to inhibit experimental autoimmune disease by a mechanism that appears to involve immunoregulatory CD4+ T cells. This study tested the hypothesis that high-dose gp96 administration modifies allograft rejection and associated inflammatory events. Wistar cardiac allografts were transplanted into Lewis recipient rats and graft function was monitored daily by palpation. Intradermal administration of gp96 purified from Wistar rat livers (100 microg) at the time of transplantation and 3 days later significantly prolonged allograft survival (14 vs 8 days in phosphate-buffered saline [PBS]-treated recipients; P = 0.009). Rejected allografts from gp96-treated animals were significantly less enlarged than allografts from their PBS-treated counterparts (2.8 vs 4.3 g; P < 0.004). Gp96 was also effective when administered on days 1 and 8 (13 vs 7 days), but not if it was derived from recipient (Lewis) liver tissue or administered on days 0, 3, and 6. In parallel studies, CD3+ T cells from gp96-treated untransplanted animals secreted less interleukin (IL)-4, IL-10, and interferon (IFN)-gamma after in vitro polyclonal stimulation than CD3+ T cells from PBS-treated animals. Gp96 administration might therefore influence the induction of immunity to coencountered antigenic challenges and inflammatory events by inducing what appears to be a state of peripheral T-cell hyporesponsiveness.

The stress protein gp96 is not an activator of resting rat bone marrow-derived dendritic cells, but is a costimulator and activator of CD3+ T cells

Although low doses of tumor-derived stress protein gp96 elicit protective immunity to the tumor from which it is isolated, protection is lost at high doses because of the induction of immunoregulatory CD4+ T cells. This study evaluated the influence of gp96 on resting rat bone marrow-derived dendritic cells (BMDCs) and purified CD3+ T cells. In contrast to previous reports, gp96 had no effect on adhesion and costimulatory molecule expression by BMDCs, nor did it influence interleukin (IL)-10 and IL-12 secretion or their allostimulatory capacity. Gp96 did not bind to BMDCs but dose-dependently bound to CD4+ and CD8+ T cells. At low concentrations (1 and 25 microg/mL), gp96 acted as a costimulator of CD3+ T cells, inducing proliferation and the secretion of interferon (IFN)-gamma- and IL-10. Gp96 also increased the proliferation of CD28-costimulated CD3+ T cells and their secretion of IFN-gamma, IL-4, and IL-10. Gp96 had no effect at higher concentrations (50 and 100 microg/mL), despite the occurrence of cell surface binding at these concentrations. These findings indicate that gp96 can act as a costimulatory molecule for CD3+ T cells, and an observed increase in the IL-10: IFN-gamma secretion ratio induced by gp96 suggests that it might, at appropriate concentrations, promote a regulatory T-helper 2 (Th2)-like phenotype.