Less degradation, more shock, please

994 EDITORIALS

GASTROENTEROLOGY Vol. 116, No. 4

26. Lee A, Chen M. Successful immunization against gastric infection with Helicobacter species: use of a cholera toxin B-subunit-wholecell vaccine. Infect Immun 1994;62:3594–3597. 27. Blanchard TG, Lycke N, Czinn SJ, Nedrud JG. Recombinant cholera toxin B subunit is not an effective mucosal adjuvant for oral immunization of mice against H. felis. Immunology 1998;94: 22–27. 28. Wu HY, Russell MW. Induction of mucosal and systemic immune responses by intranasal immunization using recombinant cholera toxin B subunit as an adjuvant. Vaccine 1998;16:286–292. 29. Ågren LC, Ekman L, Lo¨wenadler B, Lycke NY. Genetically engineered nontoxic vaccine adjuvant that combines B cell targeting with immunomodulation by cholera toxin A1 subunit. J Immunol 1997;158:3936–3946. 30. Ågren LC, Ekman L, Lo¨wenadler B, Nedrud JG, Lycke NY. Adjuvanticity of the cholera toxin A1-based gene fusion protein, CTA1-DD, is critically dependent on the ADP-ribosylatransferase and Igbinding activity. J Immunol 1999;162:2432–2440. 31. Guy B, Hessler C, Fourage S, Haensler J, Vialon-Lafay E, Rokbi B, Millet M-JQ. Systemic immunization with urease protects mice against Helicobacter pylori infection. Vaccine 1998;16:850–856.

32. Lee A. Therapeutic immunization against Helicobacter infection (editorial). Gastroenterology 1996;110:2003–2006. 33. Michetti P, Corthesy-Thelaz I, Davin C, Haas R, Vaney A-C, Heitz M, Bille J, Kraehenbuhl JP, Saraga E, Blum AL. Immunization of Balb/c mice against Helicobacter felis infection with Helicobacter pylori urease. Gastroenterology 1994;107:1002–1011. 34. Mohammadi M, Czinn S, Redline R, Nedrud J. Helicobacterspecific cell-mediated immune responses display a predominant TH1 phenotype and promote a DTH response in the stomachs of mice. J Immunol 1996;156:4729–4738.

Address requests for reprints to: Steven J. Czinn, M.D., Department of Pediatrics and Pathology, Case Western Reserve University, RB&C Hospital, 11100 Euclid Avenue, Cleveland, Ohio 44106. Fax: (216) 368-1357. Supported by grant DK-46461 and AI40701 from the National Institutes of Health. r 1999 by the American Gastroenterological Association 0016-5085/99/$10.00

Less Degradation, More Shock, Please See article on page 865.

decade or so ago, the intracellular degradation of proteins was considered to be largely a housekeeping function. However, in recent years, in part due to use of inhibitors of the ubiquitin-proteasome pathway, intracellular proteolysis has been shown to be a highly dynamic process that plays a key role in regulating a variety of critical cellular processes, including cell division and growth and the cellular response to external stimuli.1 These days, it seems that one can hardly open a journal without coming across an article implicating the proteasome in some aspect of cellular function. In fact, a cursory search of the literature over the past 2 years turned up almost 100 review articles discussing proteasomedependent proteolysis. The proteasome is the major neutral proteolytic apparatus in mammalian cells involved in the degradation of the bulk of both short- and long-lived cellular proteins.1 Degradation of proteins by the proteasome is a highly regulated, adenosine triphosphate (ATP)-dependent, multistep enzymatic process. Proteasome-dependent degradation has been found to be involved in the regulation of cell functions by affecting either the amounts and/or half-lives of many important cellular regulatory proteins. The latter include the transcription factors c-jun, c-fos, I␬B␣/nuclear factor (NF)-␬B, c-myc, and DPl; the cell cycle regulators cyclin A, cyclin B, and p27; the tumor-

A

suppressor protein p53; and other proteins.2 Importantly, proteasome-dependent degradation has been found to play a critical role in the immune response via NF-␬B. NF-␬B, which regulates a number of genes involved in the immune and inflammatory response, is synthesized as a 105-kilodalton protein that is processed by the proteasome to a 50-kilodalton mature form (p50).3 p50 can then associate with several different proteins to form heterodimers that potentiate the transcription of immune and inflammatory response genes. I␬B␣ associates with the p50 heterodimer to inactivate the complex and keep it in the cytosol. Signaling via a number of cytokines induces the phosphorylation, ubiquitination, and proteasome-dependent degradation of I␬B␣, releasing the NF-␬B heterodimer, which is then free to enter the nucleus and activate the transcription of immune response genes (e.g., E-selectin, vascular cell adhesion molecule [VCAM], and intercellular adhesion molecule [ICAM]).3 Based on these findings, as well as numerous other results, it is clear that proteasome-dependent protein degradation plays a critical role not only in long-term turnover of cellular proteins but also in the regulation of a number of crucial cellular processes over the short term. These findings raise the exciting possibility that inhibition or modulation of proteasome function could have therapeutic and clinical relevance. In this issue of GASTROENTEROLOGY, Brand et al.4 report that treatment of rats (either orally or intravenously) with proteasome inhibitors effectively pre-

April 1999

vented the development of indomethacin-induced gastropathy. Using several different classes of proteasome inhibitors, they found that blockage of proteasomedependent protein degradation protects against the nonsteroidal anti-inflammatory drug (NSAID)-induced increases in mucosal ICAM expression, which has been implicated in the enhanced binding of neutrophils to microvascular endothelial cells leading to NSAIDinduced gastropathy.4 Brand et al. attribute the protection arising from treatment with proteasome inhibitors to the ability of various agents to block the proteasomedependent proteolysis of I␬B␣, which is part of the pathway involved in the stimulation of ICAM expression after indomethacin treatment. As they point out, there are other possibilities: heat-shock protein–mediated cytoprotection could be involved because inhibitors of the proteasome have been found to induce the expression of cytosolic and organellar stress proteins.5,6 The signal for the generation of a stress response is the accumulation of misfolded and/or abnormal proteins in either the cytosol (i.e., heat-shock response) or organelles (i.e., endoplasmic reticulum [ER] stress response). The stress response leads to the transcriptional induction of a family of proteins in either the cytosol or organelles, which function as molecular chaperones involved in the folding, assembly, and/or degradation of proteins.7,8 Presumably because inhibition of the proteasome should lead to the accumulation of proteins targeted for degradation, treatment of renal epithelial cells with agents that block proteasome-dependent proteolysis signals the induction of cytosolic heat-shock proteins and ER molecular chaperones.5,6 The induction of the cellular stress proteins was not found in cells treated with inactive forms of the inhibitors and was found to protect the cells from subsequent thermal injury.5,6 Thus, inhibition of the proteasome not only interferes with the degradation of a number of important cellular regulatory proteins, including I␬B␣, but it also leads to the initiation of a cellular stress response and cytoprotection. Based on these findings, as Brand et al. state, it is difficult to eliminate the possibility that induction of the stress proteins plays a crucial role in the prevention of NSAID-induced gastropathy after indomethacin treatment. As described previously, proteasome inhibition induces both a cytosolic stress response (i.e., increased expression of cytosolic heat-shock proteins), as well as an ER stress response (i.e., increased expression of the ER glucoseregulated proteins).5 The glucose-regulated proteins (Grp) belong to a family of ER molecular chaperones (i.e., Grp78/BiP, Grp94, ERp72, and others) involved in the folding and assembly of membrane and secreted proteins during their maturation in the ER.8–10 Although the role

EDITORIALS 995

of cytosolic stress proteins such as Hsp70 in cytoprotection has been well documented, the contribution of stress proteins from other cellular compartments, such as the ER, is much less well understood. Nevertheless, it is worth noting that, in the context of ATP depletion, which induces both a cytosolic and an ER stress response, selective induction of ER chaperones with tunicamycin may provide a measure of cytoprotection against cell injury and/or death.11,12 Although the mechanism of cytoprotection remains unclear, it is possible that the increased ER chaperoning capacity resulting from an ER stress response could enhance the bioassembly of proteins necessary to reassemble damaged cellular structures or specific cytoprotective cell surface proteins.12,13 Thus, because treatment with proteasome inhibitors also induces such a strong ER stress response, this type of mechanism could contribute to protection against NSAIDinduced gastropathy. This mechanism and the one suggested by the authors are not mutually exclusive. Regardless of the mechanism involved, Brand et al. provide evidence supporting the efficacy of the in vivo use of proteasome inhibitors in an animal model and justify their continued investigation in the hope of developing agents with potential clinical applicability. KEVIN T. BUSH SANJAY K. NIGAM Renal Division Department of Medicine Brigham and Women’s Hospital Harvard Medical School Boston, Massachusetts

References 1. Goldberg AL. Functions of the proteasome: the lysis at the end of the tunnel. Science 1995;268:522–523. 2. Rolfe M, Chiu MI, Pagano M. The ubiquitin-mediated proteolytic pathway as a therapeutic area. J Mol Med 1997;75:5–17. 3. Palombella VJ, Rando OJ, Goldberg AL, Maniatis T. The ubiquitinproteasome pathway is required for processing the NF-␬B1 precursor protein and the activation of NF-␬B. Cell 1994;78:773–785. 4. Brand SJ, Morise Z, Tagerud S, Mazzola L, Granger DN, Grisham MB. Role of proteasome in Rat indomethacin-induced gastropathy. Gastroenterology 1999;116:865–873. 5. Bush KT, Goldberg AL, Nigam SK. Proteasome inhibition leads to a heat-shock response, induction of endoplasmic reticulum chaperones, and thermotolerance. J Biol Chem 1997;272:9086– 9092. 6. Lee DH, Goldberg AL. Proteasome inhibitors cause induction of heat shock proteins and trehalose which together confer thermotolerance in Saccharomyces cerevisiae. Mol Cell Biol 1998;18:30–38. 7. Welch W. Mammalian stress response: cell physiology, structure/ function of stress proteins, and implications from medicine and disease. Physiol Rev 1992;72:1063–1081. 8. Gething MJ, Sambrook J. Protein folding in the cell. Nature 1992;355:33–45. 9. Nigam SK, Goldberg AL, Ho S, Rohde MF, Bush KT, Sherman M. A set of endoplasmic reticulum proteins possessing properties of molecular chaperones includes Ca(2⫹)-binding proteins and mem-

996 EDITORIALS

GASTROENTEROLOGY Vol. 116, No. 4

bers of the thioredoxin superfamily. J Biol Chem 1994;269:1744– 1749. 10. Bush KT, Hendrickson BA, Nigam SK. Induction of the FK506binding protein, FKBP13, under conditions which misfold proteins in the endoplasmic reticulum [published erratum appears in Biochem J 1995;305:1031]. Biochem J 1994;303:705–708. 11. Zhang PL, Bush KT, Nigam SK. Involvement of endoplasmic reticulum molecular chaperones (stress proteins) in recovery from epithelial ischemia (abstr). J Am Soc Nephrol 1995;6:993a. 12. Kuznetsov G, Bush K, Zhang P, Nigam S. Perturbations in maturation of secretory proteins and their association with endoplasmic reticulum chaperones in a cell culture model for

epithelial ischemia. Proc Natl Acad Sci USA 1996;93:8584– 8589. 13. Kuznetsov G, Nigam S. Defects in folding of secretory and membrane proteins in human disease. N Engl J Med 1998;339: 1688–1695. Address requests for reprints to: Sanjay K. Nigam, M.D., Renal Division, Brigham and Women’s Hospital, Harvard Institutes of Medicine, 77 Avenue Louis Pasteur, Boston, Massachusetts 02115. Fax: (617) 525-5881. r 1999 by the American Gastroenterological Association 0016-5085/99/$10.00

Sphincter of Oddi Dysfunction Type III: Another Manifestation of Visceral Hyperalgesia? See article on page 900.

phincter of Oddi dysfunction (SOD) is defined as an abnormality of sphincter of Oddi contractility that may be manifest clinically by biliary or pancreatic disorders.1,2 Along with the other functional disorders of the biliary tract, SOD forms part of the clinical spectrum of the functional gastrointestinal disorders (FGIDs).2 The most typical clinical features suggestive of SOD include recurrent episodes of severe biliary-like pain occurring after cholecystectomy, transiently elevated liver biochemistry values after episodes of pain, and perhaps a dilated common bile duct with delayed drainage at cholangiography. Two main groups of postcholecystectomy SOD are recognized clinically: patients with objective clinical criteria (so-called types I and II) and patients without objective criteria (type III).1 The technique of sphincter of Oddi manometry enables identification of those patients with manometric evidence of SOD3 and is regarded as the most definite investigation compared with noninvasive procedures such as biliary scintigraphy. Patients with SOD type II display abnormal sphincter of Oddi manometry in approximately 50% of cases; the prevalence of elevated basal sphincter pressure in type III patients appears to be between 12% and 55%.4 The elevated basal sphincter pressure seems to respond to endoscopic sphincterotomy in patients with SOD type II,5 but the response in type III patients is less established. Botoman et al.,4 however, showed that type III patients with elevated basal pressure respond as well to endoscopic sphincterotomy as type II patients.

S

In this issue of GASTROENTEROLOGY, the report by Desautels et al.6 represents a further step toward documentation of pathophysiological factors common to both the functional biliary tract disorders and the FGIDs. These investigators used the current gold standard methodology of the electronic barostat7 to assess gastrointestinal tract (duodenal and rectal) sensitivity in patients with SOD type III. The main findings were that (1) patients within this specific category of SOD exhibited duodenal (but not rectal) hyperalgesia, despite the presence of normal intestinal compliance; (2) duodenal distention reproduced the characteristic symptoms in all but 1 patient; and (3) the patients demonstrated high levels of somatization, depression, obsessive and compulsive behavior, and anxiety compared with controls, but these levels did not correlate with the alterations in duodenal pain sensitivity. Before discussing the implications of these findings, several aspects of the study design warrant comment. First, only 2 of the control group subjects had undergone cholecystectomy, and in the absence of an additional control group of asymptomatic cholecystectomized subjects, an effect of cholecystectomy per se on duodenal sensitivity cannot be excluded. Second, a comparison group of patients with SOD type II would have been ideal because, based on the data presented, it is not possible to conclude that duodenal hypersensitivity is present in SOD type III patients only. Thus, if the same phenomenon was true for SOD type II patients, it would weaken the proposition that symptoms in SOD type III are generated by different mechanisms than in type II patients, arising from the duodenum rather than from the