Complement activation correlates with liver necrosis and fibrosis in chronic hepatitis C.

Chronic hepatitis C viral infection modulates complement. The aim of this study was to determine whether complement analysis predicts liver inflammation and fibrosis in patients with chronic hepatitis C. 50 chronic hepatitis C patients who underwent a liver biopsy were compared to 50 healthy controls and 35 patients with various liver diseases. Total plasma complement activity (CH50) in plasma was diminished in hepatitis C patients suggesting complement activation. This decrease correlated with increased necrosis (r = -0.24, p < 0.05), and patients with levels below the normal range had a higher METAVIR activity score reflecting enhanced inflammation. SC5b-9, a marker of complement activation, correlated with inflammation (r = 0.40, p < 0.05), activity (r = 0.42, p < 0.05), and fibrosis scores (r = 0.49, p < 0.05). Finally, the prevalence of C1q auto-antibodies was higher in hepatitis C patients, and their presence was associated with increased inflammation and seemed to affect fibrosis. We conclude that complement-induced liver inflammation contributes to fibrosis in patients with chronic hepatitis C.

Hepcidin is localised in gastric parietal cells, regulates acid secretion and is induced by Helicobacter pylori infection.

BACKGROUNDS AND AIMS: Hepcidin is an antimicrobial peptide and the central regulator of iron metabolism. Given that hepcidin was shown to be expressed in a variety of extrahepatic tissues and that stomach plays a role in iron absorption and in defence against infections, this study analysed the importance of hepcidin in the stomach. METHODS: Expression and localisation of gastric hepcidin was studied by quantitative RT-PCR, western blot, immunofluorescence and in situ hybridisation. Regulation of gastric hepcidin expression was analysed both in vitro and in vivo. Hepcidin wild-type (WT) and knockout (KO) animals were used to determine the impact of hepcidin on gastric bacterial overgrowth as well as gastric acid secretion. RESULTS: Hepcidin was abundantly expressed in the gastric fundus and corpus of all tested species. Treatment of AGS cells with ferric nitrilotriacetate solution downregulated hepcidin expression levels, while desferroxamine, interleukin 6 and Helicobacter pylori infection upregulated it. In humans, gastric hepcidin expression was elevated during H pylori infection and normalised after successful eradication. Gastric hepcidin is localised in parietal cells that are indispensable for gastric acid secretion. Comparisons of WT and hepcidin KO mice revealed that acid secretion in hepcidin-deficient mice is markedly reduced and is associated with gastric bacterial overgrowth, expression changes in multiple factors involved in acid secretion (Atp4a, Cck2r,Gas, Sst and Sst2r) and with reduced circulating gastrin levels. In WT mice, pantoprazole activated and histamine downregulated hepcidin expression levels. CONCLUSIONS: Hepcidin is a product of parietal cells regulating gastric acid production and may contribute to development of gastric ulcers under stress conditions.

Alcohol and smoking.

The WHO ranks smoking and alcohol consumption as the first and third leading causes of the global burden of disease in industrialized countries, using disability-adjusted life years (DALYs) as a combined measure of premature death and disability. Smoking is responsible for 12.2% of all DALYs and alcohol consumption for 9.2%. For example in Germany, annually 110,000-140,000 humans die prematurely because of cigarette smoking and 40,000 because of alcohol drinking. In Europe and the USA, more than 20% of all hospitalized men and more than 9% of all hospitalized women suffer from alcohol-associated diseases. In Germany, about 2.0 million people in the age group 18-64 years (3.8% of all Germans) are alcohol abusers and 1.3 million people (2.4%) are alcohol-dependent. Alcohol can cause acute as well as chronic damage in nearly all body organs. Smoking damages also nearly every human body organ and is worldwide the most important single preventable health risk factor as well as the main cause for premature mortality in industrial countries. One third of the adult Germans as well as of the world population are active smokers; men smoke more frequently than women (34.0 vs. 25.1%). In this review a short overview will be given on the most important deleterious effects of alcohol and smoking. The most recent data about the pathophysiological relevance of non-alcoholic compounds of alcoholic beverages will also be discussed.

Circulating fibronectin isoforms predict the degree of fibrosis in chronic hepatitis C.

OBJECTIVE: Hepatic stellate cells only produce fibronectin isoforms in disease states. The isoform-defining domains can be detected in the blood circulation. This study examines whether circulating levels of fibronectin isoforms show a relationship with liver fibrosis on histology in patients with chronic hepatitis C. MATERIAL AND METHODS: In a prospective study, 50 patients with chronic hepatitis C who underwent a liver biopsy were compared to 50 matched controls and 35 patients with other liver conditions. RESULTS: Circulating levels of the fibronectin isoforms were significantly higher in patients with chronic hepatitis C compared to healthy controls [oncofetal fibronectin (oFN) 2.45 +/- 0.17 versus 1.76 +/- 0.16 mg/l, P < 0.005; extra domain-A (EDA) 1.05 +/- 0.06 versus 0.86 +/- 0.06 mg/l, P < 0.05; and extra domain-B (EDB) 14.55 +/- 0.74 versus 9.31 +/- 0.58 mg/l, P < 0.001], even though total fibronectin was lower (198.9 +/- 3.5 versus 343.6 +/- 14.5 mg/l, P < 0.001). A correlation with the fibrosis score was found for both oFN (r = 0.46, P < 0.005) and EDA (r = 0.51, P < 0.001). The combination of an elevation in both markers (oFN and EDA) in the upper quartile was associated with a specificity of > 99% for predicting significant fibrosis (stages 2-4) and 95% for predicting advanced fibrosis (stages 3-4). A combination of decreased values in the lowest tertile for both markers had a specificity of 94% for excluding significant fibrosis. Based on these findings, 30% of the patients scheduled for a liver biopsy could be correctly classified as having or not having significant fibrosis. The remainder would have to proceed with a biopsy. CONCLUSION: Circulating fibronectin isoforms produced by activated stellate cells represent a viable marker for the presence of significant fibrosis or a lack thereof.

Pancreas - non-alcoholic constituents and their effects.

Alcoholic beverages contain numerous non-alcoholic compounds that could have beneficial or pathological effects. For example, up to now in beer more than 2,000 and in wine more than 1,000 organic and inorganic constituents have been identified. Whereas the role of alcohol (ethanol) in the development of pancreatic diseases - in particular acute and chronic pancreatitis - has been intensively investigated, only little is known about the effects of non-alcoholic compounds in this context. Some of the non-alcoholic constituents have been shown to be biologically active, although discussions of the results in appropriate publications were often not performed with regard to their consumption as a mixture in alcoholic beverages. In this article we provide an overview about the newest data concerning the effect of non-alcoholic constituents of alcoholic beverages, especially of beer, on pancreatic secretion and their possible role in alcoholic pancreatitis. The data indicate that non-alcoholic constituents of beer stimulate pancreatic enzyme secretion in humans and rats, at least in part, by direct action on pancreatic acinar cells. However, there is accumulating evidence that non-alcoholic compounds of alcoholic beverages exert different effects on the pancreas. The effects and mechanisms of most single compounds and their combinations are still unknown and thus caution is required in attempting to draw firm conclusions on the effect of non-alcoholic compounds of alcoholic beverages on defining alcoholic etiology of pancreatitis.

Beer but not wine, hard liquors, or pure ethanol stimulates amylase secretion of rat pancreatic acinar cells in vitro.

BACKGROUND: In contrast to pure ethanol, the effect of alcoholic beverages on the exocrine pancreas is greatly unknown. Besides ethanol, alcoholic beverages contain numerous nonalcoholic constituents which might have pathophysiological effects on the pancreas. The aim of the present study was to investigate whether some commonly used alcoholic beverages and pure ethanol influence the main function of rat pancreatic acinar cells, i.e., enzyme output in vitro. METHODS: Rat pancreatic AR4-2J cells were differentiated by dexamethasone treatment for 72 hours and freshly isolated pancreatic acini were prepared from Sprague-Dawley rats using collagenase digestion. After incubation of cells in the absence or presence of 1 to 10% (v/v) beer (containing 4.7% v/v ethanol), 10% (v/v) wine (containing 10.5 to 12.5% v/v ethanol), 10% (v/v) hard liquor (such as whisky, rum, and gin), or of the corresponding ethanol concentrations (4.03 to 80.6 mM) for 60 minutes, protein secretion was measured using amylase activity assay. RESULTS: Incubation of AR4-2J cells with beer caused a dose-dependent stimulation of basal amylase secretion that was significant at doses of beer above 0.5% (v/v). Stimulation with 10% (v/v) beer induced 92.7 +/- 25.2% of maximal amylase release in response to the most effective cholecystokinin (CCK) concentration (100 nM). In contrast, ethanol (up to 80.6 mM) did neither stimulate nor inhibit basal amylase release. Lactate dehydrogenase measurement after treatment of AR4-2J cells with beer for 24 hours indicated that the increase of amylase release was not due to cell membrane damage. Wine and hard liquor had no effect on basal amylase secretion neither diluted to the ethanol concentration of beer nor undiluted. In freshly isolated rat pancreatic acinar cells beer dose-dependently stimulated amylase secretion in a similar manner as in AR4-2J cells. CONCLUSIONS: Our data demonstrate that beer dose-dependently increases amylase output. Since neither ethanol nor the other alcoholic beverages tested caused stimulation of amylase release, our findings indicate that nonalcoholic constituents specific for beer are responsible for this increase. These as yet unknown compounds have to be identified and considered in further studies of ethanol-induced pathological and functional changes of the pancreas.

Beer-induced pancreatic enzyme secretion: characterization of some signaling pathways and of the responsible nonalcoholic compounds.

BACKGROUND: Various alcoholic beverages have different effects on pancreatic enzyme secretion in vivo and in vitro. Recently we demonstrated that beer dose-dependently induces amylase release of rat pancreatic acinar cells, whereas pure ethanol and other alcoholic beverages have no effect. The aims of this study were to: (1) investigate the involved signaling pathways in the beer-induced enzyme secretion of rat pancreatic acinar cells and (2) characterize the responsible nonalcoholic compounds from beer. METHODS: Rat pancreatic AR4-2J cells were differentiated by dexamethasone treatment for 72 hours. After incubation of cells with 1 to 10% (v/v) beer (containing 4.7% v/v ethanol) in the absence or presence of the maximal effective concentration of cholecystokinin (CCK) (100 nM) for 60 minutes, protein secretion was measured using amylase activity assay. To study the involved signaling pathways, cells were pretreated with selective inhibitors or the fluorescent dye Fura2/AM for 15 and 30 minutes, respectively. To characterize the responsible compounds, beer was distilled, lyophilized, dialyzed, or treated with proteases prior stimulation of the cells. Extract of barley was prepared by boiling the crop and subsequent filtration. RESULTS: Stimulation with 5% and 10% beer (v/v) significantly (p < 0.001) increased maximally CCK-induced amylase by 55 +/- 25% and 56 +/- 37%, respectively. By using selective antagonists, we found that inhibition of phospholipase C (PLC) and inositol 1,4,5-trisphosphate-receptor binding reduced beer-induced amylase release, whereas inhibition of protein kinase C, adenylate cyclase, and protein kinase A had no significant effect. Using the fluorescent Ca(2+) indicator Fura-2/AM revealed that beer induces an increase of cytosolic free Ca(2+) concentration. Stimulation of AR4-2J cells with preproducts of beer and fermented glucose indicated that the stimulatory substances from beer derived from barley and are not produced during alcoholic fermentation. Furthermore, the stimulants from beer are thermostable, nonvolatile substances with a molecular weight higher than 15 kDa. CONCLUSIONS: Beer-induced enzyme secretion of AR4-2J cells is, at least in part, mediated by the activation of PLC and subsequent Ca(2+) release from internal stores. However, the additive effect of beer on CCK-induced amylase release suggests that additional signaling pathways are involved. The yet unknown stimulants of pancreatic enzyme secretion originate from barley and their stimulatory potential is maintained during the process of malting and brewing.

The biological responses to resveratrol and other polyphenols from alcoholic beverages.

Although excessive consumption of ethanol in alcoholic beverages causes multi-organ damage, moderate consumption, particularly of red wine, is protective against all-cause mortality. These protective effects could be due to one or many components of the complex mixture of bioactive compounds present in red wine including flavonols, monomeric and polymeric flavan-3-ols, highly colored anthocyanins as well as phenolic acids and the stilbene polyphenol, resveratrol. The therapeutic potential of resveratrol, firstly in cancer chemoprevention and then later for cardioprotection, has stimulated many studies on the possible mechanisms of action. Further indications for resveratrol have been developed, including the prevention of age-related disorders such as neurodegenerative diseases, inflammation, diabetes, and cardiovascular disease. These improvements are remarkably similar yet there is an important dichotomy: low doses improve cell survival as in cardio- and neuro-protection yet high doses increase cell death as in cancer treatment. Fewer studies have examined the responses to other components of red wine, but the results have, in general, been similar to resveratrol. If the nonalcoholic constitutents of red wine are to become therapeutic agents, their ability to get to the sites of action needs to be understood. This mini-review summarizes recent studies on the possible mechanisms of action, potential therapeutic uses, and bioavailability of the nonalcoholic constituents of alcoholic beverages, in particular resveratrol and other polyphenols.

Low-dose exposure of intestinal epithelial cells to formaldehyde results in MAP kinase activation and molecular alteration of the focal adhesion protein paxillin.

We investigated the potential pathophysiological role of non-lethal formaldehyde concentrations on human intestinal epithelial HT-29 cells. Expression levels of actin, tubulin and detectable cytokeratin isoforms 5, 13, 18, 19 and 20 were not affected after 24h of exposure to 1mM formaldehyde. By contrast, cellular organization of cytoskeletal constituents was already changed after 60 min. Within 15 min, formaldehyde induced profound tyrosine phosphorylation of the focal adhesion protein paxillin and of proteins at about 120-130 kDa. Concomitantly, phosphorylation of ERK-1/2 and p38 MAP kinase occurred. Paxillin was not only tyrosine phosphorylated but underwent a sustained molecular weight shift representing serine/threonine phosphorylation that was independent of MAP kinase activity and EGF-R-mediated signalling. Our data show that exposure of intestinal epithelial cells to low-dose formaldehyde is followed by rapid and profound signalling events. The data suggest a modifier role of environmental or endogenous formaldehyde for epithelial cell functions.

Enhanced expression of interleukin-18 in serum and pancreas of patients with chronic pancreatitis.

AIM: To investigate interleukin-18 (IL-18) in patients with chronic panreatitis (CP). METHODS: We studied 29 patients with CP and 30 healthy controls. Peripheral blood mononuclear cells (PBMC) were isolated and incubated with 50 mmol/L ethanol, lipopolysaccharide (LPS) (doses 25 g/L, 250 g/L, 2500 g/L) and both agents for 24 h. Levels of IL-18 in the supernatants, and levels of IL-18, IL-12, interferon (IFN)-gamma and soluble CD14 in the serum were analysed by ELISA technique. Expression of IL-18 in PBMC was investigated by reverse-transcription (RT)-PCR. IL-18 protein levels in CP tissue and in normal pancreas were studied by ELISA technique. IL-18 levels in PBMC and pancreatic tissue were determined by Western blot. Immunohistochemistry for pancreatic IL-18 expression was performed. RESULTS: In patients, IL-18 serum levels were significantly enhanced by 76% (mean: 289.9+/-167.7 ng/L) compared with controls (mean: 165.2+/-43.6 ng/L; P<0.0005). IL-12 levels were enhanced by 25% in patients (18.3+/-7.3 ng/L) compared with controls (14.7+/-6.8 ng/L, P=0.0576) although not reaching the statistical significance. IFN-gamma and soluble CD14 levels were not increased. In vitro, LPS stimulated significantly and dose-dependently IL-18 secretion from PBMC. Incubation with ethanol reduced LPS-stimulated IL-18 secretion by about 50%. The mRNA expression of IL-18 in PBMC and the response of PBMC to ethanol and LPS was similar in CP patients and controls. In PBMC, no significant differences in IL-18 protein levels were detected between patients and controls. IL-18 protein levels were increased in CP tissues compared to normal pancreatic tissues. IL-18 was expressed by pancreatic acinar cells and by infiltrating inflammatory cells within the pancreas. CONCLUSION: IL-18 originates from the chronically inflammed pancreas and appears to be involved in the fibrotic destruction of the organ.

Expression of IL-18 in patients with head and neck squamous cell carcinoma.

Interleukin-18 (IL-18), a recently described cytokine secreted mainly by macrophages, stimulates interferon-gamma (IFN-gamma) production by natural killer cells and T cells. The purpose of this study was to determine tissue expression and serum levels of IL-18 in head and neck squamous cell carcinoma (HNSCC) and to evaluate ethanol and endotoxin-driven cytokine secretion. In 24 patients with primary HNSCC and 28 healthy controls, PBMC were isolated and incubated with 50 mM ethanol, LPS (doses 25 ng/ml, 250 ng/ml, 2500 ng/ml) and both agents for 24 h. Levels of IL-18 in serum, and cell supernatants were analysed by capture ELISA, IL-18 tissue level by immunoblotting. Serum levels of IL-8, IL-10 and IL-12, IFN-gamma, and endotoxin plasma levels were also determined. Statistical analysis involved Welch t-test and Page's test for trend. The majority of patients with HNSCC had high concentrations of serum IL-18. The level of IL-18 in the sera of these patients had a mean level of 271.7 pg/ml, while the mean IL-18 serum level in healthy controls was 174,0 pg/ml (p<0.001). Levels of IL-10 and IL-12, IFN-gamma were not increased in patients. Endotoxin was not detectable in either group. LPS stimulated dose-dependently IL-18 secretion from PBMC of patients and controls in vitro (p<0.05). Incubation with ethanol alone did not affect basal IL-18 secretion, but ethanol reduced LPS-stimulated IL-18 secretion compared to LPS stimulation alone. The mRNA expression of IL-18 in unstimulated PBMC and the response of PBMC to ethanol and LPS was similar in patients and controls. Our data on elevated serum levels of IL-18 in the majority of HNSCC cancer patients, irrespective of its biological activity, suggest that serum IL-18 might be a candidate for a new marker for HNSCC. The pathways for IL-18 production and its mechanisms of action in patients with HNSCC remain to be determined. Understanding of the immunological pathways might offer new therapeutic options in head and neck cancer in the future.

Beer and its non-alcoholic compounds: role in pancreatic exocrine secretion, alcoholic pancreatitis and pancreatic carcinoma.

In this article we provide an overview of the newest data concerning the effect of non-alcoholic constituents of alcoholic beverages, especially of beer, on pancreatic secretion, and their possible role in alcoholic pancreatitis and pancreatic carcinoma. The data indicate that non-alcoholic constituents of beer stimulate pancreatic enzyme secretion in humans and rats, at least in part, by direct action on pancreatic acinar cells. Some non-alcoholic compounds of beer, such as quercetin, resveratrol, ellagic acid or catechins, have been shown to be protective against experimentally induced pancreatitis by inhibiting pancreatic secretion, stellate cell activation or by reducing oxidative stress. Quercetin, ellagic acid and resveratrol also show anti-carcinogenic potential in vitro and in vivo. However, beer contains many more non-alcoholic ingredients. Their relevance in beer-induced functional alterations of pancreatic cells leading to pancreatitis and pancreatic cancer in humans needs to be further evaluated.

Isoform of fibronectin mediates bone loss in patients with primary biliary cirrhosis by suppressing bone formation.

Osteoporosis is a major cause of morbidity and decreased quality of life in patients with chronic cholestatic liver disease. It is established that this osteoporosis results from decreased bone formation, but the mechanisms for the interaction between liver and bone remain elusive. The aim of this study was to test the hypothesis that an increase in the production of cellular fibronectins during liver disease may result in decreased osteoblast-mediated mineralization and thus explain the decrease in bone formation. We performed a prospective cross-sectional study in patients with primary biliary cirrhosis and matched controls, followed by experiments on human and mouse osteoblasts in culture and injections in mice in vivo. In patients with primary biliary cirrhosis, the oncofetal domain of fibronectin correlated significantly with the decrease in osteocalcin, a marker of bone formation (r = -0.57, p < 0.05). In vitro, amniotic fluid fibronectin (aFN) containing mainly the oncofetal domain and EIIIA domain resulted in decreased osteoblast-mediated mineralization in human osteoblasts (69% decrease at 100 microg/ml; p < 0.01) and mouse osteoblasts (71% decrease; p < 0.05). Removing the EIIIA domain from aFN similarly suppressed mineralization by osteoblasts (78% decrease; p < 0.05). Injection of labeled aFN in mice showed that it infiltrates the bone, and its administration over 10 days resulted in decreased trabecular BMD (17% drop; p < 0.05), mineralizing surface (30% drop; p < 0.005), and number of osteoblasts (45% drop; p < 0.05). Increased production of a fibronectin isoform containing the oncofetal domain and its release in the circulation in patients with primary biliary cirrhosis is at least partially responsible for the decrease in bone formation seen in these patients. This establishes that a molecule that has thus far been viewed as an extracellular matrix protein exerts hormone-like actions.

Effect of non-alcoholic compounds of alcoholic drinks on the pancreas.

Over the past 30 years the role of alcohol (ethanol) in the development of acute and chronic pancreatitis has been intensively investigated. However, ethanol is generally consumed in form of alcoholic beverages which contain numerous non-alcoholic compounds. At least on gastric acid secretion it has been convincingly demonstrated that alcohol and alcoholic beverages have markedly different effects. In the present article, we provide an overview about the effect of different non-alcoholic constituents of alcoholic beverages on the pancreas and their possible interaction with molecular mechanisms leading to 'alcoholic' pancreatitis. The present data indicate that pancreatic enzyme secretion in humans is stimulated by non-alcoholic constituents of beer which are generated by alcoholic fermentation of glucose. In addition, it has been shown that natural phenolic compounds (e.g. quercetin, resveratrol) of alcoholic beverages exert different effects on the pancreasin vitro, such as inhibition of pancreatic enzyme output, of pancreatic stellate cell activation and of pancreatic cancer growth as well as protective effects against oxidative stress and on experimental induced acute pancreatitis in rats. However, it should be pointed out that alcoholic beverages contain much more non-alcoholic ingredients. Since the effects of these are still unknown, caution is required in attempting to define alcoholic etiology of pancreatitis without considering the effect of non-alcoholic compounds of alcoholic beverages.

Responsiveness of intestinal epithelial cell lines to lipopolysaccharide is correlated with Toll-like receptor 4 but not Toll-like receptor 2 or CD14 expression.

BACKGROUND AND AIMS: Luminal bacteria have been implicated in the pathogenesis of inflammatory bowel diseases. Exposure of intestinal epithelial cells (IEC) to bacterial components potentially initiates intestinal inflammation by release of chemokines and recruitment of inflammatory cells. We analyzed receptor expression and signaling pathways involved in activation of human primary IEC and carcinoma-derived cell lines by lipopolysaccharide (LPS). MATERIALS AND METHODS: HT-29/p, HT-29/MTX, and Caco-2 cells were stimulated by LPS. IL-8 content in supernatants was analyzed by ELISA, and expression of CD14, Toll-like receptor (TLR) 2 and TLR 4 was determined by RT-PCR. Presence of TLR 4 protein was assessed by western blot analysis. LPS response was modulated by sCD14, LPS-binding protein, neutralization of CD14, and inhibitors of early signal activation. RESULTS: LPS dose-dependently induced secretion of IL-8 in undifferentiated HT-29/p cells while Caco-2 and permanently differentiated HT-29/MTX cells were unresponsive. Differently to HT-29/MTX, both HT-29/p and Caco-2 cells constitutively expressed transcripts for CD14. However, CD14 was not required for LPS-mediated induction of IL-8 in HT-29/p cells since neutralizing anti-CD14 antibodies left IL-8 levels unchanged. Unresponsiveness of Caco-2 and HT-29/MTX cells to LPS persisted in the presence of sCD14 and/or LPS-binding protein. Neither cell line expressed TLR 2 transcripts while only responsive HT-29/p cells expressed TLR 4 mRNA and TLR 4 protein. Butyrate down-regulated TLR 4 expression and significantly diminished LPS-dependent IL-8 secretion. Inhibition of G protein dependent kinase activation reduced IL-8 levels to 50%; the phosphatidyl-inositol-3'-kinase inhibitor LY294002 abrogated the response. CONCLUSION: Responsiveness of IEC lines to LPS is positively correlated with TLR 4 expression. Strategies targeting TLR 4 expression or TLR 4 mediated signaling may antagonize IEC activation by LPS.

A novel type of co-chaperone mediates transmembrane recruitment of DnaK-like chaperones to ribosomes.

Recently, the homolog of yeast protein Sec63p was identified in dog pancreas microsomes. This pancreatic DnaJ-like protein was shown to be an abundant protein, interacting with both the Sec61p complex and lumenal DnaK-like proteins, such as BiP. The pancreatic endoplasmic reticulum contains a second DnaJ-like membrane protein, which had been termed Mtj1p in mouse. Mtj1p is present in pancreatic microsomes at a lower concentration than Sec63p but has a higher affinity for BiP. In addition to a lumenal J-domain, Mtj1p contains a single transmembrane domain and a cytosolic domain which is in close contact with translating ribosomes and appears to have the ability to modulate translation. The interaction with ribosomes involves a highly charged region within the cytosolic domain of Mtj1p. We propose that Mtj1p represents a novel type of co-chaperone, mediating transmembrane recruitment of DnaK-like chaperones to ribosomes and, possibly, transmembrane signaling between ribosomes and DnaK-like chaperones of the endoplasmic reticulum.