Increased interleukin-6/C-reactive protein levels are associated with the upregulation of the adenosine pathway and serve as potential markers of therapeutic resistance to immune checkpoint inhibitor-based therapies in non-small cell lung cancer

BACKGROUND

Systemic immune activation, hallmarked by C-reactive protein (CRP) and interleukin-6 (IL-6), can modulate antitumor immune responses. In this study, we evaluated the role of IL-6 and CRP in the stratification of patients with non-small cell lung cancer (NSCLC) treated with immune checkpoint inhibitors (ICIs). We also interrogated the underlying immunosuppressive mechanisms driven by the IL-6/CRP axis.

METHODS

In cohort A (n=308), we estimated the association of baseline CRP with objective response rate (ORR), progression-free survival (PFS), and overall survival (OS) in patients with NSCLC treated with ICIs alone or with chemo-immunotherapy (Chemo-ICI). Baseline tumor bulk RNA sequencing (RNA-seq) of lung adenocarcinomas (LUADs) treated with pembrolizumab (cohort B, n=59) was used to evaluate differential expression of purine metabolism, as well as correlate IL-6 expression with PFS. CODEFACS approach was applied to deconvolve cohort B to characterize the tumor microenvironment by reconstructing the cell-type-specific transcriptome from bulk expression. Using the LUAD cohort from The Cancer Genome Atlas (TCGA) we explored the correlation between IL-6 expression and adenosine gene signatures. In a third cohort (cohort C, n=18), plasma concentrations of CRP, adenosine 2a receptor (A2aR), and IL-6 were measured using ELISA.

RESULTS

In cohort A, 67.2% of patients had a baseline CRP≥10 mg/L (CRP-H). Patients with CRP-H achieved shorter OS (8.6 vs 14.8 months; p=0.006), shorter PFS (3.3 vs 6.6 months; p=0.013), and lower ORR (24.7% vs 46.3%; p=0.015). After adjusting for relevant clinical variables, CRP-H was confirmed as an independent predictor of increased risk of death (HR 1.51, 95% CI: 1.09 to 2.11) and lower probability of achieving disease response (OR 0.34, 95% CI: 0.13 to 0.89). In cohort B, RNA-seq analysis demonstrated higher IL-6 expression on tumor cells of non-responders, along with a shorter PFS (p<0.05) and enrichment of the purinergic pathway. Within the TCGA LUAD cohort, tumor IL-6 expression strongly correlated with the adenosine signature (R=0.65; p<2.2e-16). Plasma analysis in cohort C demonstrated that CRP-H patients had a greater median baseline level of A2aR (6.0 ng/mL vs 1.3 ng/mL; p=0.01).

CONCLUSIONS

This study demonstrates CRP as a readily available blood-based prognostic biomarker in ICI-treated NSCLC. Additionally, we elucidate a potential link of the CRP/IL-6 axis with the immunosuppressive adenosine signature pathway that could drive inferior outcomes to ICIs in NSCLC and also offer novel therapeutic avenues.

Low Protein Intake Irrespective of Source is Associated with Higher Mortality Among Older Community-dwelling Men

OBJECTIVES

Our aim was to determine the association between protein intake (overall and by source) and all-cause and cause-specific mortality among older men.

DESIGN

Prospective cohort study.

SETTING

5790 ambulatory community-dwelling older men from multicenter Osteoporotic Fractures in Men (MrOS) study.

MEASUREMENTS

Total energy and protein intake, and protein intake by source (dairy, non-dairy animal, plant) were assessed using a 69-item food frequency questionnaire. We included up to 10-year follow-up with adjudicated cardiovascular, cancer and other mortality outcomes. We used time-to-event analysis with protein exposures, mortality outcome, and adjusted for possible confounders including age, center, education, race, smoking, alcohol use, physical activity, weight, total energy intake (TEI), and comorbidities. Hazard ratios were expressed per each unit=2.9% TEI decrement for all protein intake variables.

RESULTS

The mean (SD) baseline age of 5790 men was 73.6 (5.8) y. There were 1611 deaths and 211 drop-outs prior to 10 years, and 3868 men who were alive at the 10-year follow-up. The mean (SD) total protein intake was 64.7 (25.8) g/d, while the mean (SD) intake expressed as percent of total energy intake (%TEI) was 16.1 (2.9) %TEI. Lower protein intake was associated with an increased risk of death, with unadjusted HR=1.11 (95% CI: 1.06, 1.17) and adjusted HR=1.09 (95% CI: 1.04, 1.14) and the associations for protein intake by source were similar. The adjusted HR for cancer mortality was HR=1.13 (95% CI: 1.03, 1.25) while the association for CVD mortality was HR=1.08 (95% CI: 0.99, 1.18).

CONCLUSIONS

Low protein intake, irrespective of source, was associated with a modest increase in risk of all-cause and cause-specific mortality among older men. Special consideration should be given to level of protein intake among older adults.

SIDE in metastatic colon cancer: SEER Database analysis

753

Background: Recent data suggests side of colon cancer is a prognostic factor and a potential predictive factor for biologic therapy. We sought to analyze SEER database to study impact of colon cancer side. Methods: The SEER database (version 8.3.4) was reviewed for patients with Stage IV colon cancer from 2004-2014. We only included patients with labeled primary site, and excluded appendiceal, rectal or unlabeled cases. Variables included were: age, race, gender, stage, grade and side of the tumor. Primary outcome was overall survival and disease specific survival. Cox proportional hazard regression model was employed to test the association between survival and side of cancer. Results: 48,306 patients met the inclusion criteria, median age was 67 years (range 20-108), 51% were male, and 77% patients were white. 19831 (41%) patients had left colon cancer (LCC). Right colon cancer (RCC) was associated with inferior OS and DSS compared to LCC. The median overall survival was 15 months (mo) for left side and 9 months for right colon cancer (p<0.0001). Estimated 3-year OS for RCC was 14% and 24% for LCC (p <0.0001). RCC was associated with poor outcome across different variables, among patients < 60 years of age median OS was 23 mo for LCC, and 16 mo for RCC (p .0001). In the age group ≥ 60 years, 10 mo for left side and 7 mo for RCC (p < 0.0001). Among male patients RCC had 10 mo median OS vs 16 mo for LCC (p <0.0001), women 15mo for LCC vs 9mo for RCC (<0.0001). Cox regression model suggested age (<0.001), race (<0.0001), year of diagnosis (<0.0001) and grade (<0.0001) correlate with outcome. Conclusions: Right side colon cancer is associated with poor outcome compared to left colon cancer. These findings are consistent with other recent reports.

Equality during end-of-life cancer care: Trends in aggressiveness of cancer care at the end of life

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Background: Aggressive cancer care at the end of life (EOL) can impact quality of life and have major economic burden. The purpose of this study was to portray the aggressiveness of EOL cancer care, and its relation to race, gender and social factors in Eastern North Carolina with high rural and minority population. Methods: This is a retrospective analysis of 401 stage 4 solid tumor patients who died between 2011 and 2014. Aggressiveness of care was calculated by a composite score adopted from Earle et al. Scores range from 0 to 7 with higher scores indicating more aggressive EOL care. 1 point was given to each indicator of aggressiveness in the last 30 days of life: ED visits ≥2,hospital admissions ≥2,any ICU admission,hospitalized days ≥14,new chemotherapy, hospice care ≤ 3 days, and any chemotherapy in the last 14 days. Results: Among the 401 patients, 217 (54%) were white and 178 (44%) were black. The mean composite score of aggressiveness (CSA) for whites was 1.18 and for blacks it was 1.87. (p<0.001).In the last 30 days of death, a higher proportion of blacks had ≥ 2 ED visits 28% vs 13%(p<.0001), ≥ 2 hospital admission 23% vs 13%(p=0.001), any ICU admission 29% vs 16%(p=0.0002), chemotherapy in the last 14 days 30% vs 20%(p=0.001), ≥ 14 hospitalized days 35% vs 21%(p<0.001), and hospital deaths 46% vs 32%(p=0.001) compared to whites. More whites enrolled in hospice compared to blacks 53% vs 45% (p<0.001). Correlation analysis using Fit Y by X model between CSA (score ≤ 3 and >3) and other variables showed statistically significant difference between whites vs blacks p <0.001, females vs males p=0.0006, not married vs married p<0.0001, and no family support vs family support p<0.0001. Conclusions: Male, unmarried and black patients were associated with higher CSA. Patients who were white, married and with family support had high likelihood of enrolling in hospice. [Table: see text]

Incidence and correlates of tuberculosis IGRA conversion among HIV-infected postpartum women

SETTING

Prevention of maternal-to-child transmission program at a tertiary care hospital in Nairobi, Kenya. The risk of acquiring Mycobacterium tuberculosis infection among peripartum human immunodeficiency virus (HIV) infected women is poorly defined.

OBJECTIVE

To determine the incidence of and co-factors for interferon-gamma release assay (IGRA) conversion among postpartum HIV-infected women using T-SPOT.TB.

DESIGN

We used data and cryopreserved peripheral blood mononuclear cells from a historical cohort of HIV-infected women enrolled at 32 weeks' gestation and followed for 1 year postpartum between 1999 and 2005.

RESULTS

Of 89 women initially IGRA-negative during pregnancy, 11 (12.4%) became positive, 53 (59.5%) remained negative and 25 (28.1%) were indeterminate at 1 year postpartum. Mean interferon-gamma (IFN-γ) response among converters increased from ~1 to >50 spot-forming cells/well (P = 0.015). IGRA conversion was significantly associated with partner HIV infection, flush toilets, maternal illness and cough during follow-up, but not maternal CD4 count or HIV viral load.

CONCLUSION

The high rates of IGRA conversion seen among HIV-infected postpartum women in our study are similar to those of other groups at high risk for M. tuberculosis infection. This has important implications for M. tuberculosis infection screening strategies and provision of preventive therapy for the health of women and their infants.

Prognostic Performance of Current Stage III Oral Cancer Patients After Curative Intent Resection: Evidence to Support a Revision of the American Joint Committee on Cancer Staging System

BACKGROUND

The American Joint Committee on Cancer (AJCC) stage III classification of oral cavity squamous cell carcinoma (OCSCC) represents a heterogeneous group of patients with early local disease with regional metastases (T1N1 and T2N1) and advanced local disease with or without regional metastasis (T3N0 and T3N1).

OBJECTIVE

The aim of this study was to evaluate prognostic heterogeneity in the stage III category.

METHODS AND PATIENTS

An international retrospective multicenter study of 1815 patients who were treated for OCSCC from 2003 to 2011.

RESULTS

Kaplan-Meier survival analysis and multivariate models of stage III patients revealed better overall survival (OS; HR 2.12, 95 % CI 1.03-4.15; p = 0.01) and disease-specific survival (DSS; HR 1.7, 95 % CI 1.16-4.12; p = 0.04) rates for patients with T1-2N1/T3N0 disease than for patients with T3N1 disease. The outcomes of patients with T3N1 and stage IVa disease were similar (p = 0.89 and p = 0.78 for OS and DSS, respectively). Modifying stage classification by transferring the T3N1 category to the stage VIa group resulted in a better prognostic performance [Harrell's concordance index, C index 0.76; Akaike's Information Criterion (AIC) 4131.6] compared with the AJCC 7th edition staging system (C index 0.65; AIC 4144.9) for OS. When DSS was assessed, the suggested staging system remained the best performing model (C index 0.71; AIC 1061.3) compared with the current AJCC 7th edition staging (C index 0.64; AIC 1066.2).

CONCLUSIONS

The prognosis of T3N1 and stage IVa disease are similar in OCSCC, suggesting that these categories could be combined in future revisions of the nodal staging system to enhance prognostic accuracy.

The effect of coencapsulation of bovine insulin with cyclodextrins in ethylcellulose microcapsules

Polymeric microcapsules have been widely investigated for protein delivery. Common problems include: low stability, low encapsulation efficiency, lack of uniformity, and burst release. Cyclodextrins (CDs) are known to enhance stability and solubility of proteins in solution. This research examines the effect of alpha-, beta-, and gamma-CDs on: (1) stability, (2) encapsulation, and (3) release of insulin from ethylcellulose microcapsules. All CDs improved thermal stability of insulin by lowering the enthalpy of unfolding by 16-52%. alpha- and gamma-CDs also increased the encapsulation efficiency of insulin and improved uniformity of the microcapsule formulations. Two mathematical models were proposed to account for insulin release and consisted of multiple zero order and first order input processes, and a single first order output process. All CDs decreased the initial burst release of insulin by up to 30%. This research demonstrates the potential for CDs to improve stability, uniformity, and encapsulation of proteins in microcapsule formulations.

Comparison of white light and narrow band high definition images in predicting colon polyp histology, using standard colonoscopes without optical magnification

BACKGROUND AND STUDY AIMS

Narrow band imaging (NBI) with optical magnification is useful in predicting colon polyp histology. As magnifying endoscopes are not routinely available, we investigated the use of NBI and high definition white light imaging in determining polyp histology, using images obtained with colonoscopes without optical magnification.

PATIENTS AND METHODS

Images (white light and NBI) of colon polyps less than 10 mm in diameter were collected prospectively from patients undergoing screening colonoscopy and digitally stored. Two endoscopists later reviewed all images and predicted polyp histology as neoplastic or non-neoplastic using a modified Kudo classification. Comparison was made with histopathology.

RESULTS

Separate white light and NBI images of 80 polyps (49 neoplastic, 31 non-neoplastic) from 63 patients were recorded. Mean polyp size was 5.1 +/- 2.1 mm (5.4 +/- 2.2 neoplastic; 4.4 +/- 1.8 non-neoplastic; P = 0.02). In a pooled analysis, NBI correctly predicted neoplastic histology in 93 of 98 images (sensitivity 95 %, positive predictive value [PPV] 94 %) whereas white light did so in 58 of 98 images (sensitivity 59 %, PPV 79 %). NBI correctly predicted non-neoplastic histology in 56 of 62 images (specificity 90 %, negative predictive value [NPV] 92 %) whereas white light did so in 47 of 62 images (specificity 76 %, NPV 54 %).

CONCLUSIONS

NBI without optical magnification was more accurate in predicting colon polyp histology compared with white light imaging. Image quality and confidence in histology were significantly higher in the NBI group. NBI without optical magnification may be useful in predicting colon polyp histology.

The impact of endoscopic ultrasonography with fine needle aspiration (EUS-FNA) on esophageal cancer staging: a survey of thoracic surgeons and gastroenterologists

Accurate staging of esophageal cancer is critical to achieving optimal treatment outcomes. End-oscopic ultrasound with fine needle aspiration (EUS-FNA) has emerged as a valuable tool for locoregional staging. However, it is unclear how different physician specialties perceive the benefit of EUS-FNA for esophageal cancer staging, and thus utilize this modality in clinical practice. A survey regarding utilization of EUS-FNA in esophageal cancer was distributed to 211 thoracic surgeons and 251 EUS-capable gastroenterologists. Seventy-six thoracic surgeons (36%) and 78 gastroenterologists (31%) responded to the survey. Most surgeons (75%) use EUS to stage potentially resectable esophageal cancer 75% of the time. Surgeons using EUS less often are less likely to have access to high-quality EUS services than their peers. Fewer surgeons believe EUS is the most accurate test for T and N-staging (84% and 71%, respectively) as compared with gastroenterologists (97% and 96%, P < 0.01 for both). Most endosonographers (68%) decide whether to dilate a malignant esophageal stricture to complete the staging exam on a case-by-case basis. Surgeons disagree as to whether involvement of celiac lymph nodes should preclude esophagectomy in distal esophageal cancer. While most thoracic surgeons have embraced EUS-FNA as the most accurate locoregional staging modality in esophageal cancer, this attitude is not fully reflected in utilization patterns due to a lack of quality EUS services in some centers. Controversial areas that warrant further study include dilation of malignant strictures to facilitate EUS staging, and the implication of involved celiac lymph nodes on management.

Ornithine transcarbamylase deficiency unmasked because of gastrointestinal bleeding

Ornithine transcarbamylase (OTC) is a mitochondrial-matrix enzyme that catalyzes conversion of ornithine and carbamyl phosphate to citrulline, the second step in the urea cycle. The urea cycle is the most important pathway to detoxification of ammonia in human beings. Ornithine transcarbamylase deficiency (OTCD) is the most common urea cycle disorder, inherited as an X-linked disorder that can cause fatal hyperammonemia in male newborns. Women with OTCD have a variable expression of their disease, the variability being determined by lyonization (random inactivation) of the X chromosome. We report a case of a 28-year-old woman who presented with hyperammonemic encephalopathy that was precipitated by a gastrointestinal bleed unmasking OTCD.

Gallstones, from gallbladder to gut. Management options for diverse complications

Gallstones may be incidental and asymptomatic or painful and accompanied by life-threatening obstruction or infection. A thorough knowledge of potential complications is therefore critical, especially because some asymptomatic stones require prompt treatment. In this article, Drs Agrawal and Jonnalagadda provide valuable instructions for recognizing and treating the various manifestations of gallstone disease.

Lowering dietary saturated fat and total fat reduces the oxidative susceptibility of LDL in healthy men and women

The present study examined the effects of reducing dietary total fat and saturated fat (SFA) on LDL oxidative susceptibility in 27 healthy men and women (age 24-65 y). Each subject consumed each of three diets for 8 wk: an average American diet (AAD, 34% energy from fat, 15% from SFA), a Step-1 diet (29% fat, 9% SFA) and a very low SFA diet (Low-Sat, 25% fat, 6% SFA). In vitro LDL oxidation was assessed by copper-mediated oxidation, as measured by the kinetics of conjugated diene formation and lipid peroxide formation. Compared with the AAD, plasma LDL-cholesterol (LDL-C) and HDL cholesterol levels were 8% lower (P: = 0.16 and P: = 0.11, respectively), in subjects when they consumed the Step-1 diet and 11% (P: < 0.03) and 14% (P: < 0.057) lower, respectively, when they consumed the Low-Sat diet. Conjugated diene production and oxidation rate were 7% (P: < 0. 05) and 9% (P: < 0.05) lower, respectively. The reduction of lipid peroxide formation was 9% (P: < 0.05) in subjects when they consumed the Low-Sat diet vs. the AAD. In addition, lipid peroxide and conjugated diene formation were positively correlated with plasma total and LDL-C and apolipoprotein B (apo B) levels (r = 0.5-0.6, P: < 0.001), suggesting that quantity of LDL is an important determinant of oxidative modification. Furthermore, at the same level of apo B or LDL-C, LDL from subjects when they consumed either Step-1 or Low-Sat diets was less susceptible (P: < 0.05) to oxidation than those when they consumed the AAD, suggesting that qualitative changes also affect LDL oxidative susceptibility. Therefore, the benefits of lowering dietary SFA may extend beyond decreasing LDL-C levels and include favorable qualitative changes in LDL that further decrease risk of coronary heart disease.

Purification and characterization of flavokinase from Neurospora crassa

The ATP-dependent phosphorylation of riboflavin to FMN by flavokinase is the key step in flavin biosynthesis. Flavokinase has been purified from a fungal source for the first time. The enzyme purified from a cell wall lacking mutant of Neurospora crassa, slime, is a monomer of M(r) 35.5 kDa with maximal activity at alkaline pH and high temperature (55 degrees C). The K(m) for both substrates is the lowest reported for flavokinase from any source so far (120 nM for riboflavin and 210 nM for MgATP2-). The enzyme exhibits preference for Mg2+ over Zn2+ as the essential activator and is also significantly activated by several cations. Activation by orthophosphate may be physiologically relevant for the intracellular regulation of flavokinase.

Effects of the National Cholesterol Education Program's Step I and Step II dietary intervention programs on cardiovascular disease risk factors: a meta-analysis

BACKGROUND

Plasma lipid and lipoprotein responses have been variable in dietary intervention studies.

OBJECTIVE

The objective of this study was to evaluate the effects of the National Cholesterol Education Program's Step I and Step II dietary interventions on major cardiovascular disease risk factors using meta-analysis.

DESIGN

MEDLINE was used to select 37 dietary intervention studies in free-living subjects published from 1981 to 1997.

RESULTS

Step I and Step II dietary interventions significantly decreased plasma lipids and lipoproteins. Plasma total cholesterol (TC), LDL cholesterol, triacylglycerol, and TC:HDL cholesterol decreased by 0.63 mmol/L (10%), 0.49 mmol/L (12%), 0.17 mmol/L (8%), and 0.50 (10%), respectively, in Step I intervention studies, and by 0.81 mmol/L (13%), 0.65 mmol/L (16%), 0.19 mmol/L (8%), and 0.34 (7%), respectively, in Step II intervention studies (P < 0.01 for all). HDL cholesterol decreased by 7% (P = 0.05) in response to Step II but not to Step I dietary interventions. Positive correlations between changes in dietary total and saturated fatty acids and changes in TC and LDL and HDL cholesterol were observed (r = 0.59, 0.61, and 0.46, respectively; P < 0.001). Multiple regression analyses showed that for every 1% decrease in energy consumed as dietary saturated fatty acid, TC decreased by 0.056 mmol/L and LDL cholesterol by 0.05 mmol/L. Moreover, for every 1-kg decrease in body weight, triacylglycerol decreased by 0.011 mmol/L and HDL cholesterol increased by 0.011 mmol/L. Exercise resulted in greater decreases in TC, LDL cholesterol, and triacylglycerol and prevented the decrease in HDL cholesterol associated with low-fat diets.

CONCLUSION

Step I and Step II dietary interventions have multiple beneficial effects on important cardiovascular disease risk factors.

Orthophosphate is a non-essential activator of Vigna radiata flavokinase

The ATP-dependent phosphorylation of riboflavin to FMN by flavokinase from Vigna radiata was activated by orthophosphate (Pi) in a concentration dependent manner. Pi affected both the K(m) and Vmax, indicating that it is a non-essential, mixed type activator. The extent of activation by Pi was dependent on the cation (Mg2+ or Zn2+). Activation by other anions could be correlated to similarity to Pi in molecular size and structure. These observations suggest the presence of a binding site(s) for a phosphate-like anion on flavokinase.

Activation of enzymatic catalysis

Modulation of enzyme activity by inhibition and activation plays an important physiological role in regulation of cellular metabolism. Compared to the wealth of information available regarding inhibition of metabolic pathways, little is known about activation. Limited proteolysis of zymogens exemplifies irreversible activation. Reversible activation may involve post-translational modifications or dissociable binding of small molecules. Sometimes, chemical modification may also activate enzymes. The influence of small molecules on the reversible binding and activation of enzymes is summarized.

Combinatorial synthesis and screening of a chemical library of 1,4-dihydropyridine calcium channel blockers

Solid-phase synthesis of a 300-member pharmacophore library of 1,4-dihydropyridines from keto ester, diketone and aldehyde building blocks on a cleavable amine polymeric support is described. Screening and serial deconvolution of the combinatorial library has resulted in identification of known and new potent calcium channel blockers.

Perils of partitioning: A case study of flavins and flavokinase

Partitioning is a common procedure for the separation of two solutes from a solution based on their differential solubility in an immiscible solvent. This has been widely used to quantitate riboflavin, flavin mononucleotide (FMN), and flavin adenine dinucleotide in aqueous samples by extraction with water-saturated benzyl alcohol. Here we report that the partitioning of riboflavin and FMN is affected by the presence of each other in a concentration-dependent manner, thus rendering this procedure unsuitable for quantitation. Direct quantitation of FMN formed in assays for flavokinase from Vigna radiata shows that kinetic analyses using a partition-based assay lead to erroneous conclusions.

Candida albicans osteomyelitis in a liver transplant recipient: a case report and review of the literature

A 51-year-old man developed fever and back pain 2 months after orthotopic liver transplantation for end-stage liver disease secondary to chronic hepatitis C infection. CT scan demonstrated destructive lesions in T12 suggestive of osteomyelitis. Aspiration biopsy of the vertebra revealed granulomatous inflammation and yeast forms; culture yielded Candida albicans. The patient improved with intravenous amphotericin B and 5-fluorocytosine and did not require surgical intervention. Candida osteomyelitis is a rare condition and to our knowledge it has not been reported before in liver transplant recipients. Awareness of this potential complication may shorten the delay in making the definitive diagnosis, which in turn may increase the likelihood of a response without sequela.

Modulation of cholecystokinin activity by albumin

We found that a variety of cholecystokinin (CCK) receptor ligands bind to bovine serum albumin (BSA). This binding was rapid, fully reversible, temperature independent, of low affinity, and specific for BSA; it depended on the concentration of BSA, the chemical structure of the ligand, and the chemical composition of the incubation medium. BSA also decreased the binding of 125I-labeled CCK octapeptide (125I-CCK-8) to CCK receptors on pancreatic acini and membranes but increased the potency with which CCK-8 inhibited binding of 125I-CCK-8. These counterintuitive findings appeared to result from BSA altering the affinities of CCK-8 for different affinity states of the pancreatic CCK receptor. An alternate hypothesis is that BSA increased the efficacy of CCK-8 such that it bound to receptors and also caused biochemical changes in other receptors that reduced their ability to bind 125I-CCK-8. BSA enhanced the ability of CCK-8 to stimulate amylase secretion from pancreatic acini and to cause contraction of dispersed gastric smooth muscle cells. Thus, CCK can bind to BSA, and the BSA-CCK complex has substantially different activities from the free, uncomplexed hormone.

Multiple (alpha-NH-ubiquitin)protein endoproteases in cells

Ubiquitin is encoded as a variable, spacerless repeat of the gene terminating with an additional amino acid or as a gene coding for a single ubiquitin with a carboxyl-terminal extension of 52 to 80 amino acids. We report the identification and partial purification of enzymes that specifically hydrolyze the peptide bond between ubiquitin-ubiquitin conjugate (Ub-Ubase) or ubiquitin fusion proteins (Ub-Xase). The Ub-Ubase was separated from the Ub-Xase by dye-ligand-Sepharose chromatography. The Ub-Xase was purified further by affinity chromatography on ubiquitin-Sepharose. The fidelity of the endoprotease reaction was assessed by measuring the ability of the released ubiquitin to be activated by ubiquitin-activating enzyme (E1) which requires intact ubiquitin and by sequence analysis of the released carboxyl extension protein with 52 amino acids after endoproteolysis of human ubiquitin with 52-amino acid carboxyl extension. The failure of both Ub-Ubase and Ub-Xase to cleave a mutant ubiquitin-Gly-76----Ala-metallothionein showed that the endoproteases distinguish Gly-X from an Ala-X peptide bonds.

Ubiquitin fusion augments the yield of cloned gene products in Escherichia coli

Despite the availability of efficient transcription and translation signals, some heterologous gene products are not adequately expressed when introduced into prokaryotes and eukaryotes. An expression system has been established in Escherichia coli to increase the yield of cloned gene products, where the C terminus of ubiquitin was fused to the N terminus of unstable or poorly expressed proteins. Fusion of ubiquitin to yeast metallothionein or to the alpha subunit of the adenylate cyclase-stimulatory GTP-binding protein increased the yield from undetectable to 20% of the total cellular protein. A ubiquitin-N alpha-protein hydrolase has been partially purified from rabbit reticulocytes; this enzyme faithfully cleaves the junction peptide bound between the C-terminal Gly-76 of ubiquitin and the fusion protein. The increased yield of cloned gene products is very likely due to increased stability and/or more efficient translation of the fusion proteins. Possible mechanisms for the augmentation of ubiquitin fusion-protein expression in prokaryotes and eukaryotes are discussed.

Gene synthesis, expression, and processing of human ubiquitin carboxyl extension proteins

In order to study 1) the mechanisms responsible for generating free ubiquitin monomer and 2) the function of ubiquitin carboxyl extension proteins in eukaryotes, we have developed a system for expression of human ubiquitin carboxyl extension proteins in prokaryotic and eukaryotic hosts. When expressed in Saccharomyces cerevisiae, the intact ubiquitin carboxyl extension proteins were rapidly processed to free ubiquitin monomer and extension protein. Furthermore, expression in this host conferred a slow growth phenotype mediated by the extension protein. Expression in Escherichia coli did not result in processing of the fusion proteins. However, when the expressed fusion proteins were purified from E. coli and incubated with a rabbit reticulocyte extract, the proteins were rapidly processed to free ubiquitin monomer and extension protein. These results show that human ubiquitin carboxyl extension proteins are processed to ubiquitin and extension protein when expressed in eukaryotic but not prokaryotic cells and that pre- and co-translational events are not necessary for their processing. Establishment of this system will allow for large scale purification of these proteins which will aid future studies on the function and structure of ubiquitin carboxyl extension proteins, as well as the mechanisms responsible for their processing.

Ubiquitin carboxyl-terminal peptides. Substrates for ubiquitin activating enzyme

The carboxyl terminus of ubiquitin is activated in the presence of ATP to enter the ubiquitin cycle in cells. Peptides corresponding to the COOH-terminal region of ubiquitin were synthesized to investigate their effects on the ATP/ubiquitin-dependent proteolytic pathway. Their activities in the PPi exchange assay with ubiquitin activating enzyme (E1) were proportional to their length. The hexapeptide Ac-Leu-Arg-Leu-Arg-Gly-Gly reacted with ATP to form an enzyme-adenylate-hexapeptide complex and at high concentrations was 20-25% as active as human ubiquitin in the PPi exchange assay with E1. However, the hexapeptide was not transferred to the sulfhydryl "thiol" site on E1. In addition, the COOH-terminal peptides did not support the degradation of 125I-bovine serum albumin in the reticulocyte lysate system. A nonhomologous peptide of equivalent length was inactive in all assays. Thus, synthetic COOH-terminal peptide(s) of ubiquitin can partially substitute for ubiquitin in its reactions with E1 but do not support subsequent steps of the energy-dependent proteolytic pathway. These results show that it may be possible to design small molecules that either serve as substrates or inhibitors for other specific steps in ubiquitin-dependent pathways.

Expression and accurate processing of yeast penta-ubiquitin in Escherichia coli

An expression vector (pSJyub-5) was constructed which contained five repeats of the "yeast ubiquitin gene" regulated by a heat-inducible lambda PL promoter. The vector, when expressed in Escherichia coli, produced a penta-ubiquitin of approximately 42 kDa. Purified penta-ubiquitin was found to be as active as the human mono-ubiquitin in the in vitro ATP/ubiquitin-dependent proteolytic assay of the reticulocyte lysate, indicating that the expressed gene product was recognized by the enzymes involved in the ATP/ubiquitin-dependent proteolytic pathway. The inability of penta-ubiquitin to act as a substrate in the pyrophosphate exchange reaction with the ubiquitin-activating enzyme E1 suggested that it had a carboxyl-terminal Asn, in agreement with the nucleotide sequence. In E. coli, the expressed penta-ubiquitin was processed correctly to mono-ubiquitin. The fidelity of processing in E. coli was confirmed by the following observations. The amino acid compositions of the processed mono-ubiquitin and human ubiquitin were similar. The 1H NMR spectrum of peaks representing amide hydrogens of the carboxyl-terminal Arg-74, Gly-75, and Gly-76 of the processed mono-ubiquitin was identical with that of human ubiquitin. The immunoreactivity of processed mono-ubiquitin and human ubiquitin against polyclonal antibodies that recognized epitope(s) only on the carboxyl terminus of ubiquitin were similar. The human and processed mono-ubiquitin were equally active in degrading 125I-bovine serum albumin in the ATP/ubiquitin-dependent in vitro proteolytic assay with reticulocyte lysates. In the pyrophosphate exchange assay with isolated ubiquitin activating enzyme E1, they were also equally reactive, confirming that the expressed and processed ubiquitin contained an intact carboxyl-terminal Gly-76. Purified penta-ubiquitin should prove to be a useful substrate for identifying and isolating processing enzyme(s) involved in the ATP/ubiquitin-dependent proteolytic pathway.

Gene synthesis, expression, structures, and functional activities of site-specific mutants of ubiquitin

To study the structure and function of ubiquitin we have chemically synthesized a ubiquitin gene that encodes the amino acid sequence of animal ubiquitin, inserting a series of restriction enzyme sites that divide the gene into eight "mutagenesis modules." A series of site-specific mutations were constructed to selectively perturb various regions of the molecule. The mutant genes were expressed in a large quantity of Escherichia coli, and the modified proteins were purified. To determine the structural effects of the amino acid substitutions, the solution structure of ubiquitin was investigated by two-dimensional NMR and each of the mutant proteins were screened for structural perturbations. With one exception, virtually no changes were seen other than at the point of mutation. Functional studies of the mutant proteins with the ubiquitin-activating enzyme E1 and in the reticulocyte protein degradation assay were used to identify regions of the molecule important to ubiquitin's activity in intracellular proteolysis.