Demonstration that a human 26S proteolytic complex consists of a proteasome and multiple associated protein components and hydrolyzes ATP and ubiquitin-ligated proteins by closely linked mechanisms

It is known that two types of high-molecular-mass protease complexes are present in the cytosol of mammalian cells; a 20S latent multicatalytic proteinase named the proteasome, and a large proteolytic complex with an apparent sedimentation coefficient of 26S that catalyzes ATP-dependent breakdown of proteins conjugated with ubiquitin. In this work, we first demonstrated that a low concentration of SDS was required for activation of the latent proteasome, whereas the 26S complex degraded substrates for proteasomes in the absence of SDS. Moreover, the 26S complex was greatly stabilized in the presence of 2 mM ATP and 20% glycerol. Based on these characteristics, we next devised a novel procedure for purification of the 26S proteolytic complexes from human kidney. In this procedure, the proteolytic complexes were precipitated from cytoplasmic extracts by ultracentrifugation for 5 h at 105000 x g, and the large 26S complexes were clearly separated from the 20S proteasomes by molecular-sieve chromatography on a Biogel A-1.5 m column. The 26S enzyme was then purified to apparent homogeneity by successive chromatographies on hydroxyapatite and Q Sepharose, then by glycerol density-gradient centrifugation. Electrophoretic and immunochemical analyses showed that the purified human 26S complex consisted of multiple subunits of proteasomes with molecular masses of 21-31 kDa and 13-15 protein components ranging in molecular mass over 35-110 kDa, which were directly associated with the proteasome. The purified 26S proteolytic complex degraded 125I-labeled lysozyme-ubiquitin conjugates in an ATP-dependent manner. The 26S enzyme also showed high ATPase activity, which was copurified with the complex. Vanadate and hemin strongly inhibited not only ATP cleavage, but also ATP-dependent breakdown of ubiquitinligated proteins, suggesting that the 26S complex hydrolyzes ATP and ubiquitinated proteins by closely linked mechanisms. These findings indicate that the 26S complex consists of a proteasome with proteolytic function and multiple other components including an ATPase that regulates energy-dependent, ubiquitin-mediated protein degradation.

Purification and characterization of the 26S proteasome complex catalyzing ATP-dependent breakdown of ubiquitin-ligated proteins from rat liver

An ATP/ubiquitin-dependent proteasome complex with an apparent sedimentation coefficient of 26S was purified from rat liver to near homogeneity by an improved method based on procedures reported previously. Two electrophoretically distinct forms of the 26S complex, named 26S alpha and 26S beta, with very similar subunit compositions were found not only in purified preparations but also in crude extracts, indicating that the 26S proteasome is present as two isoforms. The 26S proteasome was shown to degrade multi-ubiquitinated, but not unmodified, lysozymes in an ATP-dependent fashion, to have ATPase activity supplying energy for proteolysis, and to contain isopeptidase activity to generate free ubiquitin Mg2+/ATP-dependently. The 26S proteasome also catalyzed the ATP-independent hydrolyses of three types of fluorogenic peptides with basic, neutral, and acidic amino acids at their cleavage sites, respectively. These peptides are also good substrates for the 20S proteasome, but their degradation by the free 20S proteasome and by its assembled form in the 26S complex differ markedly, suggesting a functional difference between the two forms of proteasomes. Electrophoretic and immunochemical analyses showed that the large 26S complex was composed grossly of two different structures: a core 20S proteasome with multicatalytic proteinase functions and an associated part possibly with a regulatory role. These two structures both consisted of multiple polypeptides with molecular masses of 21-31 and 35-110 kDa, respectively. The subunit multiplicity of the rat 26S proteasome closely resembled that of the human counterpart, showing only minor species-specific differences in certain components. The assembly of this multi-component complex was found not to involve a sulfhydryl bond. Electrophoretic peptide mapping with lysyl-endopeptidase indicated the non-identity of the multiple subunits of the 26S proteasome. From these structural and functional characteristics, the 26S proteasome, which is widely distributed in mammals, is suggested to be a new type of multi-molecular complex catalyzing the soluble energy- and ubiquitin-dependent proteolytic pathway.

Parvovirus B19: A Cause of Sepsislike Syndrome in an Infant

Parvovirus B19 (PB19) is an important human pathogen that results in a wide spectrum of clinical outcomes, from mild, self-limiting erythema infectiosum in immunocompetent children and arthralgia in adults to lethal cytopenia in immunocompromised patients and intrauterine fetal death. However, there have been few reports of PB19 infection in neonates or young infants (aged 28-90 days), and no previous reports contained descriptions of PB19 infection as a cause of sepsislike syndrome in this age group. We report a case of sepsislike syndrome caused by PB19 infection in a 56-day-old infant whose mother had polyarthralgia at the time of his admission. PB19 infection was diagnosed on the basis of positive polymerase chain reaction results for PB19 DNA in the serum and cerebrospinal fluid. Positive immunoglobulin M and negative immunoglobulin G for PB19 suggested acute infection. He was admitted to the ICU because of poor peripheral circulation, but fully recovered without antibiotic administration. After excluding other possible pathogens, PB19 should be suspected as a cause of sepsislike syndrome in young infants, especially those who have close contact with PB19-infected individuals.

Inverse relationship between Fusobacterium nucleatum amount and tumor CD274 (PD-L1) expression in colorectal carcinoma

Objectives

The CD274 (programmed cell death 1 ligand 1, PD-L1)/PDCD1 (programmed cell death 1, PD-1) immune checkpoint axis is known to regulate the antitumor immune response. Evidence also supports an immunosuppressive effect of Fusobacterium nucleatum. We hypothesised that tumor CD274 overexpression might be inversely associated with abundance of F. nucleatum in colorectal carcinoma.

Methods

We assessed tumor CD274 expression by immunohistochemistry and F. nucleatum DNA within tumor tissue by quantitative PCR in 812 cases among 4465 incident rectal and colon cancer cases that had occurred in two prospective cohort studies. Multivariable logistic regression analyses with inverse probability weighting were used to adjust for selection bias because of tissue data availability and potential confounders including microsatellite instability status, CpG island methylator phenotype, LINE-1 methylation level and KRAS, BRAF and PIK3CA mutations.

Results

Fusobacterium nucleatum DNA was detected in tumor tissue in 109 (13%) cases. Tumor CD274 expression level was inversely associated with the amount of F. nucleatum in colorectal cancer tissue (P = 0.0077). For one category-unit increase in three ordinal F. nucleatum categories (negative vs. low vs. high), multivariable-adjusted odds ratios (with 95% confidence interval) of the low, intermediate and high CD274 categories (vs. negative) were 0.78 (0.41-1.51), 0.64 (0.32-1.28) and 0.50 (0.25-0.99), respectively (P trend = 0.032).

Conclusions

Tumor CD274 expression level was inversely associated with the amount of F. nucleatum in colorectal cancer tissue, suggesting that different immunosuppressive mechanisms (i.e. PDCD1 immune checkpoint activation and tumor F. nucleatum enrichment) tend to be used by different tumor subgroups.

Mumps vaccine hesitancy: Current evidence and an evidence-based campaign in Japan

BACKGROUND

Mumps is still endemic in Japan because mumps vaccination is voluntary. In this study, we investigated associations of parental socioeconomic status, family structure, and knowledge/belief about mumps and mumps vaccine with parental decision to vaccinate their children. We also evaluated effectiveness of a campaign based on survey results.

METHODS

We conducted a cross-sectional survey of parents with children aged 1-6 years attending preschools or kindergartens in Tokamachi City, Japan. We assessed the association of parental factors with their decision to vaccinate their children using multivariable logistic regression analyses. We designed a campaign based on the survey results, and compared the number of annual vaccinations at Tokamachi Hospital per the child population aged 1-6 years in Tokamachi City before and after the campaign using a trend test.

RESULTS

In total, 1391 of 1617 (86%) eligible parents completed the survey. Among these parents, 229 (16%) vaccinated their children. In multivariable analyses, higher parental education [odds ratio (OR) = 2.21; 95% CI, 1.59-3.08; P < 0.001], greater knowledge about mumps and the mumps vaccine (OR = 1.88; 95% CI, 1.60-2.21; P < 0.001), and living without grandparents (OR = 1.44; 95% CI, 1.05-1.99; P = 0.024) were significantly associated with parental decision to vaccinate their children. The number of annual vaccinations per the child population significantly increased following the campaign (P < 0.001).

CONCLUSION

Our study showed several sociodemographic factors significantly associated with mumps vaccination. Further research is needed to examine the relevance of our findings to the uptake of other voluntary vaccines among children.

An Empirical Dietary Pattern Associated With the Gut Microbial Features in Relation to Colorectal Cancer Risk

BACKGROUND & AIMS

Epidemiologic evidence for dietary influence on colorectal cancer (CRC) risk through the gut microbiome remains limited.

METHODS

Leveraging 307 men and 212 women with stool metagenomes and dietary data, we characterized and validated a sex-specific dietary pattern associated with the CRC-related gut microbial signature (CRC Microbial Dietary Score [CMDS]). We evaluated the associations of CMDS with CRC risk according to Fusobacterium nucleatum, pks+Escherichia coli, and enterotoxigenic Bacteroides fragilis status in tumor tissue using Cox proportional hazards regression in the Health Professionals Follow-Up Study (1986-2018), Nurses' Health Study (1984-2020), and Nurses' Health Study II (1991-2019).

RESULTS

The CMDS was characterized by high industrially processed food and low unprocessed fiber-rich food intakes. In 259,200 participants, we documented 3854 incident CRC cases over 6,467,378 person-years of follow-up. CMDS was associated with a higher risk of CRC (Ptrend < .001), with a multivariable hazard ratio (HRQ5 vs Q1) of 1.25 (95% CI, 1.13-1.39). The association remained after adjusting for previously established dietary patterns, for example, the Western and prudent diets. Notably, the association was stronger for tumoral F nucleatum-positive (HRQ5 vs Q1, 2.51; 95% CI, 1.68-3.75; Ptrend < .001; Pheterogeneity = .03, positivity vs negativity), pks+E coli-positive (HRQ5 vs Q1, 1.68; 95% CI, 0.84-3.38; Ptrend = .005; Pheterogeneity = .01, positivity vs negativity), and enterotoxigenic Bacteroides fragilis-positive CRC (HRQ5 vs Q1, 2.06; 95% CI, 1.10-3.88; Ptrend = .016; Pheterogeneity = .06, positivity vs negativity), compared with their negative counterparts.

CONCLUSIONS

CMDS was associated with increased CRC risk, especially for tumors with detectable F nucleatum, pks+E coli, and enterotoxigenic Bacteroides fragilis in tissue. Our findings support a potential role of the gut microbiome underlying the dietary effects on CRC.

Enrichment of Bacteroides fragilis and enterotoxigenic Bacteroides fragilis in CpG island methylator phenotype-high colorectal carcinoma

OBJECTIVES

Data support that enterotoxigenic Bacteroides fragilis (ETBF) harbouring the Bacteroides fragilis toxin (bft) gene may promote colorectal tumourigenesis through the serrated neoplasia pathway. We hypothesized that ETBF may be enriched in colorectal carcinoma subtypes with high-level CpG island methylator phenotype (CIMP-high), BRAF mutation, and high-level microsatellite instability (MSI-high).

METHODS

Quantitative PCR assays were designed to quantify DNA amounts of Bacteroides fragilis, ETBF, and each bft gene isotype (bft-1, bft-2, or bft-3) in colorectal carcinomas in the Health Professionals Follow-up Study and Nurses' Health Study. We used multivariable-adjusted logistic regression models with the inverse probability weighting method.

RESULTS

We documented 4476 colorectal cancer cases, including 1232 cases with available bacterial data. High DNA amounts of Bacteroides fragilis and ETBF were positively associated with BRAF mutation (p ≤ 0.0003), CIMP-high (p ≤ 0.0002), and MSI-high (p < 0.0001 and p = 0.01, respectively). Multivariable-adjusted odds ratios (with 95% confidence interval) for high Bacteroides fragilis were 1.40 (1.06-1.85) for CIMP-high and 2.14 (1.65-2.77) for MSI-high, but 1.02 (0.78-1.35) for BRAF mutation. Multivariable-adjusted odds ratios for high ETBF were 2.00 (1.16-3.45) for CIMP-high and 2.86 (1.64-5.00) for BRAF mutation, but 1.09 (0.67-1.76) for MSI-high. Neither Bacteroides fragilis nor ETBF was associated with colorectal cancer-specific or overall survival.

DISCUSSION

The tissue abundance of Bacteroides fragilis is associated with CIMP-high and MSI-high, whereas ETBF abundance is associated with CIMP-high and BRAF mutation in colorectal carcinoma. Our findings support the aetiological relevance of Bacteroides fragilis and ETBF in the serrated neoplasia pathway.

Clinicopathological, molecular, and prognostic features of colorectal carcinomas with KRAS c.34G>T (p.G12C) mutation

Evidence indicates that combinations of anti-EGFR antibodies and KRAS p.G12C (c.34G>T) inhibitors can be an effective treatment strategy for advanced colorectal cancer. We hypothesized that KRAS c.34G>T (p.G12C)-mutated colorectal carcinoma might be a distinct tumor subtype. We utilized a prospective cohort incident tumor biobank (including 1347 colorectal carcinomas) and detected KRAS c.34G>T (p.G12C) mutation in 43 cases (3.2%) and other KRAS mutations (in codon 12, 13, 61, or 146) in 467 cases (35%). The CpG island methylator phenotype (CIMP)-low prevalence was similarly higher in KRAS c.34G>T mutants (52%) and other KRAS mutants (49%) than in KRAS-wild-type tumors (31%). KRAS c.34G>T mutants showed higher CIMP-high prevalence (14%) and lower CIMP-negative prevalence (33%) compared with other KRAS mutants (6% and 45%, respectively; p = 0.0036). Similar to other KRAS mutants, KRAS c.34G>T-mutated tumors were associated with cecal location, non-microsatellite instability (MSI)-high status, BRAF wild type, and PIK3CA mutation when compared with KRAS-wild-type tumors. Compared with BRAF-mutated tumors, KRAS c.34G>T mutants showed more frequent LINE-1 hypomethylation, a biomarker for early-onset colorectal carcinoma. KRAS c.34G>T mutants were not associated with other features, including the tumor tissue abundance of Fusobacterium nucleatum (F. animalis), pks+ Escherichia coli, Bifidobacterium, or (enterotoxigenic) Bacteroides fragilis. Among 1122 BRAF-wild-type colorectal carcinomas, compared with KRAS-wild-type tumors, multivariable-adjusted colorectal cancer-specific mortality hazard ratios (95% confidence interval) were 1.82 (1.05-3.17) in KRAS c.34G>T (p.G12C)-mutated tumors (p = 0.035) and 1.57 (1.22-2.02) in other KRAS-mutated tumors (p = 0.0004). Our study provides novel evidence for clinical and tumor characteristics of KRAS c.34G>T (p.G12C)-mutated colorectal carcinoma.

Long-term yogurt intake and colorectal cancer incidence subclassified by Bifidobacterium abundance in tumor

Evidence suggests a tumor-suppressive effect of the intake of yogurt, which typically contains Bifidobacterium. We hypothesized that long-term yogurt intake might be associated with colorectal cancer incidence differentially by tumor subgroups according to the amount of tissue Bifidobacterium. We utilized the prospective cohort incident-tumor biobank method and resources of two prospective cohort studies. Inverse probability weighted multivariable Cox proportional hazards regression was used to assess differential associations of yogurt intake with the incidence of colorectal carcinomas subclassified by the abundance of tumor tissue Bifidobacterium. During follow-up of 132,056 individuals, we documented 3,079 incident colorectal cancer cases, including 1,121 with available tissue Bifidobacterium data. The association between long-term yogurt intake and colorectal cancer incidence differed by Bifidobacterium abundance (P heterogeneity = 0.0002). Multivariable-adjusted hazard ratios (HRs) (with 95% confidence intervals) in individuals who consumed ≥2 servings/week (vs. <1 serving/month) of yogurt were 0.80 (0.50-1.28) for Bifidobacterium-positive tumor and 1.09 (0.81-1.46) for Bifidobacterium-negative tumor. This differential association was also observed in a subgroup analysis of proximal colon cancer (P heterogeneity = 0.018). Long-term yogurt intake may be differentially associated with the incidence of proximal colon cancer according to Bifidobacterium abundance, suggesting the antitumor effect of yogurt intake on the specific tumor subgroup.