Autoantibodies to αS1-casein are induced by breast-feeding

Structural Analysis of Breast-Milk αS1-Casein: An α-Helical Conformation Is Required for TLR4-Stimulation

Breast-milk αS1-casein is a Toll-like receptor 4 (TLR4) agonist, whereas phosphorylated αS1-casein does not bind TLR4. The objective of this study was to analyse the structural requirements for these effects. In silico analysis of αS1-casein indicated high α-helical content with coiled-coil characteristics. This was confirmed by CD-spectroscopy, showing the α-helical conformation to be stable between pH 2 and 7.4. After in vitro phosphorylation, the α-helical content was significantly reduced, similar to what it was after incubation at 80 °C. This conformation showed no in vitro induction of IL-8 secretion via TLR4. A synthetic peptide corresponding to V77-E92 of αS1-casein induced an IL-8 secretion of 0.95 ng/mL via TLR4. Our results indicate that αS1-casein appears in two distinct conformations, an α-helical TLR4-agonistic and a less α-helical TLR4 non-agonistic conformation induced by phosphorylation. This is to indicate that the immunomodulatory role of αS1-casein, as described before, could be regulated by conformational changes induced by phosphorylation.

Validation of CSN1S1 transcriptional expression, promoter methylation, and prognostic power in breast cancer using independent datasets

Breast cancer ranked second among most frequent cancer in the world playing a significant role in mortality rate. Having prior knowledge on differentially expressed genes in breast cell carcinoma elucidated important indications to understand the molecular mechanism underneath breast carcinogenesis. In this study we have investigated the distinguished CSN1S1 expression in human breast cancer. We have analyzed CSN1S1 mRNA expression between cancer and normal tissues using TCGA datasets. Moreover, analysis including promoter methylation, mutations, prognosis, co-expression, gene ontology, and pathways of CSN1S1 were performed by the TCGA Wanderer, UCSC Xena, cBioPortal, PrognoScan, UALCAN, and Enricher server. We have observed low mRNA expression and high promoter methylation of CSN1S1 in cancer tissues compared to normal tissues. Furthermore, we have also identified low mRNA expression in clinicopathological patients, as well as 9 deleterious mutations with highly co-expressed protein MRC1, and significantly related signaling pathways. We have found a positive correlation between the lower expression of CSN1S1 and patients surviving with breast cancer. Here we have concluded that CSN1S1 acts as a biomarker for the surveillance and prognosis of breast cancer, and also works as a novel therapeutic target at the molecular and pathway levels.

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Low transcriptional expression and low survival rate of CSN1S1 in breast cancer.

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The investigation of clinical profiles and mutational positions of CSN1S1 in breast cancer.

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The investigation of gene ontology and signaling pathway of CSN1S1 and their co-expressed genes.

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We identified CSN1S1 and also their co-expressed proteins are the potential biomarkers in breast cancer.

The Intake of a Cafeteria Diet in Nursing Rats Alters the Breast Milk Concentration of Proteins Important for the Development of Offspring

We aimed to analyse the effects of maternal intake of an unbalanced diet during lactation in the composition and the levels of proteins present in milk. Milk samples from control nursing dams (C-dams) or from nursing dams fed a cafeteria diet during lactation (CAF-dams) were obtained. We conducted a proteomic approach to identify significantly altered proteins in breast milk of C- and CAF-dams, and evaluated the levels of leptin, adiponectin and irisin for their implication in energy homeostasis. One-dimensional SDS-polyacrylamide gel electrophoresis (SDS-PAGE), followed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), revealed that the bands that presented a lower intensity in CAF-dams than control contain some caseins (α-S1-casein, α-S2-casein like B, and β-casein), α-lactalbumin and haptoglobin. Leptin and adiponectin levels were greater in the breast milk of CAF-dams than in controls, while levels of irisin were lower. In summary, the relative concentration of bioactive peptides was influenced by maternal diet consumption during lactation; these changes at early stages of life could influence the phenotypic traits of the offspring.

Human αS1-casein induces IL-8 secretion by binding to the ecto-domain of the TLR4/MD2 receptor complex

BACKGROUND

The milk protein α_S1-casein was recently reported to induce secretion of proinflammatory cytokines via Toll-like receptor 4 (TLR4). In this study, α_S1-casein was identified as binder of theTLR4 ecto domain.

METHODS

IL-8 secretion after stimulation of TLR4/MD2 (myeloid differentiation factor 2)/CD14 (cluster of differentiation 14)-transfected HEK293 cells (TLR4⁺) and Mono Mac 6 cells (MM6) with recombinant α_S1-casein, or LPS as control was monitored. Binding of α_S1-casein to TLR4 was quantified by microscale thermophoresis (MST).

RESULTS

α_S1-casein induced secretion of IL-8 in TLR4⁺ cells and in MM6 cells with a six-times higher final IL-8 concentration in supernatants. IL-8 secretion was inhibited by intracellular TLR4-domain antagonist TAK-242 with an IC₅₀-value of 259.6 nM, by ecto-domain TLR4 antagonistic mianserin with 10-51 μM and by anti-CD14-IgA. The binding constants (K_D) of α_S1-casein to the TLR4, MD2, and CD14 were 2.8 μM, 0.3 μM and 2.7 μM, respectively. Finally, α_S1-casein showed a higher affinity to TLR4/MD2 (K_D: 2.2 μM) compared to LPS (K_D: 8.2 μM).

CONCLUSION

Human α_S1-casein induced proinflammatory effects are dependent upon binding to the TLR4 ectodomain and the presence of CD14. α_S1-casein displayed stronger TLR4 agonistic activity than LPS via a different mode of action.

GENERAL SIGNIFICANCE

Breast milk protein α_S1-casein is a proinflammatory cytokine.

Ser71 of αS1-Casein is Phosphorylated in Breast Milk-Evidence from Targeted Mass Analysis

SCOPE

The casein phosphoproteins in mother's milk supply calcium and phosphate ions and make them biologically available to the newborn. Human αS1-casein is of particular interest being also an autoantigen and proinflammatory cytokine. Phosphorylation of αS1-casein by casein kinase 2 completely abolishes binding to toll-like receptor 4 and proinflammatory effects. It is, however, not known, which amino acids are affected. Therefore, breast milk samples were analyzed in an effort to detect the phosphorylation sites of αS1-casein.

METHODS AND RESULTS

Breast milk samples were tryptically digested. Target tandem MS analysis confirmed the known phosphorylation sites S33 and S41; evidence for pS89 was found in some samples. Experimental support for the presence of pS31 and pS34 was weak. Phosphorylation of a new site in αS1-casein, S71, was reproducibly measured in all samples, albeit at much lower intensity than pS33 and pS41.

CONCLUSION

Phospho-occupancy rates varied greatly and could not be confidently correlated to other parameters within the cohort of 20 donors. The new phosphosite S71 is located in the neighborhood of the serine-rich region and may contribute to the cluster of high charge density at normal milk pH, likely exerting an influence on protein tertiary structure and thus function.

Identification of a Potent Allosteric Inhibitor of Human Protein Kinase CK2 by Bacterial Surface Display Library Screening

Human protein kinase CK2 has emerged as promising target for the treatment of neoplastic diseases. The vast majority of kinase inhibitors known today target the ATP binding site, which is highly conserved among kinases and hence leads to limited selectivity. In order to identify non-ATP competitive inhibitors, a 12-mer peptide library of 6 × 10⁵ variants was displayed on the surface of E. coli by autodisplay. Screening of this peptide library on variants with affinity to CK2 was performed by fluorophore-conjugated CK2 and subsequent flow cytometry. Single cell sorting of CK2-bound E. coli yielded new peptide variants, which were tested on inhibition of CK2 by a CE-based assay. Peptide B2 (DCRGLIVMIKLH) was the most potent inhibitor of both, CK2 holoenzyme and the catalytic CK2α subunit (IC₅₀ = 0.8 µM). Using different ATP concentrations and different substrate concentrations for IC₅₀ determination, B2 was shown to be neither ATP- nor substrate competitive. By microscale thermophoresis (MST) the K_D value of B2 with CK2α was determined to be 2.16 µM, whereas no binding of B2 to CK2β-subunit was detectable. To our surprise, besides inhibition of enzymatic activity, B2 also disturbed the interaction of CK2α with CK2β at higher concentrations (≥25 µM).

Naphthol AS-E Phosphate Inhibits the Activity of the Transcription Factor Myb by Blocking the Interaction with the KIX Domain of the Coactivator p300

The transcription factor c-Myb is highly expressed in hematopoietic progenitor cells and controls the transcription of genes important for lineage determination, cell proliferation, and differentiation. Deregulation of c-Myb has been implicated in the development of leukemia and certain other types of human cancer. c-Myb activity is highly dependent on the interaction of the c-Myb with the KIX domain of the coactivator p300, making the disruption of this interaction a reasonable strategy for the development of Myb inhibitors. Here, we have used bacterial Autodisplay to develop an in vitro binding assay that mimics the interaction of Myb and the KIX domain of p300. We have used this binding assay to investigate the potential of Naphthol AS-E phosphate, a compound known to bind to the KIX domain, to disrupt the interaction between Myb and p300. Our data show that Naphthol AS-E phosphate interferes with the Myb-KIX interaction in vitro and inhibits Myb activity in vivo. By using several human leukemia cell lines, we demonstrate that Naphthol AS-E phosphate suppresses the expression of Myb target genes and induces myeloid differentiation and apoptosis. Our work identifies Naphthol AS-E phosphate as the first low molecular weight compound that inhibits Myb activity by disrupting its interaction with p300, and suggests that inhibition of the Myb-KIX interaction might be a useful strategy for the treatment of leukemia and other tumors caused by deregulated c-Myb.

Development of a surface display ELISA to detect anti-IgG antibodies against bovine αS1-casein in human sera

The aim of the present study was to develop a surface display ELISA (SD-ELISA) for IgG-serum reaction against bovine casein αS1 (CSN1S1). In a SD-ELISA, the antigen is displayed on the surface of Escherichia coli using the autodisplay technology and whole cells of E. coli are used to coat the microplates for serum testing. After establishing the setup of the SD-ELISA with polyclonal rabbit antiserum against bovine CSN1S1, the SD-ELISA was validated with 20 human sera, of which 10 sera were proven to have an IgG-mediated reaction against bovine CSN1S1 and 10 sera were shown to be negative for this reaction. Receiver operating characteristics (ROC) analysis revealed sensitivity of 100% and a specificity of 100% at a cut-off value of 0.133. Furthermore, human serum of 48 patients with known reactivity against human CSN1S1 (31 positive and 17 negative) was examined by the newly developed SD-ELISA to exclude cross-reactivity. Twenty human sera showed an IgG-mediated reaction against bovine CSN1S1. Eleven of these sera were positive for the reactivity against human CSN1S1, and nine were negative. In conclusion it was demonstrated that the performance of SD-ELISA is comparable to established ELISA without loss in sensitivity or specificity. Based on the advantages of this method - in particular no need for time-consuming and expensive antigen production and purification - the SD-ELISA is a potent alternative to convenient methods for identification and especially high-throughput screening of new antigens in the field of food allergies.

Human casein alpha s1 (CSN1S1) skews in vitro differentiation of monocytes towards macrophages

Background

The milk-derived protein human Casein alpha s1 (CSN1S1) has recently been detected in blood cells and was shown to possess proinflammatory properties. In the present study, we investigated the effect of CSN1S1 on the differentiation of monocytes.

Methods

Primary human monocytes were stimulated with recombinant CSN1S1 and compared to cells stimulated with GM-CSF/IL-4 or M-CSF/IFNγ. Morphological changes were assessed by microscopy and quantification of surface markers of differentiation by FACS analysis. Phagocytic activity of CSN1S1 stimulated cells was measured by quantification of zymosan labeled particle uptake. The role of mitogen activated protein kinases for CSN1S1-induced differentiation of monocytes and proinflammatory cytokine expression was assessed by supplementation of specific inhibitors.

Results

CSN1S1 at a concentration of 10 μg/ml resulted in morphological changes (irregular shape, pseudopodia) and aggregation of cells, comparable to changes observed in M-CSF/IFNγ differentiated macrophages. Surface marker expression was altered after 24 h with an upregulation of CD14 (mean 2.5 fold) and CD64 (1.9 fold) in CSN1S1 stimulated cells. CSN1S1 treated cells showed a characteristic surface marker pattern for macrophages after 120 h of incubation (CD14^high, CD64^high, CD83^low, CD1a^low) comparable to changes observed in M-CSF/IFNγ treated monocytes. Furthermore, phagocytic activity was increased 1.4 and 1.9 fold following stimulation with 10 μg/ml CSN1S1 after 24 and 48 h, respectively. Early GM-CSF, but not GM-CSF/IL-4 induced differentiation of monocytes towards dendritic cells (DC) was inhibited by addition of CSN1S1. Finally, CSN1S1 induced upregulation of CD14 was impeded by inhibition of ERK1/2, while inhibition of the mitogen activated protein kinases JNK and p38 did not influence cellular differentiation. However, JNK and p38 inhibitors impeded CSN1S1 induced secretion of the proinflammatory cytokines IL-1b or IL-6.

Conclusions

CSN1S1 skews in vitro differentiation of monocytes towards a macrophage-like phenotype. Data is accumulating that functions of CSN1S1 are beyond nutritional properties and include immunomodulatory effects.