Primary glioblastoma cells for precision medicine: a quantitative portrait of genomic (in)stability during the first 30 passages.

Background: Primary glioblastoma cell (GC) cultures have emerged as a key model in brain tumor research, with the potential to uncover patient-specific differences in therapy response. However, there is limited quantitative information about the stability of such cells during the initial 20-30 passages of culture. Methods: We interrogated 3 patient-derived GC cultures at dense time intervals during the first 30 passages of culture. Combining state-of-the-art signal processing methods with a mathematical model of growth, we estimated clonal composition, rates of change, affected pathways, and correlations between altered gene dosage and transcription. Results: We demonstrate that GC cultures undergo sequential clonal takeovers, observed through variable proportions of specific subchromosomal lesions, variations in aneuploid cell content, and variations in subpopulation cell cycling times. The GC cultures also show significant transcriptional drift in several metabolic and signaling pathways, including ribosomal synthesis, telomere packaging and signaling via the mammalian target of rapamycin, Wnt, and interferon pathways, to a high degree explained by changes in gene dosage. In addition to these adaptations, the cultured GCs showed signs of shifting transcriptional subtype. Compared with chromosomal aberrations and gene expression, DNA methylations remained comparatively stable during passaging, and may be favorable as a biomarker. Conclusion: Taken together, GC cultures undergo significant genomic and transcriptional changes that need to be considered in functional experiments and biomarker studies that involve primary glioblastoma cells.

The Human Glioblastoma Cell Culture Resource: Validated Cell Models Representing All Molecular Subtypes.

Glioblastoma (GBM) is the most frequent and malignant form of primary brain tumor. GBM is essentially incurable and its resistance to therapy is attributed to a subpopulation of cells called glioma stem cells (GSCs). To meet the present shortage of relevant GBM cell (GC) lines we developed a library of annotated and validated cell lines derived from surgical samples of GBM patients, maintained under conditions to preserve GSC characteristics. This collection, which we call the Human Glioblastoma Cell Culture (HGCC) resource, consists of a biobank of 48 GC lines and an associated database containing high-resolution molecular data. We demonstrate that the HGCC lines are tumorigenic, harbor genomic lesions characteristic of GBMs, and represent all four transcriptional subtypes. The HGCC panel provides an open resource for in vitro and in vivo modeling of a large part of GBM diversity useful to both basic and translational GBM research.

Tyrosine phosphorylation profiling via in situ proximity ligation assay.

BACKGROUND: Tyrosine phosphorylation (pTyr) is an important cancer relevant posttranslational modification since it regulates protein activity and cellular localization. By controlling cell growth and differentiation it plays an important role in tumor development. This paper describes a novel approach for detection and visualization of a panel of pTyr proteins in tumors using in situ proximity ligation assay. METHODS: K562 leukemia cells were treated with tyrosine kinase and/or phosphatase inhibitors to induce differences in pTyr levels and mimic cells with different malignant properties. Cells were then probed with one antibody against the pTyr modification and another probe against the detected protein, resulting in a detectable fluorescent signal once the probes were in proximity. RESULTS: Total and protein specific pTyr levels on ABL, SHC, ERK2 and PI3K proteins were detected and samples of control and treated cells were distinguished at the pTyr level using this novel approach. Promising results were also detected for formalin fixed and paraffin embedded cells in the micro array format. CONCLUSIONS: This application of in situ proximity ligation assay is valuable in order to study the pTyr modification of a panel of proteins in large data sets to validate mass spectrometric data and to be combined with tissue microarrays. The approach offers new opportunities to reveal the pTyr signatures in cells of different malignant properties that can be used as biomarker of disease in the future.

Post translational modifications in adenovirus type 2.

We have combined 2-D SDS-PAGE with liquid chromatography-high resolving mass spectrometry (LC-MS) to explore the proteome of the adenovirus type 2 (Ad2) at the level of post translational modifications (PTMs). The experimental design included in-solution digestion, followed by titanium dioxide enrichment, as well as in-gel digestion of polypeptides after separation of Ad2 capsid proteins by 1-D and 2-D SDS-PAGE. All samples were analyzed using LC-MS with subsequent manual verification of PTM positions. The results revealed new phosphorylation sites that can explain the observed trains of protein spots observed for the pIII, pIIIa and pIV proteins. The pIIIa protein was found to be the most highly modified protein with now 18 verified sites of phosphorylation, three sites of nitrated tyrosine and one sulfated tyrosine. Nitrated tyrosines were also identified in pII. Lysine acetylations were detected in pII and pVI. The findings make the Ad2 virion much more complex than hitherto believed.

The phosphoproteome of the adenovirus type 2 virion.

We have used a proteomics approach to identify sites of phosphorylation in the structural proteins of the Adenovirus type 2 particle. This protein modification might play an important role during infection. Peptides from highly purified virus were enriched for phosphorylations and analyzed by liquid chromatography-high-resolving mass spectrometry. Phosphorylations were identified in 11 structural peptides and 29 non-redundant phosphorylation sites were unambiguously assigned to specific amino acid. An unexpected result was the finding of phosphotyrosine in two of the viral polypeptides. The most highly phosphorylated protein was pIIIa with 12 identified phosphorylation sites. An identified preference for proline or leucine residue flanking the phosphorylation sites downstream suggests that cellular kinases are involved in many of the phosphorylations. Structural modeling showed that one site in the hexon is located on the outer side of the virus and could be of importance for the virus when attaching and entering cells.

Optimization of immunoaffinity enrichment and detection: toward a comprehensive characterization of the phosphotyrosine proteome of K562 cells by liquid chromatography-mass spectrometry.

Phosphorylation of protein tyrosine residues regulates many cell functions and has also been proved to be involved in oncogenesis. Thus, the identification of the phosphotyrosine (pTyr) proteome of cells is a very important task. Since tyrosine phosphorylation represents only around 1% of the total human phosphoproteome, the study of pTyr proteins is rather challenging. Here we report the optimization study of the phosphotyrosine proteome using K562 cells as a model system. A substantial segment of the phosphotyrosine proteome of K562 cells was characterized by immunoaffinity enrichment with 4G10 and PYKD1 antibodies followed by LC-MS/MS analysis. 480 non-redundant pTyr peptides corresponding to 342 pTyr proteins were found. 141 pTyr peptides were not described elsewhere. The mass spectrometry approach involving high-resolving FTMS analysis of precursor ions and subsequent detection of CID fragments in a linear ion trap was considered as optimal. For detection of low abundant pTyr peptides pooling of individual immunoaffinity enrichments for one LC-MS/MS analysis was crucial. The enrichment properties of the monoclonal PYKD1 antibody were presented for the first time, also in comparison to the 4G10 antibody. PYKD1 was found to be more effective for protein enrichment (1.2 and 5% efficiency at peptide and protein level correspondingly), while 4G10 showed better results when peptide enrichment was performed (15% efficiency versus 3.6% at protein level). Substantially different subsets of the phosphoproteome were enriched by these antibodies. This finding together with previous studies demonstrates that comprehensive pTyr proteome characterization by immunoprecipitation requires multiple antibodies to be used for the affinity enrichment.

Toward a comprehensive characterization of the phosphotyrosine proteome.

Tyrosine phosphorylation (pTyr) regulates important cell functions and plays a key role in carcinogenesis. The purpose of this study was to perform a comprehensive study of the phosphotyrosine proteome. Immunoaffinity enriched pTyr proteins and peptides from K562 leukemia cells were analyzed with high-resolving liquid chromatography mass spectrometry. Two different antibodies selective for the pTyr modification were used in repeated enrichments to identify as many pTyr peptides as possible. Stringent verification of putative pTyr sites was performed to assure high reliability in the subsequent biological interpretation of the data. Identified pTyr proteins were subjected to pathway analysis by using different analytical tools. In total, 294 pTyr peptides belonging to 217 pTyr proteins were identified, 15 of which had not previously been reported to be modified by pTyr. The pTyr proteins were clustered in six major groups based on the biological functions "cellular signaling", "cell motility and shape", "cell cycle process", "transport", "RNA processing" and "protein processing". The pTyr proteins were mainly positioned in the following cellular compartments: cytoplasm, cytoskeleton, nucleus and ribonucleoprotein complexes. An interesting finding was that many proteins were related to RNA processing and were found to be heterogeneous nuclear ribonucleoproteins. Also, more than half of the novel pTyr proteins were localized to the nucleus, of which three (PBX2, TEAD1 and DIDO1) were classified as transcription factors and two (CENPC1 and MAD2L1) are associated with cell division control.

Detection of tyrosine phosphorylated proteins by combination of immunoaffinity enrichment, two-dimensional difference gel electrophoresis and fluorescent Western blotting.

We describe fluorescence-based 2-D gel electrophoresis methods for visualization of low abundant, cancer relevant tyrosine phosphorylated (pTyr) proteins. The methods investigated were fluorescent Western blotting and two-dimensional difference gel electrophoresis (2-D DIGE) for detection of non-enriched and immunoaffinity enriched pTyr protein patterns. The same anti-phosphotyrosine specific antibody, 4G10, was used for both approaches. The results from fluorescent Western blotting of total proteins and from enriched CyDye DIGE pre-labeled pTyr proteins showed similar down regulation of phosphorylation upon treating of cells from a cancer model system (K562 chronic myeloid leukemia cells) with imatinib. This treatment introduced a known perturbation of phosphorylation that enabled testing of these new approaches to analyze variations in tyrosine phosphorylation levels. Enrichment of pTyr proteins was found highly advantageous for the outcome. Out of a simplified 2-D DIGE experiment of immunoaffinity enriched control and treated pTyr proteins, differential analysis as well as protein identification by mass spectrometry (MS) was possible.

Immunoaffinity enrichments followed by mass spectrometric detection for studying global protein tyrosine phosphorylation.

Phosphorylation of protein tyrosine residues regulates important cell functions and is, when dysregulated, often crucially involved in oncogenesis. It is therefore important to develop and evaluate methods for identifying and studying tyrosine phosphorylated (P-Tyr) proteins. P-Tyr proteins are present at very low concentrations within cells, requiring highly selective enrichment methods to be detected. In this study, we applied immunoaffinity as enrichment step for P-Tyr proteins. Five selected anti-phosphotyrosine antibodies (monoclonal antibodies 4G10, PY100, PYKD1, 13F9 and one polyclonal antiserum) were evaluated with respect to their capability to enrich P-Tyr proteins from cell extracts of the K562 leukemia cell line. The enrichment resulted in the detection of a group of proteins that potentially were tyrosine-phosphorylated (putative P-Tyr proteins). High accuracy identification of actual P-Tyr sites were performed using a highly selective and sensitive liquid chromatography Fourier transform mass spectrometer (LC-FTMS) setup with complementary collision activated dissociation (CAD) and electron capture dissociation (ECD) fragmentations. 4G10 and PY100 antibodies recognized the greatest number of putative P-Tyr proteins in initial screening experiments and were therefore further evaluated and compared in immunoaffinity enrichment of both P-Tyr proteins and peptides. Using the 4G10 antibody for enrichment of proteins, we identified 459 putative P-Tyr proteins by MS. Out of these proteins, 12 were directly verified as P-Tyr proteins by MS analysis of the actual site. Using the PY100 antibody for enrichment of peptides, we detected 67 P-Tyr peptides (sites) and 89 putative P-Tyr proteins. Generally, enrichment at the peptide level made it difficult to reliably determine the identity of the proteins. In contrast, protein identification following immunoaffinity enrichment at the protein level gave greater sequence coverage and thus a higher confidence in the protein identification. By combining all available information, 40 proteins were identified as true P-Tyr proteins from the K562 cell line. In conclusion, this study showed that a combination of immunoaffinity enrichment using multiple antibodies of both intact and digested proteins in parallel experiments is required for best possible coverage of all possible P-Tyr proteins in a sample.

Resveratrol regulates the expression of LXR-alpha in human macrophages.

The naturally occurring polyphenol resveratrol has been associated with the beneficial effects of red wine consumption on cardiovascular disease and shown to inhibit atherosclerosis in animal models. To determine if resveratrol affects the expression of genes that control lipid homeostasis in human macrophages, we measured expression changes in the LXR-alpha pathway, crucial to cholesterol efflux, and in genes that mediate lipoprotein uptake. Resveratrol treatment of THP-1 macrophages induced LXR-alpha at mRNA and protein levels. Increased recruitment of RNA polymerase II to the LXR-alpha promoter suggested that up-regulation was at least partly mediated by transcriptional mechanisms. Resveratrol also induced LXR-alpha in human monocyte-derived macrophages together with elevated ABCA1 and ABCG1 mRNA levels. Moreover, resveratrol repressed the expression of the lipid uptake genes LPL and SR-AII. The ability of resveratrol to modulate expression of the genes involved in lipid uptake and efflux suggests that polyphenols can potentially limit cholesterol accumulation in human macrophages.