Finance Committee - Three-hundred-and-sixty-first Meeting

RT-qPCR primers and probes used. Quantitative real-time PCR assay targets are specified, together with their IDs, primer and probe sequences are shown together with optimal concentrations to be used in the reaction. (DOCX 21 kb

TRIM28 and β-actin identified via nanobody-based reverse proteomics approach as possible human glioblastoma biomarkers.

Malignant gliomas are among the rarest brain tumours, and they have the worst prognosis. Grade IV astrocytoma, known as glioblastoma multiforme (GBM), is a highly lethal disease where the standard therapies of surgery, followed by radiation and chemotherapy, cannot significantly prolong the life expectancy of the patients. Tumour recurrence shows more aggressive form compared to the primary tumour, and results in patient survival from 12 to 15 months only. Although still controversial, the cancer stem cell hypothesis postulates that cancer stem cells are responsible for early relapse of the disease after surgical intervention due to their high resistance to therapy. Alternative strategies for GBM therapy are thus urgently needed. Nanobodies are single-domain antigen-binding fragments of heavy-chain antibodies, and together with classical antibodies, they are part of the camelid immune system. Nanobodies are small and stable, and they share a high degree of sequence identity to the human heavy chain variable domain, and these characteristics offer them advantages over classical antibodies or antibody fragments. We first immunised an alpaca with a human GBM stem-like cell line prepared from primary GBM cultures. Next, a nanobody library was constructed in a phage-display vector. Using nanobody phage-display technology, we selected specific GBM stem-like cell binders through a number of affinity selections, using whole cell protein extracts and membrane protein-enriched extracts from eight different GBM patients, and membrane protein-enriched extracts from two established GBM stem-like cell lines (NCH644 and NCH421K cells). After the enrichment, periplasmic extract ELISA was used to screen for specific clones. These nanobody clones were recloned into the pHEN6 vector, expressed in Escherichia coli WK6, and purified using immobilised metal affinity chromatography and size-exclusion chromatography. Specific nanobody:antigen pairs were obtained and mass spectrometry analysis revealed two proteins, TRIM28 and β-actin, that were up-regulated in the GBM stem-like cells compared to the controls

Schematic presentation of the whole workflow.

<p>1. Material preparation – expanding a GBM cell line, laminin grown and enriched in stem-like cells, 2. Llama immunization with whole GBM cells, 3. Construction of a nanobody library, 4. Phage display cycle – enrichment of antigen specific nanobodies on various biological samples (whole protein extract from GBM tissues, membrane protein-enriched fractions from GBM tissues and GBM stem-like cell lines), 5. ELISA - selection of GBM specific nanobodies, 6. Nanobody production – large scale production and purification of specific nanobodies, 7. Nanobody:antigen pairs – immobilizing the nanobodies and binding to the corresponding antigens, 8. Antigen identification by mass spectrometry, 9. Antigen validation by Western blot. See Materials and methods for additional experimental details.</p

Sequences of the nanobodies that were chosen for the large-scale production.

<p>The amino acid sequence of the CDR3 regions of the nanobodies is given in alphabetic order.</p

Schematic presentation of the structure of TRIM28.

<p>The conserved RBCC motif is present at the N-terminal domain; the variable C-domain includes the PHD and BROMO domains. Image adapted from Hatakeyama <i>et al</i>. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0113688#pone.0113688-Hatakeyama1" target="_blank">[45]</a>. Author's approval was obtained for the use of this image; original image is given in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0113688#pone.0113688.s002" target="_blank">Figure S2</a>.</p

Antigen validation.

<p>Western blot membrane after probing with a monoclonal anti-GAPDH antibody (36 kDa band) used as an internal control for amount of protein loaded in each lane, a monoclonal anti-β-actin antibody (48 kDa band) and monoclonal anti-TRIM28 antibody (100 kDa band). Samples: GSCm – membrane protein-enriched extract isolated from GBM stem-like cell lines; GBMm – membrane protein-enriched extract isolated from GBM tissues; NBTm – membrane protein-enriched extract isolated from human brain samples; GSCc – cytosolic/nuclear protein fraction isolated from GBM stem-like cell lines; GBMc – cytosolic/nuclear protein fraction isolated from GBM tissues; NBTc – cytosolic/nuclear protein fraction isolated from human brain samples; GBMw – whole protein extract from GBM tissues; NBTw – whole protein extract from human brain samples.</p

Relative band intensities of antigens validated with Western blot.

<p>The relative band intentisy of the antigens, TRIM28 and β-actin, was calculated as the ratio between arbitrary units of the band of the antigen and the arbitrary units of the band of the internal control, GAPDH [AU(antigen)/AU(GAPDH)]. Samples: GSCc – cytosolic/nuclear protein fraction isolated from GBM stem-like cell lines; GBMc – cytosolic/nuclear protein fraction isolated from GBM tissues; NBTc – cytosolic/nuclear protein fraction isolated from human brain samples.</p