A DNA-PK phosphorylation site on MET regulates its signaling interface with the DNA damage response.

The DNA damage response (DDR) is intertwined with signaling pathways downstream of oncogenic receptor tyrosine kinases (RTKs). To drive research into the application of targeted therapies as radiosensitizers, a better understanding of this molecular crosstalk is necessary. We present here the characterization of a previously unreported MET RTK phosphosite, Serine 1016 (S1016) that represents a potential DDR-MET interface. MET S1016 phosphorylation increases in response to irradiation and is mainly targeted by DNA-dependent protein kinase (DNA-PK). Phosphoproteomics unveils an impact of the S1016A substitution on the overall long-term cell cycle regulation following DNA damage. Accordingly, the abrogation of this phosphosite strongly perturbs the phosphorylation of proteins involved in the cell cycle and formation of the mitotic spindle, enabling cells to bypass a G2 arrest upon irradiation and leading to the entry into mitosis despite compromised genome integrity. This results in the formation of abnormal mitotic spindles and a lower proliferation rate. Altogether, the current data uncover a novel signaling mechanism through which the DDR uses a growth factor receptor system for regulating and maintaining genome stability.

An oncogene addiction phosphorylation signature and its derived scores inform tumor responsiveness to targeted therapies.

PURPOSE: Oncogene addiction provides important therapeutic opportunities for precision oncology treatment strategies. To date the cellular circuitries associated with driving oncoproteins, which eventually establish the phenotypic manifestation of oncogene addiction, remain largely unexplored. Data suggest the DNA damage response (DDR) as a central signaling network that intersects with pathways associated with deregulated addicting oncoproteins with kinase activity in cancer cells. EXPERIMENTAL: DESIGN: We employed a targeted mass spectrometry approach to systematically explore alterations in 116 phosphosites related to oncogene signaling and its intersection with the DDR following inhibition of the addicting oncogene alone or in combination with irradiation in MET-, EGFR-, ALK- or BRAF (V600)-positive cancer models. An NSCLC tissue pipeline combining patient-derived xenografts (PDXs) and ex vivo patient organotypic cultures has been established for treatment responsiveness assessment. RESULTS: We identified an 'oncogene addiction phosphorylation signature' (OAPS) consisting of 8 protein phosphorylations (ACLY S455, IF4B S422, IF4G1 S1231, LIMA1 S490, MYCN S62, NCBP1 S22, P3C2A S259 and TERF2 S365) that are significantly suppressed upon targeted oncogene inhibition solely in addicted cell line models and patient tissues. We show that the OAPS is present in patient tissues and the OAPS-derived score strongly correlates with the ex vivo responses to targeted treatments. CONCLUSIONS: We propose a score derived from OAPS as a quantitative measure to evaluate oncogene addiction of cancer cell samples. This work underlines the importance of protein phosphorylation assessment for patient stratification in precision oncology and corresponding identification of tumor subtypes sensitive to inhibition of a particular oncogene.

Quantitative measures of bone shape, cartilage morphometry and joint alignment are associated with disease in an ACLT and MMx rat model of osteoarthritis.

Multi-scale, subject-specific quantitative methods to characterize and monitor osteoarthritis in animal models and therapeutic treatments could help reveal causal relationships in disease development and distinguish treatment strategies. In this work, we demonstrate a reproducible and sensitive quantitative image analysis to characterize bone, cartilage and joint measures describing a rat model of post-traumatic osteoarthritis. Eleven 3-month-old male Wistar rats underwent medial anterior cruciate ligament (ACL) transection and medial meniscectomy on the right knee to destabilise the right tibiofemoral joint. They were sacrificed 6 weeks post-surgery and a silicon-based micro-bead contrast agent was injected in the joint space, before scanning with micro-computed tomography (microCT). Subsequently, 3D quantitative morphometric analysis (QMA), previously developed for rabbit joints, was performed. This included cartilage, subchondral cortical and epiphyseal bone measures, as well as novel tibiofemoral joint metrics. Semi-quantitative evaluation was performed on matching two-dimensional (2D) histology and microCT images. Reproducibility of the QMA was tested on eleven age-matched additional joints. The results indicate the QMA method is accurate and reproducible and that microCT-derived cartilage measurements are valid for the analysis of rat joints. The pathologic changes caused by transection of the ACL and medial meniscectomy were reflected in measurements of bone shape, cartilage morphology, and joint alignment. Furthermore, we were able to identify model-specific predictive parameters based on morphometric parameters measured with the QMA.

Targeting the MET Receptor Tyrosine Kinase as a Strategy for Radiosensitization in Locoregionally Advanced Head and Neck Squamous Cell Carcinoma.

Radiotherapy (RT) along with surgery is the mainstay of treatment in head and neck squamous cell carcinoma (HNSCC). Radioresistance represents a major source of treatment failure, underlining the urgent necessity to explore and implement effective radiosensitization strategies. The MET receptor widely participates in the acquisition and maintenance of an aggressive phenotype in HNSCC and modulates the DNA damage response following ionizing radiation (IR). Here, we assessed MET expression and mutation status in primary and metastatic lesions within a cohort of patients with advanced HNSCC. Moreover, we investigated the radiosensitization potential of the MET inhibitor tepotinib in a panel of cell lines, in vitro and in vivo, as well as in ex vivo patient-derived organotypic tissue cultures (OTC). MET was highly expressed in 62.4% of primary tumors and in 53.6% of lymph node metastases (LNM), and in 6 of 9 evaluated cell lines. MET expression in primaries and LNMs was significantly associated with decreased disease control in univariate survival analyses. Tepotinib abrogated MET phosphorylation and to distinct extent MET downstream signaling. Pretreatment with tepotinib resulted in variable radiosensitization, enhanced DNA damage, cell death, and G2-M-phase arrest. Combination of tepotinib with IR led to significant radiosensitization in one of two tested in vivo models. OTCs revealed differential patterns of response toward tepotinib, irradiation, and combination of both modalities. The molecular basis of tepotinib-mediated radiosensitization was studied by a CyTOF-based single-cell mass cytometry approach, which uncovered that MET inhibition modulated PI3K activity in cells radiosensitized by tepotinib but not in the resistant ones.

Identification of a MET-eIF4G1 translational regulation axis that controls HIF-1α levels under hypoxia.

Poor oxygenation is a common hallmark of solid cancers that strongly associates with aggressive tumor progression and treatment resistance. While a hypoxia-inducible factor 1α (HIF-1α)-associated transcriptional overexpression of the hepatocyte growth factor (HGF) receptor tyrosine kinase (RTK) MET has been previously documented, any regulation of the HIF-1α system through MET downstream signaling in hypoxic tumors has not been yet described. By using MET-driven in vitro as well as ex vivo tumor organotypic fresh tissue models we report that MET targeting results in depletion of HIF-1α and its various downstream targets. Mechanistically, we provide evidence that MET regulates HIF-1α levels through a protein translation mechanism that relies on phosphorylation modulation of the eukaryotic initiation factor 4G1 (eIF4G1) on serine 1232 (Ser-1232). Targeted phosphoproteomics data demonstrate a significant drop in eIF4G1 Ser-1232 phosphorylation following MET targeting, which is linked to an increased affinity between eIF4G1 and eIF4E. Since phosphorylation of eIF4G1 on Ser-1232 is largely mediated through mitogen-activated protein kinase (MAPK), we show that expression of a constitutively active K-RAS variant is sufficient to abrogate the inhibitory effect of MET targeting on the HIF-1α pathway with subsequent resistance of tumor cells to MET targeting under hypoxic conditions. Analysis of The Cancer Genome Atlas data demonstrates frequent co-expression of MET, HIF-1α and eIF4G1 in various solid tumors and its impact on disease-free survival of non-small cell lung cancer patients. Clinical relevance of the MET-eIF4G1-HIF-1α pathway is further supported by a co-occurrence of their expression in common tumor regions of individual lung cancer patients.

Three-Dimensional Quantitative Morphometric Analysis (QMA) for In Situ Joint and Tissue Assessment of Osteoarthritis in a Preclinical Rabbit Disease Model.

This work utilises advances in multi-tissue imaging, and incorporates new metrics which define in situ joint changes and individual tissue changes in osteoarthritis (OA). The aims are to (1) demonstrate a protocol for processing intact animal joints for microCT to visualise relevant joint, bone and cartilage structures for understanding OA in a preclinical rabbit model, and (2) introduce a comprehensive three-dimensional (3D) quantitative morphometric analysis (QMA), including an assessment of reproducibility. Sixteen rabbit joints with and without transection of the anterior cruciate ligament were scanned with microCT and contrast agents, and processed for histology. Semi-quantitative evaluation was performed on matching two-dimensional (2D) histology and microCT images. Subsequently, 3D QMA was performed; including measures of cartilage, subchondral cortical and epiphyseal bone, and novel tibio-femoral joint metrics. Reproducibility of the QMA was tested on seven additional joints. A significant correlation was observed in cartilage thickness from matching histology-microCT pairs. The lateral compartment of operated joints had larger joint space width, thicker femoral cartilage and reduced bone volume, while osteophytes could be detected quantitatively. Measures between the in situ tibia and femur indicated an altered loading scenario. High measurement reproducibility was observed for all new parameters; with ICC ranging from 0.754 to 0.998. In conclusion, this study provides a novel 3D QMA to quantify macro and micro tissue measures in the joint of a rabbit OA model. New metrics were established consisting of: an angle to quantitatively measure osteophytes (σ), an angle to indicate erosion between the lateral and medial femoral condyles (ρ), a vector defining altered angulation (λ, α, ß, γ) and a twist angle (τ) measuring instability and tissue degeneration between the femur and tibia, a length measure of joint space width (JSW), and a slope and intercept (m, Χ) of joint contact to demonstrate altered loading with disease progression, as well as traditional bone and cartilage and histo-morphometry measures. We demonstrate correlation of microCT and histology, sensitive discrimination of OA change and robust reproducibility.

S100A1 and S100B expression patterns identify differentiation status of human articular chondrocytes.

Many studies in the field of cell-based cartilage repair have focused on identifying markers associated with the differentiation status of human articular chondrocytes (HAC) that could predict their chondrogenic potency. A previous study from our group showed a correlation between the expression of S100 protein in HAC and their chondrogenic potential. The aims of the current study were to clarify which S100 proteins are associated with HAC differentiation status and to provide an S100-based assay for measuring HAC chondrogenic potential. The expression patterns of S100A1 and S100B were investigated in cartilage and in HAC cultured under conditions promoting dedifferentiation (monolayer culture) or redifferentiation (pellet culture or BMP4 treatment in monolayer culture), using characterized antibodies specifically recognizing S100A1 and S100B, by immunohistochemistry, immunocytochemistry, Western blot, and gene expression analysis. S100A1 and S100B were expressed homogeneously in all cartilage zones, and decreased during dedifferentiation. S100A1, but not S100B, was re-expressed in pellets and co-localized with collagen II. Gene expression analysis revealed concomitant modulation of S100A1, S100B, collagen type II, and aggrecan: down-regulation during monolayer culture and up-regulation upon BMP4 treatment. These results strongly support an association of S100A1, and to a lesser extent S100B, with the HAC differentiated phenotype. To facilitate their potential application, we established an S100A1/B-based flow cytometry assay for accurate assessment of HAC differentiation status. We propose S100A1 and S100B expression as a marker to develop potency assays for cartilage regeneration cell therapies, and as a redifferentiation readout in monolayer cultures aiming to investigate stimuli for chondrogenic induction.

Plasticity of fetal cartilaginous cells.

Tissue-specific stem cells found in adult tissues can participate in the repair process following injury. However, adult tissues, such as articular cartilage and intervertebral disc, have low regeneration capacity, whereas fetal tissues, such as articular cartilage, show high regeneration ability. The presence of fetal stem cells in fetal cartilaginous tissues and their involvement in the regeneration of fetal cartilage is unknown. The aim of the study was to assess the chondrogenic differentiation and the plasticity of fetal cartilaginous cells. We compared the TGF-ß3-induced chondrogenic differentiation of human fetal cells isolated from spine and cartilage tissues to that of human bone marrow stromal cells (BMSC). Stem cell surface markers and adipogenic and osteogenic plasticity of the two fetal cell types were also assessed. TGF-ß3 stimulation of fetal cells cultured in high cell density led to the production of aggrecan, type I and II collagens, and variable levels of type X collagen. Although fetal cells showed the same pattern of surface stem cell markers as BMSCs, both type of fetal cells had lower adipogenic and osteogenic differentiation capacity than BMSCs. Fetal cells from femoral head showed higher adipogenic differentiation than fetal cells from spine. These results show that fetal cells are already differentiated cells and may be a good compromise between stem cells and adult tissue cells for a cell-based therapy.

Isolation and in vitro chondrogenic potential of human foetal spine cells.

Cell therapy for nucleus pulposus (NP) regeneration is an attractive treatment for early disc degeneration as shown by studies using autologous NP cells or stem cells. Another potential source of cells is foetal cells. We investigated the feasibility of isolating foetal cells from human foetal spine tissues and assessed their chondrogenic potential in alginate bead cultures. Histology and immunohistochemistry of foetal tissues showed that the structure and the matrix composition (aggrecan, type I and II collagen) of foetal intervertebral disc (IVD) were similar to adult IVD. Isolated foetal cells were cultured in monolayer in basic media supplemented with 10% Fetal Bovine Serum (FBS) and from each foetal tissue donation, a cell bank of foetal spine cells at passage 2 was established and was composed of around 2000 vials of 5 million cells. Gene expression and immunohistochemistry of foetal spine cells cultured in alginate beads during 28 days showed that cells were able to produce aggrecan and type II collagen and very low level of type I and type X collagen, indicating chondrogenic differentiation. However variability in matrix synthesis was observed between donors. In conclusion, foetal cells could be isolated from human foetal spine tissues and since these cells showed chondrogenic potential, they could be a potential cell source for IVD regeneration.

Consistency and safety of cell banks for research and clinical use: preliminary analysis of fetal skin banks.

Current restrictions for human cell-based therapies have been related to technological limitations with regards to cellular proliferation capacity, maintenance of differentiated phenotype for primary human cell culture, and transmission of communicable diseases. We have seen that cultured primary fetal cells from one organ donation could possibly meet the exigent and stringent technical aspects for development of therapeutic products. We could develop a master cell bank (MCB) of 50 homogenous ampoules of 4-5 million cells each from one fetal organ donation (skin) in short periods of time compared to other primary cell types. Safety tests were performed at all stages of the cell banking. MCB ampoules could create a working cell bank to be used for clinical or research use. Monolayer culture of fetal skin cells had a life span of 12-17 passages, and independent cultures obtained from the same organ donation were consistent for protein concentration (with 1.4-fold maximal difference between cultures) as well as gene expression of MMP-14, MMP-3, TIMP-3, and VEGF (1.4-, 1.9-, 2.1-, and 1.4-fold maximal difference between cultures, respectively). Cell cultures derived from four independent fetal skin donations were consistent for cell growth, protein concentration, and gene expression of MDK, PTN, TGF-beta1, and OPG. As it is the intention that banked primary fetal cells can profit from the potential treatment of hundreds of thousands of patients with only one organ donation, it is imperative to show consistency, tracability, and safety of the process, including donor tissue selection, cell banking, cell testing, and growth of cells in upscaling for the preparation of cell transplantation.