In 1997, Danen-Van Oorschot et al. described for the first time that apoptin, a protein encoded by an avian virus, induces p53-independent apoptosis in a tumor-specific way. Various pre-clinical... Show moreIn 1997, Danen-Van Oorschot et al. described for the first time that apoptin, a protein encoded by an avian virus, induces p53-independent apoptosis in a tumor-specific way. Various pre-clinical studies in animal tumor models have demonstrated apoptin as a safe and efficient anti-tumor agent. In tumor cells, apoptin is imported into the nucleus prior to the induction of apoptosis and regulated by a kinase activity specifically present in cancer cells. In this thesis, several studies have been carried out to reveal the novel aspects of the molecular pathways underlying the transformation-related apoptosis induction by the viral protein apoptin. Show less
The major targets in Systemic lupus erythematosus (SLE, a systemic autoimmune disease) are nuclear components (DNA, histones, ribonucleoproteins), which are mainly derived from dying cells ... Show moreThe major targets in Systemic lupus erythematosus (SLE, a systemic autoimmune disease) are nuclear components (DNA, histones, ribonucleoproteins), which are mainly derived from dying cells (apoptotic and necrotic cells). Defective clearance of dying cells by phagocytes may lead to the breakdown of peripheral tolerance and initiation of autoimmune SLE. I have investigated the role of the innate immune system in the processing of dying cells and its immunological consequences. I found that a subset of macrophages driven by M-CSF have intrinsic anti-inflammatory properties and are potent phagocytes that have the unique capacity to preferentially bind and ingest early apoptotic cells in a silent manner. I also identified that human peritoneal macrophages freshly isolated from patients on peritoneal dialysis resemble functionally the in vitro-generated M-CSF-driven macrophages. I further showed that the anti-inflammatory and pro-inflammatory macrophages co-exist but can re-differentiate towards opposing phenotype depending on the local cytokine environment. Next to the phagocyte system, I investigated the role of components of the innate immune system in the processing of dying cells. I found that one of the complement regulators called properdin, binds predominantly to late apoptotic and necrotic cells independently of C3b, resulting alternative pathway complement activation. Show less
The current thesis discusses the use of molecular and biological tumor markers to predict clinical outcome. By studying several key processes in the develepment of cancer as regulation of cell... Show moreThe current thesis discusses the use of molecular and biological tumor markers to predict clinical outcome. By studying several key processes in the develepment of cancer as regulation of cell motility (non-receptor protein tyrosin adesion kinases, FAK, Src and paxillin, Apoptosis (caspase-3 activity and M30 expression) and regulation of cell growth (COX-2 expression). In addition the use of selective COX-2 inhibitors for the treatment of colorectal cancer liver metastases is investigated and discussed. The main outcomes of the thesis are that combined FAK/Src immunohistochemical expression is predictive of tumor recurrence in colorectal cancer, but is not overexpressed in liver metastases. Increased tumor cell apoptosis can have a positive or a negative impact on survival and local recurrence, depending on the location of the tumor in the large bowel . In rectal cancer caspase-3 activity can be used to preoperatively select patients who will not benefit from radiation therapy. COX-2 expression in rectal cancer is only of prognostic significance in irradiated rectal cancer patients, not in non-irradiated. Liver metastases in an animal model show deminished growth in the abcence of COX-2 expression and prostaglandin production. Show less
The development of multicellular organisms involves an important balance between cell growth, cell division and cell death. In animals, programmed cell death (PCD) plays a key role by forming and... Show moreThe development of multicellular organisms involves an important balance between cell growth, cell division and cell death. In animals, programmed cell death (PCD) plays a key role by forming and deleting structures, controlling cell numbers and eliminating abnormal damaged cells. Caspases were found to be the key executioner of the cell suicide pathway. In plants, PCD plays an important role in development and in the responses to pathogens and abiotic stresses. Some common features of PCD were found to be conserved in both plants and animals (cytoplasm shrinkage, cytochrome c leakage out of mitochondria, chromatin condensation, altered nuclear morphology, DNA fragmentation in large fragments and DNA laddering). This indicates that a similar apoptotic machinery may be present in plants. After the elucidation of the complete sequences of Arabidopsis and rice, it has become clear that no genes for the caspases are present in plants. In this thesis, three model systems are described to determine the existence of caspase-like activities in plants during PCD. The first model used is a T-DNA integration arabidopsis mutant that shows necrotic spots on its leaves. The second model used is barley, during the transition from multicellular structures to globular embryos during androgenesis. The third model used was an artificial model of rice suspension cells with heat-shock as a PCD inducer. In these models, PCD was described and caspase-like activity was measured. In addition, the development and implementation of the protocol to purify plant caspase-3 like activity is described. Show less
Head and Neck Paragangliomas (HNP) are hypervascular tumours characterised by a slow growth pattern and a strong hereditary context that originate from the neural crest derived paraganglia, which... Show moreHead and Neck Paragangliomas (HNP) are hypervascular tumours characterised by a slow growth pattern and a strong hereditary context that originate from the neural crest derived paraganglia, which are associated with the autonomous nervous system and are situated at several locations in the head and neck region. Inactivating mutations in subunits of complex II (SDH) of the mitochondrial respiratory chain are responsible for hereditary tumours and have lead to a novel concept of mitochondrial tumoursupressor-genes and further insight in the intricate association of cellular oxygen sensing mechanisms and (pseudo)-hypoxia as environmental risk factors. However, further characterisation of the tumour biology is warranted for better understanding of the natural behaviour of HNP and possible identification clinicopathological parameters that could aid the clinician in his treatment decisions. In this thesis several studies on the molcular pathology of HNP are discussed including genotype-fenotype relations, the role of bFGF in tumourgenisis, the interplay between proliferation, cell cycle activity and apoptosis, and the nature of sustentacular cells in these apparent biphasic tumours. Additionally, in a clincal study the prevalence of synchronic or metachronic pheochromocytomas in patients with SDHD-linked HNP was determined. Show less
Cholesteatoma is a benign, gradually expanding destructive epithelial lesion of the temporal bone, often accompanied with inflammation. The complications can be severe, e.g., destruction of the... Show moreCholesteatoma is a benign, gradually expanding destructive epithelial lesion of the temporal bone, often accompanied with inflammation. The complications can be severe, e.g., destruction of the ossicular chain and otic capsule with consecutive hearing loss. Several hypotheses for the pathogenesis of human cholesteatoma have been proposed but are still controversial. In this thesis, protein signaling pathways were investigated which are involved in different aspects of cholesteatoma pathogenesis, such as hyperproliferation, aberrant differentiation, and extra-cellular matrix deposition. In cholesteatoma epithelium increased expressions of those proteins were found which are involved in proliferation (Ki-67), cell cycle arrest (p53, p21), early terminal differentiation (involucrin) and survival (pAKT). The proteins of which the expressions were decreased were those concerning late terminal differentiation (filaggrin) and apoptosis (active caspase 3). Moreover, increased activation of MAPK- and its association with TGF_ cellular signaling cascades were demonstrated. In cholesteatoma stroma, increased extracellular matrix deposition, visualized by accumulation of EDA-Fibronectin, was present. These results were placed in the context of the interconnected signaling processes of wound healing. Concluding: cholesteatoma behaves as a chronic wound in which a persistent inflammation appears to be a contributing factor to its chronicity. Research into pharmacological interventions aimed at control of inflammation is recommended. Show less
