Formation of Benign Tumours by Stem Cell Misregulation

Our tissues usually have just the right number of cells to optimally fulfil their function. Not enough cells within a tissue can lead to dysfunction, while too many cells result in a tumour. Yet, how this homeostatic balance is maintained remains poorly defined. Most differentiated cells within tissues have a finite lifespan and need to be replaced at a corresponding pace to maintain tissue homeostasis. These new differentiated cells are generated by proliferation of the stem/progenitor cells that serve the tissue. Work in simple invertebrates clearly suggests stem cells respond to at least two types of signals: niche signaling and growth factors. Niche signals promote the undifferentiated state by preventing differentiation, and thus allow for stem cell self-renewal. Growth factor sources comprise a systemic input reflecting the animal’s nutritional status, and a localized, homeostatic feedback from the tissue that the stem cells serve. That homeostatic signal couples stem cell proliferation rates to the tissue’s need for new differentiated cells. Evidence from simple organisms suggests two types of benign tumours can arise from deregulation of either niche or homeostatic signaling. Namely, constitutive niche signaling promotes the formation of undifferentiated “stem cell” tumours, while defective homeostatic signaling leads to the formation of differentiated tumours. We propose that these principles may be conserved and underlie benign tumour formation in humans, while benign tumours can evolve into cancer.

The Role of Altered Mitochondrial Metabolism in Thyroid Cancer Development and Mitochondria-Targeted Thyroid Cancer Treatment

Thyroid cancer (TC) is the most common type of endocrine malignancy. Tumour formation, progression, and metastasis greatly depend on the efficacy of mitochondria—primarily, the regulation of mitochondria-mediated apoptosis, Ca2+ homeostasis, dynamics, energy production, and associated reactive oxygen species generation. Recent studies have successfully confirmed the mitochondrial aetiology of thyroid carcinogenesis. In this review, we focus on the recent progress in understanding the molecular mechanisms of thyroid cancer relating to altered mitochondrial metabolism. We also discuss the repurposing of known drugs and the induction of mitochondria-mediated apoptosis as a new trend in the development of anti-TC therapy.

Engraftment of allotransplantated tumour cells in adult rag2 mutant Xenopus tropicalis

Modelling human genetic diseases and cancer in lab animals has been greatly aided by the emergence of genetic engineering tools such as TALENs and CRISPR/Cas9. We have previously demonstrated the ease with which genetically engineered Xenopus models (GEXM) can be generated. This included the induction of autochthonous tumour formation by injection of early embryos with Cas9 recombinant protein loaded with sgRNAs targeting multiple tumour suppressor genes. What has been lacking so far is the possibility to propagate the induced cancers via transplantation. In this paper we describe the generation of a rag2-/- knock-out line in Xenopus tropicalis that is deficient in functional T- and B-cells. This line was validated by means of an allografting experiment with a primary tp53-/- donor tumour. In addition, we optimized available protocols for sub-lethal gamma irradiation of X. tropicalis froglets. Irradiated animals also allowed stable, albeit transient, engraftment of transplanted tp53-/- tumour cells. The novel X. tropicalis rag2-/- line and the irradiated wild type froglets will further expand the experimental toolbox in this diploid amphibian, and help to establish it as a versatile and relevant model for exploring human cancer.

Use of a new mouse schwannoma tumour model to monitor changes in peripheral nerve morphology in Merlin null Schwann cells

Aims Our lab is interested in signals that trigger schwannoma tumour formation and we have previously shown that peripheral nerve injury triggers tumour formation in nerves with Schwann cell-specific loss of the Merlin (NF2) tumour suppressor. The Ras/Raf/MAPK/ERK pathway activity in myelinating Schwann cells is involved in nerve regeneration, causing demyelination and recruitment of inflammatory cells in areas of nerve damage, as well as dedifferentiation of myelinating Schwann cells into a repair-competent state. We have used a mouse model expressing a tamoxifen-inducible Raf-Kinase estrogen receptor fusion protein (Raf-TR) in myelinating Schwann cells of the PNS in either a control wild-type Merlin or Merlin-null background. This allows us to determine the effects of an injury-like signal in Schwann cells and its role in generating schwannoma tumour development. We present here a detailed analysis of the proliferation of Schwann cells within the nerve and morphological changes in PNS structure following Raf-TR activation. Method The P0-promotor driving the Raf-TR transgene is active in myelinating Schwann cells but inactive in the non-myelinating population, allowing specific targeting of the myelinating Schwann cell population. In addition to the Raf-TR gene, the mice exhibit a separate P0-promotor controlled Cre floxed NF2 gene which undergoes Cre-mediated recombinase at embryonic day 13.5 causing NF2 knockout in all developing Schwann cells. Mice aged between 4-6 weeks received intraperitoneal injections of either 2mg Tamoxifen or oil vehicle for 5 consecutive days and were then studied at either 10 or 21 days post-first injection. The peripheral nervous system of the mice was studied with fluorescent immuno-histochemistry staining, semithin sections and transmission electron microscopy (TEM) on sciatic nerves and dorsal root ganglia (DRG). Results Activation of the Ras/Raf/MAPK/ERK pathway in NF2 null Schwann cells led to higher rates of proliferation within sciatic nerves at 10d post-tamoxifen injections. At both 10d and 21d Raf-TR+ NF2-null mice sciatic nerve fascicles were visibly larger with significantly more cell bodies present than controls, however at 21d the rate of proliferation had reduced. In the DRG, proliferation was higher in Raf-TR+ NF2-null mice compared to controls, with proliferation remaining high at 21 days. Quantitative imaging of peripheral nerve semi-thins analysed to date showed no significant difference in the number of myelin rings present in the fascicles between different genotypes. Additionally, dual immuno-histochemistry staining with Myelin Basic Protein and EdU, markers for myelin and proliferation respectively, appeared to show proliferation in the non-myelinating Schwann cell population. Results from staining with other cell markers will also be presented, as well as a detailed analysis of nerve structure using TEM. Conclusion While developmental myelination of Merlin-null Schwann cells appears largely normal, the reaction of Merlin-null Schwann cells in the nerve to an injury signal (activation of the Raf-TR) is remarkably different from those of control nerves. The high levels of proliferation in Merlin-null Schwann cells may be indicative of a higher tumorigenesis potential. While the proliferation of Merlin-null cells does reduce over time in the sciatic nerve, further experiments are now testing whether there may be ongoing tumour growth at other locations in the nervous system that are associated with NF2 tumours in human patients.

Medulloblastoma in Adulthood

Defined as a tumour with increased malignancy potential in childhood, medulloblastoma was first reported in the literature by Percival Bailey and Harvey Cushing in 1925. Scientific studies over the years have shown that this type of tumour represents about 20% of all intracranial tumours encountered in childhood, their percentage decreasing with advancing age. The genetic factor plays an important part in the appearance of medulloblastoma; there are certain diseases, in the patient’s history, that can be associated with this type of tumour. Here, we can specify Turcot syndrome (an autosomal recessive disease, rarely encountered) or basal cell carcinoma syndrome. This article presents the case of a young patient (41-year-old) suffering from a cerebellar tumour formation that turned out to be, after histopathological examination, a medulloblastoma. In practice we can find several types of medulloblastoma (desmoplastic or nodular, anaplastic, classical or undifferentiated). In what follows I will try to highlight a few aspects of a classic medulloblastoma.

Gene Duplication and Gene Fusion Are Important Drivers of Tumourigenesis during Cancer Evolution

Chromosomal rearrangement and genome instability are common features of cancer cells in human. Consequently, gene duplication and gene fusion events are frequently observed in human malignancies and many of the products of these events are pathogenic, representing significant drivers of tumourigenesis and cancer evolution. In certain subsets of cancers duplicated and fused genes appear to be essential for initiation of tumour formation, and some even have the capability of transforming normal cells, highlighting the importance of understanding the events that result in their formation. The mechanisms that drive gene duplication and fusion are unregulated in cancer and they facilitate rapid evolution by selective forces akin to Darwinian survival of the fittest on a cellular level. In this review, we examine current knowledge of the landscape and prevalence of gene duplication and gene fusion in human cancers.

Cooperation between liver-specific mutations of pten and tp53 genetically induces hepatocarcinogenesis in zebrafish

Background Liver cancer, mainly hepatocellular carcinoma, is one of the deadliest cancers worldwide and has a poor prognosis due to insufficient understanding of hepatocarcinogenesis. Previous studies have revealed that the mutations in PTEN and TP53 are the two most common genetic events in hepatocarcinogenesis. Here, we illustrated the crosstalk between aberrant Pten and Tp53 pathways during hepatocarcinogenesis in zebrafish. Methods We used the CRISPR/Cas9 system to establish several transgenic zebrafish lines with single or double tissue-specific mutations of pten and tp53 to genetically induce liver tumorigenesis. Next, the morphological and histological determination were performed to investigate the roles of Pten and Tp53 signalling pathways in hepatocarcinogenesis in zebrafish. Results We demonstrated that Pten loss alone induces hepatocarcinogenesis with only low efficiency, whereas single mutation of tp53 failed to induce tumour formation in liver tissue in zebrafish. Moreover, zebrafish with double mutations of pten and tp53 exhibits a much higher tumour incidence, higher-grade histology, and a shorter survival time than single-mutant zebrafish, indicating that these two signalling pathways play important roles in dynamic biological events critical for the initiation and progression of hepatocarcinogenesis in zebrafish. Further histological and pathological analyses showed significant similarity between the tumours generated from liver tissues of zebrafish and humans. Furthermore, the treatment with MK-2206, a specific Akt inhibitor, effectively suppressed hepatocarcinogenesis in zebrafish. Conclusion Our findings will offer a preclinical animal model for genetically investigating hepatocarcinogenesis and provide a useful platform for high-throughput anticancer drug screening.

Tumour Suppressor Parafibromin/Hyrax Governs Cell Polarity and Centrosome Assembly in Neural Stem Cells

Neural stem cells (NSCs) divide asymmetrically to balance their self-renewal and differentiation. The imbalance can lead to NSC overgrowth and tumour formation. The function of Parafibromin, a conserved tumour suppressor, in the nervous system is not established. Here, we demonstrate that Drosophila Parafibromin/Hyrax (Hyx) inhibits NSC overgrowth by governing the cell polarity. Hyx is essential for the apicobasal polarity by localizing both apical and basal proteins asymmetrically in NSCs. hyx loss results in the symmetric division of NSCs, leading to the formation of supernumerary NSCs in the larval brain. Human Parafibromin fully rescues NSC overgrowth and cell polarity defects in Drosophila hyx mutant brains. Hyx plays a novel role in maintaining interphase microtubule-organizing center and mitotic spindle formation in NSCs. Hyx is required for the proper localization of a key centrosomal protein Polo and microtubule-binding proteins Msps and D-TACC in dividing NSCs. This study discovers that Hyx has a brain tumour suppressor-like function and maintains NSC polarity by regulating centrosome function and microtubule growth. The new paradigm that Parafibromin orchestrates cell polarity and centrosomal assembly may be relevant to Parafibromin/HRPT2-associated cancers.