Year: 2015
Type: dissertation
Abstract: Exosomes are nanometer-sized vesicles (40-100 nm) secreted by various cells types.They are generated from late endosomes/multivesicular bodies (MVBs) and are released into extracellular space upon the fusion of MVBs outer membrane with plasma membrane.Exosomes exert a broad range of biological effects by transferring different contents (such as DNA, RNA, proteins and lipids).In particular, multiple signalling molecules (such as Wnt proteins) are carried in exosomes which promote tumor aggressiveness.Transforming growth factor-β (TGF-β) is a key player in various biological processes.TGF-β signalling is tightly regulated by multiple molecules at each step of the signalling cascade.Dysregulation of TGF-β signalling has been implicated in the pathogenesis of human diseases, including cancer.TGF-β can signal not only via linear signalling cascade but also through crosstalk with other pathways.Importantly, TGF-β and Ras signallings are found to act in synergy to promote malignant progression.Ras enhances TGF-β signalling by suppressing the SPRY domain and SOCS Box containing protein 1 (SPSB1), a negative regulator of TGF-β type II receptor (TβRII).However, the underlying molecular mechanism is controversial because Ras does not change the poly-ubiquitination levels of SPSB1.Active TGF-β has been discovered in exosomes.Exosomal TGF-β is shown to activate Smad-dependent signalling in recipient cells and drive fibroblast to myofibroblast differentiation.However, it is not clear how exosomes are involved in the regulation of TGFβ signalling.In particular, how exosomal TGF-β may differ from free ligand TGF-β in exerting their biological functions is yet to be answered.Moreover, SPSB1 is detectable in exosomes from Ras-transformed cells, raising the possibility that exosomes participate in Ras-induced up-regulation of TGF-β signalling by exporting SPSB1 from the cell.This thesis demonstrated that highly metastatic tumor cell lines secreted higher levels of exosomal TGF-β in comparison with non-/low-metastatic tumor cell lines, suggesting the potential of exosomal TGF-β as a biomarker for metastatic cancer.Moreover, exosomal TGFβ activated TGF-β signalling in TGF-β receptor-defective cells.This observation will cause a re-evaluation of TGF-β signalling"s role in tumorigenesis of human colon cancer harbouring TβRII inactivating mutation.Importantly, ligand traps were inefficient in blocking exosomal TGF-β-mediated TGF-β signalling.Consequently, strategies have to be developed to target exosomal TGF-β.BMP Bone morphogenetic protein CAF Carcinoma/cancer-associated fibroblasts DMA Dimethyl amiloride DMEM Dulbecco"s modified Eagle"s medium ECM Extracellular matrix EGF Epidermal growth factor EGFR Epidermal growth factor receptor ELISA Enzyme-linked immunosorbent EMT Epithelial-mesenchymal transition ERK Extracellular signal-regulated kinase ESCRT Endosomal sorting complex required for transport FCS Fetal calf serum GAP GTPase-activating protein GEF Guanine exchange factor GDP Guanosine diphosphate GDF Growth and differentiation factors GTP Guanosine triphosphate GTPase Guanosine triphosphatase HGF Hepatocyte growth factor HIF1α Hypoxia-inducible factor-1α ILV Intraluminal vesicle kDa kilo Dalton LAP TGF-β latency associated protein LLC Large latent TGF-β complex LMP1 Latent membrane protein 1 LTBP Latent TGFβ-binding protein MAPK Mitogen-activated protein kinase MDCK Madin-Darby canine kidney MMP Matrix metalloproteinases MVB Multivesicular body PBS Phosphate-buffered saline PI3K Phosphatidylinositol (PI) 3-kinase PTEN Phosphatase and tensin homologue Ras Rat sarcoma virus SDS-PAGE Sodium dodecyl sulfate-polyacrylamide gel electrophoresis SLC SLC small latent TGF-β complex Smad Sma and Mad related protein SOCS Suppressor of cytokine signalling SPRY Sequence repeat in the dual-specificity kinase splA and ryanodine SPSB1 SPRY domain and SOCS Box containing protein 1 sTβRII-Fc Soluble TGF-β receptor II-Fc TEM Transmission electron microscopy TGF-β Transforming growth factor-β TβRI Transforming growth factor-β type I receptor TβRII Transforming growth factor-β type II receptor TNF-α Tumor necrosis factor-α VEGF Vascular endothelial growth factorCancer exosomes transduce receptor-independent TGF-β signalling and evade ligand trapping therapy
Author: Lin Liu
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2257172172