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Cell Biology of Signalling, Membrane Trafficking, Secretion and Growth in Normal and Cancer Cells at Super-Resolution

Male Drosophila accessory gland
Male Drosophila accessory gland

RESEARCH SUMMARY 

During normal development and in adults, cells co-ordinate basic processes such as growth, migration, metabolism, membrane trafficking and secretion by communicating with each other via cell-cell signalling. In cancer, neurodegenerative disorders and metabolic diseases such as diabetes, these communication mechanisms and/or the processes they control are mis-regulated. Our group studies the regulation of these cellular processes in the fruit fly, Drosophila melanogaster. For many years, we have had an interest in insulin-like molecules and how their signalling inside cells (here referred to as insulin signalling) regulates growth, metabolism and physiology at a cell, tissue and whole organism level. We have collaborated with other groups working on human cells to define evolutionarily conserved mechanisms in insulin signalling and function.

This work has highlighted critical links between cell signalling pathways and intracellular membrane trafficking and secretion, which despite their fundamental importance, have been challenging to study because of the limited number of in vivo models available in which membrane-bound compartments inside cells can be analysed in detail using light microscopy.

Over the last few years, we have been developing the male accessory gland in the fly as a unique new model to address this problem, and more particularly the prostate-like secondary cells in this organ, which have extremely large secretory, endosomal and lysosomal compartments. These studies have started to inform our understanding of prostate biology, and allowed us to investigate the unusual molecular mechanisms by which males signal to females during mating to change their physiology and behaviour, and how those mechanisms are modulated by mating and socio-sexual experience. They have also revealed fundamental new insights into several basic cell biological processes, such as the secretion of nanovesicles (or exosomes) as novel signalling moieties, the formation of dense-core secretory granules and the links between different intracelllular compartments and specific cell-cell signalling cascades. This work is relevant to multiple major human diseases, as well as mechanisms of viral and bacterial infection. We have a series of collaborations in place to exploit our findings as they emerge, all the way to the clinic.

Read on to find out more about our multidisciplinary studies and the translational areas in medicine, biodelivery and pest control, which they inform. 

CURRENT RESEARCH PROGRAMME

 

DEVELOPING A NEW MODEL FOR PROSTATE PHYSIOLOGY AND CANCER

 

The majority of men over 50 suffer from benign prostate hyperplasia. Progression to prostate cancer is the second most common cause of cancer death in males. However, animal models for prostate cancer have lagged behind those for many other types of cancer. For example, the mouse prostate is small and differently organised to its human equivalent. In collaboration with Prof Freddie Hamdy from the Nuffield Department of Surgical Sciences in Oxford, we initiated a detailed cell biological and genetic analysis of the Drosophila accessory gland, which like the prostate, secretes a cocktail of proteases and glycoproteins into seminal fluid that activate sperm after mating and affect fertility.

Remarkably, we have found that secondary cells grow selectively with age and after mating in flies, and that a subset of these cells delaminates apically from the epithelium, migrates along the duct of the gland and can ultimately be transferred to females upon mating. This raises the completely novel possibility that some secretory cells in glands involved in sperm activation acquire natural migratory activity to perform their functions. Some of the signals controlling these functions, such as bone morphogenetic proteins, are also required for males to fully reprogramme female behaviour after mating, so she then rejects advances from other males, an event in direct conflict with female interests. BMP signalling and other signalling involved in secondary cell biology is misregulated in prostate cancer. We are now developing models that explain the complex behaviour and functions of secondary cells in flies, and these studies are highlighting further parallels with the prostate.

 

REGULATION AND FUNCTIONS OF EXOSOME SIGNALLING

We have shown that secondary cells secrete membrane-bound vesicles called exosomes, which are transferred to females and play key roles in the reproductive biology of the fly. Similar functions have been proposed for human prostate exosomes through in vitro experiments. Exosomes are formed as minute (50-100 nm) vesicles in the late endosomal multivesicular bodies (MVBs) of cells, and potentially carry signalling proteins, RNA, DNA and lipids, providing them with almost limitless cell reprogramming capability.

The diameter of MVBs and other intracellular compartments in secondary cells, and the sizes of the glandular lumen and female reproductive tract to which exosomes are transferred are all remarkably large. Using the highly versatile cell biological and genetic tools available in flies, we have for the first time in any organism been able to visualize in real-time aspects of exosome biogenesis in living tissue. Our studies have already revealed novel mechanisms by which membrane trafficking and exosomes are regulated by cell-cell signalling, as well as showing that membrane trafficking controls signalling by exosomes, and that secondary cell exosomes are required to reprogramme female behaviour after mating. These findings have far-reaching implications for reproductive biology, and may be relevant to the design of pest control strategies in the future. Furthermore, collaborating with the groups of Deborah Goberdhan (DPAG) and Adrian Harris (WIMM), we have also shown that some of these mechanisms are conserved in a broad range of cancer cell types, and are relevant to tumour progression and metastasis. We are now using the secondary cell system to work out how exosomes are packaged, how their secretion is regulated and how they then affect target cells, all fundamental questions that have been very difficult to address in vivo in other systems.

 

INTERPLAY BETWEEN CELL-CELL SIGNALLING, MEMBRANE TRAFFICKING AND SECRETION

One fundamental conclusion we have made from our previous studies and recent work in secondary cells is that not only do several signalling pathways play fundamental roles in controlling the trafficking of membranes within the cell, but trafficking also controls key intracellular signalling hubs like mTORC1 and regulates the type of secreted signals released to reprogramme other cells. Our ability to visualise the substructure of intracellular compartments in living secondary cells using confocal microscopy and more recently super-resolution 3D-SIM has shed new light on the biology that underpins this, in a field that has previously remained inaccessible to detailed cell biological analysis. For example, we have recently demonstrated that the BMP ligand Dpp is packaged into dense-core granules in secondary cells and its mating-dependent secretion drives new dense-core granule formation to replenish the pool of secretory compartments. Using different endogenous and fluorescent markers, we have also found that single cells make different types of exosome in different intracellular compartments. There is evidence that both of these mechanisms are evolutionarily conserved, and given the importance of exosomes and dense-core granules in disorders such as cancer and diabetes, as well as cellular processes like neurotransmission, these data have significant implications for our understanding of basic cell biology in health and disease.

 

HOW DO AMINO ACID TRANSPORTERS AND CELLULAR NUTRIENT SENSORS INTERACT WITH INSULIN AND mTORC1 SIGNALLING CASCADES?

Insulin and insulin-like growth factors have fundamental roles in nutrient-regulated metabolism and growth. Indeed, defective signalling by these molecules is known to be a critical factor in both diabetes and many forms of human cancer. More recently the rate of ageing and degenerative events in diseases such as Alzheimer’s and Parkinson’s Disease have also been associated with levels of insulin signalling and the activity of its downstream signalling target, the TORC1 kinase complex.

The powerful genetic approaches in the fruit fly Drosophila melanogaster have been instrumental in allowing our group and others over the last fifteen years to make major contributions to our understanding of insulin signalling and its link to a downstream nutrient-sensing signalling complex called mTORC1. These Drosophila-driven discoveries have led to the use of mTORC1 inhibitors in the clinic for some solid tumours, such as renal cancers. Our group has made a number of breakthroughs in the genetic dissection of the insulin signalling cascade and growth regulation over the years, typically initiating our studies with in vivo genetic approaches and then using state-of-the-art cell biological and physiological techniques to more closely analyse function. For example, we identified and characterised the fly homologue of the major tumour suppressor PTEN.

A collaboration between Deborah Goberdhan, Richard Boyd, David Meredith (who was previously in this department) and our group identified a specific class of amino acid transporters – the proton-assisted amino acid transporters (or PATs) – as unique regulators of mTORC1, growth, insulin signalling and insulin resistance in flies. Later work confirmed that mammalian PATs can also have the same effects and suggests that these molecules act as amino acid sensors that respond to amino acids in the luminal compartments of the late endosomes and lysosomes (LELs) and other compartments like the Golgi to activate mTOR at the membranes of these organelles. This work now dovetails with our studies of exosome biogenesis, which takes place in the same late endosomal compartments, and we are examining how these processes are co-ordinated. We are also studying the functions of several other amino acid transporters that appear to be involved in the mTORC1-regulated growth regulatory process. All of these transporters are good candidates as potential new drug targets in diseases such as cancer.

Our ability to visualise and genetically modulate the large late endosomal and lysosomal compartments in secondary cells has allowed us to investigate the roles of these and other compartments in mTORC1 signalling. Furthermore, since some genetic manipulations alter the maturation of these compartments, we are starting to use the secondary cell as a model for lysosomal disorders and to gauge the effects of changes in endolysosomal flux on subcellular processes associated with neurodegenerative disorders. This work is again highly complementary to our studies of exosome biology.

Our team

  • Clive Wilson
    Clive Wilson

    Professor of Cell and Developmental Genetics

  • Carina Gandy

    Researcher

  • Benjamin Kroeger

    Postgraduate Student

  • Siamak Redhai

    Postgraduate Student

  • Mark Wainwright

    Postdoctoral Research Scientist

  • Josephine Hellberg
    Josephine Hellberg

    Postgraduate Student

  • Felix Castellanos Suarez

    Postgraduate Student

  • Shih-Jung Fan
    Shih-Jung Fan

    Postdoctoral Research Scientist

  • Irina Stefana
    Irina Stefana

    Postdoctoral Research Scientist

  • Mihindukulasuriya Perera
    Mihindukulasuriya Perera

    Postgraduate Student

Related research themes