Roles of PI 3-kinase isoforms in autophagy and endosomal membrane dynamics
Lead Research Organisation:
Queen Mary University of London
Department Name: Barts Cancer Institute
Abstract
One of the most fundamental component parts of the human body is a structure termed a cell. Every cell is surrounded by a membrane of fat which maintains its identity separate from the surrounding environment. Furthermore, every cell is subdivided into more compartments by itself containing discrete and unique membrane-bound structures termed organelles. In order for a cell to function it must be able to perform a number of roles including communication with the extracellular milieu, the regulated transfer of material between organelles and the recycling of aged material within the cell itself. Defects in any of these functions can lead to abberations which ultimately cause the cell to malfunction and lead to cancer, the unregulated growth of cells.
Our laboratory works on catalysts within the cell termed PI3Ks. PI3Ks are able to specifically manipulate the composition of the cellular membranes. These manipulations are critical to ensure fidelity of the transfer of material between organelles and between the external environment and organelles.
The importance of these PI3Ks in maintaining normal cellular functions is highlighted by the fact that they are compromised in a high percentage of tumors. Consequently it is obvious that if we wish to tackle the causes of cancer and try to cure patients suffering from cancer it is vital that we know how PI3Ks function in whole organisms. The main problem with this avenue of enquiry however is that there are numerous flavors of PI3K within cells and each performs a distinct role within the cell. To this end our laboratory generate mice models where the activity of discrete PI3Ks are specifically ablated, both at the level of cells and the whole organism. By this methodology we are able to assign specific roles to each PI3K and in combination with drug companies design small molecule inhibitors targeted towards each PI3K. These small molecule inhibitors are then tested in directed experiments to see whether they will be of any therapeutic use in tackling cancer and other health issues arising from defective PI3K signalling.
Our laboratory works on catalysts within the cell termed PI3Ks. PI3Ks are able to specifically manipulate the composition of the cellular membranes. These manipulations are critical to ensure fidelity of the transfer of material between organelles and between the external environment and organelles.
The importance of these PI3Ks in maintaining normal cellular functions is highlighted by the fact that they are compromised in a high percentage of tumors. Consequently it is obvious that if we wish to tackle the causes of cancer and try to cure patients suffering from cancer it is vital that we know how PI3Ks function in whole organisms. The main problem with this avenue of enquiry however is that there are numerous flavors of PI3K within cells and each performs a distinct role within the cell. To this end our laboratory generate mice models where the activity of discrete PI3Ks are specifically ablated, both at the level of cells and the whole organism. By this methodology we are able to assign specific roles to each PI3K and in combination with drug companies design small molecule inhibitors targeted towards each PI3K. These small molecule inhibitors are then tested in directed experiments to see whether they will be of any therapeutic use in tackling cancer and other health issues arising from defective PI3K signalling.
Technical Summary
PI 3-kinases (PI3Ks) are signalling enzymes that play key roles in cell physiology. Deregulated PI3K signalling has been implicated in cancer, inflammation and diabetes, and PI3Ks are being pursued as new therapeutic targets by the pharmaceutical industry. Mammals have 8 distinct isoforms of PI3K, several of which (p110a, p110b and vps34p) have been implicated in the regulation of membrane dynamics with respect to autophagy and endosomal dynamics.The current proposal aims to investigate how both autophagy and endosomal dynamics are regulated by members of the PI3K family.
Autophagy (Self Eating) is a cellular phenomenon whereby cytosolic components are sequestered within a double membrane structure and irreversibly degradated inside lysosomes. Autophagy has recently been linked to a wide range of human pathologies, including cancer, neurodegeneration and vacuolar myopathies but the mechanistic details of how autophagy is regulated remain largely obscure. It is believed that one of the class I PI3Ks directs an inhibitory signal to autophagic processes, the isoform is currently unknown but we have preliminary evidence that it is p110a. Conversely vps34p, a class III PI3K, sends a stimulatory signal to boost levels of autophagy within the cell. The nature of these signals may reflect a lipid kinase event in the production of PI3P, however it is possible that vps34p plays a scaffolding role in maintaining the stoichiometry of a protein complex vital in the regulation of autophagy.
Proper control of the flux of membranes through endosomes is important as misregulation can lead to prooncogenic signaling from internalized receptors that are destined for the lysosomes in order to ablate their progrowth signals. A failure in lysosomal delivery will prolong the oncogenic signaling and thus predispose the cell to becoming cancerous. Membrane trafficking within endosomes is in part controlled by the localized production of PI3P. The source of the PI3P is a disputed area and be made by vps34p or by the sequential action of class I PI3Ks and 5- and 4-phosphatases.
This proposal will make use of newly created PI3K gene-targeted mice and cell-based models to resolve fundamental issues concerning the roles of PI3K isoforms in autophagy and endosomal membrane trafficking and endocytosis. Increased understanding of these phenonomena is not only important from a fundamental science point of view but may also enable modulation of these cellular phenomena in a therapeutic manner through the application of small molecule inhibitors directed against distinct PI3K isoforms.
Autophagy (Self Eating) is a cellular phenomenon whereby cytosolic components are sequestered within a double membrane structure and irreversibly degradated inside lysosomes. Autophagy has recently been linked to a wide range of human pathologies, including cancer, neurodegeneration and vacuolar myopathies but the mechanistic details of how autophagy is regulated remain largely obscure. It is believed that one of the class I PI3Ks directs an inhibitory signal to autophagic processes, the isoform is currently unknown but we have preliminary evidence that it is p110a. Conversely vps34p, a class III PI3K, sends a stimulatory signal to boost levels of autophagy within the cell. The nature of these signals may reflect a lipid kinase event in the production of PI3P, however it is possible that vps34p plays a scaffolding role in maintaining the stoichiometry of a protein complex vital in the regulation of autophagy.
Proper control of the flux of membranes through endosomes is important as misregulation can lead to prooncogenic signaling from internalized receptors that are destined for the lysosomes in order to ablate their progrowth signals. A failure in lysosomal delivery will prolong the oncogenic signaling and thus predispose the cell to becoming cancerous. Membrane trafficking within endosomes is in part controlled by the localized production of PI3P. The source of the PI3P is a disputed area and be made by vps34p or by the sequential action of class I PI3Ks and 5- and 4-phosphatases.
This proposal will make use of newly created PI3K gene-targeted mice and cell-based models to resolve fundamental issues concerning the roles of PI3K isoforms in autophagy and endosomal membrane trafficking and endocytosis. Increased understanding of these phenonomena is not only important from a fundamental science point of view but may also enable modulation of these cellular phenomena in a therapeutic manner through the application of small molecule inhibitors directed against distinct PI3K isoforms.