The broad, long-term objectives of the project are to characterize the structure, regulation and function of the protein tyrosine phosphatase (PTP) family of enzymes. It is now apparent that the coordinated and competing actions of both protein tyrosine kinases (PTKs) and PTPs are integrated in vivo to control such fundamental processes as growth and proliferation, differentiation, survival, motility and metabolism. Furthermore, disruption of the delicate balance between the action of PTPs and PTKs has been implicated in the etiology of human diseases, including cancer, diabetes and inflammation. Therefore, characterization of the PTPs is a prerequisite to gaining a complete understanding of the physiological consequences of tyrosine phosphorylation and how such signaling events are abrogated in disease. The focus of this proposal is the regulation of PTP function by reversible oxidation and inactivation, as a new tier of control of tyrosine phosphorylation-dependent signaling. In the previous funding period, a novel assay was developed, and extensively validated, that measures the reversible oxidation in cells of all the major categories of the PTP family. In this competitive renewal various tools that have been developed in the lab will be applied to examine the role of PTP oxidation in cancer models. In addition, the mechanisms underlying the reduction step in the process of reversible oxidation, which regenerates the active form of the PTP, but which has been neglected to date, will be characterized. It is anticipated that these studies will generate new insights into the regulation of tyrosine phosphorylation-dependent signal transduction, as well as new insights into the function of individual PTPs in cancer. To achieve this, the Specific Aims of the research program are: 1: To investigate the regulation and function of the receptor phosphatase PTP1 in cell and animal models of breast cancer, 2: To investigate the role of PTP oxidation in onset and bypass of oncogene-induced senescence, 3: To investigate mechanisms regulating the reduction and reactivation of oxidized PTP1B, and 4: To investigate the role of thioredoxin in reversible PTP oxidation.
Each cell is surrounded by a plasma membrane that represents a barrier to the outside world. However, the cell must be able to respond to changes in its external environment. This laboratory studies a process termed signal transduction, which is the mechanism by which cells register environmental stimuli and respond by changing their growth, differentiation, survival, movement or metabolism. The reversible addition and removal of phosphate to proteins, which is termed protein phosphorylation, is a crucial aspect of the mechanism of signal transduction. The activities of the enzymes that mediate the addition (kinases) and removal (phosphatases) of phosphate groups are coordinated in signal transduction pathways to mediate the cellular response to environmental stimuli and the function of these enzymes is frequently disrupted in human diseases, including cancer. This laboratory focuses on the family of signal transducing protein phosphatases known as Protein Tyrosine Phosphatases (PTPs) and their role in human disease. The characterization of the PTPs is a prerequisite to gaining a complete understanding of the physiological consequences of tyrosine phosphorylation and how such signaling events are abrogated in disease. The ability to modulate signal transduction pathways selectively holds enormous therapeutic potential. The first drugs directed against protein tyrosine kinases (PTKs) have now entered the market and represent breakthroughs in cancer therapy. However, the success rate is limited and these approaches remain in their infancy. The development of novel strategies to interrogate such protein phosphorylation-dependent signaling pathways will have a profound impact on drug development in cancer. In this context, the PTPs remain a largely untapped resource that can be exploited to reveal new insights into the regulation of signal transduction. It is now known that a wide variety of stimuli, including growth factors, hormones and cytokines, trigger the controlled production of reacive oxygen species (ROS), particularly hydrogen peroxide. This results in the reversible oxidation and inactivation of those PTPs that provide inhibitory constraint upon the signaling pathway. This mode of regulation, which is the focus of this proposal, applies broadly across the PTP family as a whole and as such reflects a new tier of control over tyrosine phosphorylation-dependent signaling under normal and pathophysiological conditions. We have developed novel assays to measure PTP oxidation in cells, which, together with various tools we have developed for analysis of PTP function, will be integrated with state of the art cell and animal models, to define critical tyrosine phosphorylation-dependent signaling events in cancer. By doing so we will open up unique perspectives on tyrosine phosphorylation-dependent signal transduction that will allow us to identify novel therapeutic targets and biomarkers from among the PTPs themselves or from within those signaling pathways that they regulate. Furthermore, although there is excitement in the field regarding the potential of the PTPs themselves as therapeutic targets, it is also clear that, due to the chemical properties of the PTP active site, they are challenging targets for drug development. The characterization of the regulatory role of reversible PTP oxidation may also suggest new therapeutic strategies for inhibition of the PTPs.
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