Protein tyrosine phosphatase signalling mechanisms
Protein tyrosine phosphatases (PTPs) are critical regulators of cellular signalling, acting together with protein tyrosine kinases to control phosphorylation-dependent processes. By removing phosphate groups from tyrosine residues, PTPs tune signalling pathways that govern cell growth, differentiation, adhesion, migration, and immune responses. Additionally, PTPs have important non-catalytic and scaffolding functions. Dysregulation of PTP function is implicated in numerous diseases, including cancer, autoimmunity, and metabolic diseases. Our research focuses on understanding the biochemical principles that dictate PTP specificity and activity towards substrates, as well as their integration into signalling networks. By mapping these mechanisms, we aim to uncover new therapeutic strategies for targeting aberrant phosphatase function.
Redox regulation of PTPs and kinases
PTPs are uniquely sensitive to changes in the cellular redox environment due to the reactive cysteine residue in their catalytic site. This cysteine can be reversibly oxidized, providing a mechanism for dynamic regulation of phosphatase activity in response to oxidative signals. Our interests expand to redox sensing by non-catalytic PTP cysteines as well as pseudophosphatases. Understanding these reversible redox switches offers insight into how cells translate oxidative cues into signalling outcomes.
While PTPs are well-known redox sensors, emerging evidence shows that protein tyrosine kinases (PTKs) are also subject to oxidative control. For example, we have demonstrated that the widely used PTP inhibitor pervanadate can oxidise and activate Src family kinases. This interplay between oxidant-sensitive phosphatases and kinases ensures that signalling pathways respond appropriately to metabolic and environmental cues. Our research investigates how these redox mechanisms maintain signalling fidelity and how their dysregulation contributes to pathological states such as cancer, T cell exhaustion and unhealthy ageing. By dissecting these processes, we aim to identify novel therapeutic targets that exploit redox vulnerabilities in signalling networks.
Redox dynamics and cell fate
The interplay between reactive oxygen species (ROS; such as hydrogen peroxide) production, antioxidant systems, and redox-sensitive proteins like PTPs shapes pathways controlling cell fate. Our research investigates how spatial and temporal patterns of redox changes coordinate these decisions, particularly in contexts such as development, immune activation, and cancer progression. By integrating biochemistry, cellular imaging and proteomic approaches, we aim to understand redox signalling dynamics and how they are impacted by the process of ageing.
Dynamic regulation of protein tyrosine phosphorylation (pTyr) by kinases and phosphatases enables cells to sense and respond to environmental changes. The widely used chemical pervanadate induces the accumulation of pTyr in mammalian cell lines. This effect is primarily attributed to its inhibition of protein tyrosine phosphatases (PTPs), leading to the assertion that PTPs are master gatekeepers of intracellular pTyr homeostasis. Here, we used several approaches to reveal that pervanadate disrupted cellular redox homeostasis and directly activated tyrosine kinases of the SRC family through the oxidation of specific cysteine residues. Mass spectrometry and biophysical approaches showed that pervanadate-induced oxidation of cysteine-188 and cysteine-280 activated SRC by disrupting autoinhibitory intramolecular interactions between the catalytic domain and the SH2/SH3 domains and by impairing SH2 domain binding to phosphopeptides, including the regulatory carboxyl-terminal tail phosphotyrosine-530. Redox-sensitive cysteine residues were essential for SRC to promote the overgrowth of mouse fibroblasts. Our findings call for a reevaluation of pervanadate-based experiments and demonstrate that SRC cysteines control its oncogenic properties.
Autotaxin (ATX), encoded by ENPP2, is a clinical target in pancreatic ductal adenocarcinoma (PDAC). ATX catalyzes the production of lysophosphatidic acid (LPA), an important regulator within the tumor microenvironment (TME), yet the pro-tumorigenic action of the ATX/LPA axis in PDAC remains unclear. Here, by interrogating patient samples and cell line datasets, we show that the PDAC TME, rather than cancer cells, is responsible for the majority of ENPP2 expression, and highlight a key role for cancer associated fibroblast (CAF)-derived ATX in autocrine and paracrine pro-tumorigenic signaling. Using the clinical-stage ATX inhibitor, IOA-289, we identified connective tissue growth factor (CTGF) as a downstream mediator of ATX signaling in the PDAC CAF-derived cell line, 0082T. Genetic ablation or pharmacological inhibition of ATX in 0082T CAFs reduced CTGF secretion via modulation of LPA/LPA receptor (LPAR) signaling. Despite the loss of ATX function, extracellular levels of LPA were paradoxically increased, indicating a role for ATX beyond its enzymatic activity and suggesting a role for its LPA chaperone function in the LPA/LPAR signaling in CAFs. As CAFs are the main source for CTGF in the PDAC TME, these findings suggest a role for ATX in promoting pro-tumorigenic microenvironment via modulation of CAF secretion, not only via its LPA-producing activity but also via its LPA chaperone function, providing a potential mechanism for the anti-tumor effects of ATX inhibition.
PTPRK is a receptor tyrosine phosphatase that is linked to the regulation of growth factor signalling and tumour suppression. It is stabilized at the plasma membrane by trans homophilic interactions upon cell-cell contact. PTPRK regulates cell-cell adhesion but is also reported to regulate numerous cancer-associated signalling pathways. However, the signalling mechanism of PTPRK remains to be determined. Here, we find that PTPRK regulates cell adhesion signalling, suppresses invasion and promotes collective, directed migration in colorectal cancer cells. In vivo, PTPRK supports recovery from inflammation-induced colitis. In addition, we confirm that PTPRK functions as a tumour suppressor in the mouse colon and in colorectal cancer xenografts. PTPRK regulates growth factor and adhesion signalling, and suppresses epithelial to mesenchymal transition (EMT). Contrary to the prevailing notion that PTPRK directly dephosphorylates EGFR, we find that PTPRK regulation of both EGFR and EMT is independent of its catalytic function. This suggests that additional adaptor and scaffold functions are important features of PTPRK signalling.