Regulatory Functions of Protein Tyrosine Phosphatase Receptor Type O in Immune Cells

Analysis of Receptor-Type Protein Tyrosine Phosphatase Extracellular Regions with Insights from AlphaFold

The receptor-type protein tyrosine phosphatases (RPTPs) are involved in a wide variety of physiological functions which are mediated via their diverse extracellular regions. They play key roles in cell-cell contacts, bind various ligands and are regulated by dimerization and other processes. Depending on the subgroup, they have been described as everything from 'rigid rods' to 'floppy tentacles'. Here, we review current experimental structural knowledge on the extracellular region of RPTPs and draw on AlphaFold structural predictions to provide further insights into structure and function of these cellular signalling molecules, which are often mutated in disease and are recognised as drug targets. In agreement with experimental data, AlphaFold predicted structures for extracellular regions of R1, and R2B subgroup RPTPs have an extended conformation, whereas R2B RPTPs are twisted, reflecting their high flexibility. For the R3 PTPs, AlphaFold predicts that members of this subgroup adopt an extended conformation while others are twisted, and that certain members, such as CD148, have one or more large, disordered loop regions in place of fibronectin type 3 domains suggested by sequence analysis.

An in-line method for high-throughput screening of protein tyrosine phosphatase receptor type O inhibitors by capillary electrophoresis based on electrophoretically mediated microanalysis

Protein tyrosine phosphatase receptor type O (PTPRO) plays an important role in inflammation-related pathways and has become an emerging drug target. In this study, we developed an in-line capillary electrophoresis (CE) method for the investigation of the enzymatic activity of PTPRO, which was based on electrophoretically mediated microanalysis (EMMA). After a thorough method validation of the optimized conditions, this protocol was successfully employed to determine the kinetics of PTPRO as well as the half-maximal inhibitory concentration (IC50) of two typical PTPRO inhibitors. The final results were consistent with the values obtained through classical ultraviolet-visible (UV-vis) spectrophotometry. Our new method exhibited improved accuracy and reduced consumption, avoiding the disadvantages of traditional methods. This work provides a new strategy for PTPRO enzyme kinetic studies as well as inhibitory activity determination through capillary electrophoresis for the first time.

Age-related decline in hippocampal tyrosine phosphatase PTPRO is a mechanistic factor in chemotherapy-related cognitive impairment

Chemotherapy-related cognitive impairment (CRCI) or "chemo brain" is a devastating neurotoxic sequela of cancer-related treatments, especially for the elderly individuals. Here we show that PTPRO, a tyrosine phosphatase, is highly enriched in the hippocampus, and its level is tightly associated with neurocognitive function but declined significantly during aging. To understand the protective role of PTPRO in CRCI, a mouse model was generated by treating Ptpro-/- female mice with doxorubicin (DOX) because Ptpro-/- female mice are more vulnerable to DOX, showing cognitive impairments and neurodegeneration. By analyzing PTPRO substrates that are neurocognition-associated tyrosine kinases, we found that SRC and EPHA4 are highly phosphorylated/activated in the hippocampi of Ptpro-/- female mice, with increased sensitivity to DOX-induced CRCI. On the other hand, restoration of PTPRO in the hippocampal CA3 region significantly ameliorate CRCI in Ptpro-/- female mice. In addition, we found that the plant alkaloid berberine (BBR) is capable of ameliorating CRCI in aged female mice by upregulating hippocampal PTPRO. Mechanistically, BBR upregulates PTPRO by downregulating miR-25-3p, which directly targeted PTPRO. These findings collectively demonstrate the protective role of hippocampal PTPRO against CRCI.

PTPRO-related CD8+ T-cell signatures predict prognosis and immunotherapy response in patients with breast cancer

BACKGROUND

Poor immunogenicity and extensive immunosuppressive T-cell infiltration in the tumor immune microenvironment (TIME) have been identified as potential barriers to immunotherapy success in "immune-cold" breast cancers. Thus, it is crucial to identify biomarkers that can predict immunotherapy efficacy. Protein tyrosine phosphatase receptor type O (PTPRO) regulates multiple kinases and pathways and has been implied to play a regulatory role in immune cell infiltration in various cancers.

METHODS

ESTIMATE and single-sample gene set enrichment analysis (ssGSEA) were performed to uncover the TIME landscape. The correlation analysis of PTPRO and immune infiltration was performed to characterize the immune features of PTPRO. Univariate and multivariate Cox analyses were applied to determine the prognostic value of various variables and construct the PTPRO-related CD8⁺ T-cell signatures (PTSs). The Kaplan-Meier curve and the receiver operating characteristic (ROC) curve were used to estimate the performance of PTS in assessing prognosis and immunotherapy response in multiple validation datasets.

RESULTS

High PTPRO expression was related to high infiltration levels of CD8⁺ T cells, as well as macrophages, activated dendritic cells (aDCs), tumor-infiltrating lymphocytes (TILs), and Th1 cells. Given the critical role of CD8⁺ T cells in the TIME, we focused on the impact of PTPRO expression on CD8⁺ T-cell infiltration. The prognostic PTS was then constructed using the TCGA training dataset. Further analysis showed that the PTS exhibited favorable prognostic performance in multiple validation datasets. Of note, the PTS could accurately predict the response to immune checkpoint inhibitors (ICIs).

CONCLUSION

PTPRO significantly impacts CD8⁺ T-cell infiltration in breast cancer, suggesting a potential role of immunomodulation. PTPRO-based PTS provides a new immune cell paradigm for prognosis, which is valuable for immunotherapy decisions in cancer patients.