Ultrasensitivity in the Cofilin Signaling Module: A Mechanism for Tuning T Cell Responses

Human T-cell receptor triggering requires inactivation of Lim kinase-1 by Slingshot-1 phosphatase

Actin dynamics control early T-cell receptor (TCR) signalling during T-cell activation. However, the precise regulation of initial actin rearrangements is not completely understood. Here, we have investigated the regulatory role of the phosphatase Slingshot-1 (SSH1) in this process. Our data show that SSH1 rapidly polarises to nascent cognate synaptic contacts and later relocalises to peripheral F-actin networks organised at the mature immunological synapse. Knockdown of SSH1 expression by CRISPR/Cas9-mediated genome editing or small interfering RNA reveal a regulatory role for SSH1 in CD3ε conformational change, allowing Nck binding and proper downstream signalling and immunological synapse organisation. TCR triggering induces SSH1-mediated activation of actin dynamics through a mechanism mediated by Limk-1 inactivation. These data suggest that during early TCR activation, SSH1 is required for rapid F-actin rearrangements that mediate initial conformational changes of the TCR, integrin organisation and proximal signalling events for proper synapse organisation. Therefore, the SSH1 and Limk-1 axis is a key regulatory element for full T cell activation.

Targeting MMP9 in CTNNB1 mutant hepatocellular carcinoma restores CD8+ T cell-mediated antitumour immunity and improves anti-PD-1 efficacy

OBJECTIVE

The gain of function (GOF) CTNNB1 mutations (CTNNB1 GOF ) in hepatocellular carcinoma (HCC) cause significant immune escape and resistance to anti-PD-1. Here, we aimed to investigate the mechanism of CTNNB1 GOF HCC-mediated immune escape and raise a new therapeutic strategy to enhance anti-PD-1 efficacy in HCC.

DESIGN

RNA sequencing was performed to identify the key downstream genes of CTNNB1 GOF associated with immune escape. An in vitro coculture system, murine subcutaneous or orthotopic models, spontaneously tumourigenic models in conditional gene-knock-out mice and flow cytometry were used to explore the biological function of matrix metallopeptidase 9 (MMP9) in tumour progression and immune escape. Single-cell RNA sequencing and proteomics were used to gain insight into the underlying mechanisms of MMP9.

RESULTS

MMP9 was significantly upregulated in CTNNB1 GOF HCC. MMP9 suppressed infiltration and cytotoxicity of CD8+ T cells, which was critical for CTNNB1 GOF to drive the suppressive tumour immune microenvironment (TIME) and anti-PD-1 resistance. Mechanistically, CTNNB1 GOF downregulated sirtuin 2 (SIRT2), resulting in promotion of β-catenin/lysine demethylase 4D (KDM4D) complex formation that fostered the transcriptional activation of MMP9. The secretion of MMP9 from HCC mediated slingshot protein phosphatase 1 (SSH1) shedding from CD8+ T cells, leading to the inhibition of C-X-C motif chemokine receptor 3 (CXCR3)-mediated intracellular of G protein-coupled receptors signalling. Additionally, MMP9 blockade remodelled the TIME and potentiated the sensitivity of anti-PD-1 therapy in HCC.

CONCLUSIONS

CTNNB1 GOF induces a suppressive TIME by activating secretion of MMP9. Targeting MMP9 reshapes TIME and potentiates anti-PD-1 efficacy in CTNNB1 GOF HCC.

Receptor dynamics regulates actin polymerization state through phosphorylation of cofilin in mast cells

Aggregation of IgE bound to the high-affinity IgE receptor (FcεRI) by a multivalent antigen induces mast cell activation, while disaggregation of aggregated FcεRI by monomer hapten immediately terminates degranulation mediated by dephosphorylation of Syk and mediates a decrease in intracellular Ca²⁺ concentration ([Ca²⁺]_i). The actin polymerization state is intimately involved in mast cell activation mediated by FcεRI aggregation. However, the relation between aggregation-disaggregation of FcεRI and actin rearrangement in mast cells is not well understood. The addition of a multivalent antigen rapidly depolymerized actin filaments, while the subsequent addition of monomer hapten rapidly recovered actin polymerization. Whereas cofilin, an actin-severing protein, was temporally dephosphorylated several minutes after a multivalent antigen stimulation and the addition of monomer hapten rapidly increased cofilin phosphorylation level within 30 s. The removal of extracellular Ca²⁺ instead of monomer hapten addition did not restore cofilin phosphorylation, suggesting that the significant decrease in [Ca²⁺]_i by monovalent hapten was not a critical reason for the actin rearrangement. Additionally, monovalent hapten did not completely reduce [Ca²⁺]_i in mast cells pretreated with jasplakinolide, an inhibitor of actin depolymerization. These results suggest that the multivalent antigen-induced actin depolymerization mediated by cofilin dephosphorylation, and the subsequent addition of monovalent hapten in the F-actin severing state efficiently elicited actin re-polymerization by cofilin phosphorylation.

Slingshot homolog-1 expression is a poor prognostic factor of pT1 bladder urothelial carcinoma after transurethral resection

Objective

Slingshot homolog-1 (SSH-1) shows an important role in the occurrence and development in various tumors. While, the expression and prognostic implications of SSH-1 in bladder urothelial carcinoma (UC) remain unclear and thus were addressed in this study.

Methods

Immunohistochemistry (IHC) was performed on tissue microarrays composed of 624 bladder UC specimens after transurethral resection of bladder tumor (TUR-BT) to detect SSH-1 expression. The clinic-pathological features were compared between SSH-1( +) and SSH-1(−) subgroups. The Kaplan–Meier curve with log-rank test and univariate/multivariate Cox regression model with stepwise backward elimination methods were performed for survival analyses.

Results

In this study, 359 (57.53%) specimens were detected with SSH-1 expression. SSH-1 positivity was significantly associated with higher pathological grade (p = 0.020), lymphovascular invasion (p = 0.006), tumor recurrence (p < 0.001) and progression (p < 0.001) in bladder UC. Besides, SSH-1 positivity predicted a shorter overall survival (OS, p = 0.024), recurrence-free survival (RFS, p < 0.001), progression-free survival (PFS, p = 0.002) and cancer-specific survival (CSS, p = 0.047). Multivariate Cox proportional hazard analysis showed that tumor size (p = 0.007), lymphovascular invasion (p = 0.003), recurrence (p < 0.001), progression (p < 0.001) and SSH-1 expression (p = 0.015) were predictors of poor prognosis in bladder UC patients.

Conclusions

SSH-1 expression was associated with undesirable clinic-pathological characteristics and poor post-operative prognosis in bladder UC patients. SSH-1 might play an important role in bladder UC and serve as a promising predictor of oncological outcomes in patients with bladder UC.

Regulation of CD4+ T Cell Signaling and Immunological Synapse by Protein Tyrosine Phosphatases: Molecular Mechanisms in Autoimmunity

T cell activation and effector function is mediated by the formation of a long-lasting interaction established between T cells and antigen-presenting cells (APCs) called immunological synapse (IS). During T cell activation, different signaling molecules as well as the cytoskeleton and the endosomal compartment are polarized to the IS. This molecular dynamics is tightly regulated by phosphorylation networks, which are controlled by protein tyrosine phosphatases (PTPs). While some PTPs are known to be important regulators of adhesion, ligand discrimination or the stimulation threshold, there is still little information about the regulatory role of PTPs in cytoskeleton rearrangements and endosomal compartment dynamics. Besides, spatial and temporal regulation of PTPs and substrates at the IS is only barely known. Consistent with an important role of PTPs in T cell activation, multiple mutations as well as altered expression levels or dynamic behaviors have been associated with autoimmune diseases. However, the precise mechanism for the regulation of T cell activation and effector function by PTPs in health and autoimmunity is not fully understood. Herein, we review the current knowledge about the regulatory role of PTPs in CD4⁺ T cell activation, IS assembly and effector function. The potential molecular mechanisms mediating the action of these enzymes in autoimmune disorders are discussed.

Phosphatase of Regenerating Liver-1 (PRL-1) Regulates Actin Dynamics During Immunological Synapse Assembly and T Cell Effector Function

The regulatory role of most dual specific phosphatases during T cell activation remains unknown. Here, we have studied the expression and function of phosphatases of regenerating liver (PRLs: PRL-1, PRL-2, and PRL-3) during T cell activation, as well as, the dynamic delivery of PRL-1 to the Immunological Synapse (IS). We found that T cell activation downregulates the expression of PRL-2, resulting in an increased PRL-1/PRL-2 ratio. PRL-1 redistributed at the IS in two stages: Initially, it was transiently accumulated at scanning membranes enriched in CD3 and actin, and at later times, it was delivered at the contact site from pericentriolar, CD3ζ-containing, vesicles. Once at the established IS, PRL-1 distributed to LFA-1 and CD3ε sites. Remarkably, PRL-1 was found to regulate actin dynamics during IS assembly and the secretion of IL-2. Moreover, pharmacological inhibition of the catalytic activity of the three PRLs reduced the secretion of IL-2. These results provide evidence indicating a regulatory role of PRL-1 during IS assembly and highlight the involvement of PRLs in immune responses by mature T cells.

P21-activated kinase 2 is essential in maintenance of peripheral Foxp3+ regulatory T cells

The p21‐activated kinase 2 (Pak2), an effector molecule of the Rho family GTPases Rac and Cdc42, regulates diverse functions of T cells. Previously, we showed that Pak2 is required for development and maturation of T cells in the thymus, including thymus‐derived regulatory T (Treg) cells. However, whether Pak2 is required for the functions of various subsets of peripheral T cells, such as naive CD4 and helper T‐cell subsets including Foxp3⁺ Treg cells, is unknown. To determine the role of Pak2 in CD4 T cells in the periphery, we generated inducible Pak2 knockout (KO) mice, in which Pak2 was deleted in CD4 T cells acutely by administration of tamoxifen. Temporal deletion of Pak2 greatly reduced the number of Foxp3⁺ Treg cells, while minimally affecting the homeostasis of naive CD4 T cells. Pak2 was required for proliferation and Foxp3 expression of Foxp3⁺ Treg cells upon T‐cell receptor and interleukin‐2 stimulation, differentiation of in vitro induced Treg cells, and activation of naive CD4 T cells. Together, Pak2 is essential in maintaining the peripheral Treg cell pool by providing proliferation and maintenance signals to Foxp3⁺ Treg cells.

Gene Expression Profiles of Human Phosphotyrosine Phosphatases Consequent to Th1 Polarisation and Effector Function

Phosphotyrosine phosphatases (PTPs) constitute a complex family of enzymes that control the balance of intracellular phosphorylation levels to allow cell responses while avoiding the development of diseases. Despite the relevance of CD4 T cell polarisation and effector function in human autoimmune diseases, the expression profile of PTPs during T helper polarisation and restimulation at inflammatory sites has not been assessed. Here, a systematic analysis of the expression profile of PTPs has been carried out during Th1-polarising conditions and upon PKC activation and intracellular raise of Ca²⁺ in effector cells. Changes in gene expression levels suggest a previously nonnoted regulatory role of several PTPs in Th1 polarisation and effector function. A substantial change in the spatial compartmentalisation of ERK during T cell responses is proposed based on changes in the dose of cytoplasmic and nuclear MAPK phosphatases. Our study also suggests a regulatory role of autoimmune-related PTPs in controlling T helper polarisation in humans. We expect that those PTPs that regulate T helper polarisation will constitute potential targets for intervening CD4 T cell immune responses in order to generate new therapies for the treatment of autoimmune diseases.