LFA-1 cluster formation in T-cells depends on L-plastin phosphorylation regulated by P90RSK and PP2A

RSK1 and RSK2 as therapeutic targets: an up-to-date snapshot of emerging data

INTRODUCTION

The four members of the p90 ribosomal S6 kinase (RSK) family are serine/threonine protein kinases, which are phosphorylated and activated by ERK1/2. RSK1/2/3 are further phosphorylated by PDK1. Receiving inputs from two major signaling pathways places RSK as a key signaling node in numerous pathologies. A plethora of RSK1/2 substrates have been identified, and in the majority of cases the causative roles these RSK substrates play in the pathology are unknown.

AREAS COVERED

The majority of studies have focused on RSK1/2 and their functions in a diverse group of cancers. However, RSK1/2 are known to have important functions in cardiovascular disease and neurobiological disorders. Based on the literature, we identified substrates that are common in these pathologies with the goal of identifying fundamental physiological responses to RSK1/2.

EXPERT OPINION

The core group of targets in pathologies driven by RSK1/2 are associated with the immune response. However, there is a paucity of the literature addressing RSK function in inflammation, which is critical to know as the pan RSK inhibitor, PMD-026, is entering phase II clinical trials for metastatic breast cancer. A RSK inhibitor has the potential to be used in numerous diverse diseases and disorders.

Predicting immunotherapy-related adverse events in late-stage non-small cell lung cancer with KARS G12C mutation treated with PD-1 inhibitors through combined assessment of LCP1 and ADPGK expression levels

OBJECTIVE

To evaluate the potential of leukocyte-specific protein 1 (LCP1) and adenosine diphosphate-dependent glucokinase (ADPGK) as predictive biomarkers for immunotherapy-related adverse events in late-stage non-small cell lung cancer (NSCLC) patients with the KARS G12C mutation undergoing treatment with programmed cell death protein-1 (PD-1) monoclonal antibodies.

METHODS

A total of 160 late-stage NSCLC patients with the KARS G12C mutation receiving PD-1 monoclonal antibody treatment were retrospectively analyzed. LCP1 and ADPGK expression levels were assessed at both mRNA and protein levels using validated methods. Statistical analyses, including correlation analysis, logistic regression, and receiver operating characteristic (ROC) curve analysis, were conducted to explore the association between LCP1 and ADPGK expression levels and the occurrence of immunotherapy-related adverse events.

RESULTS

The mRNA levels of LCP1 (2.43 ± 0.72 vs. 2.14 ± 0.67, t=2.311, P=0.023) and ADPGK (2.31 ± 0.61 vs. 1.98 ± 0.59, t=3.145, P=0.002) were significantly elevated in patients with adverse reactions. Similarly, protein levels of LCP1 (1.22 ± 0.28 vs. 1.07 ± 0.25, t=3.179, P=0.002) and ADPGK (1.01 ± 0.18 vs. 0.93 ± 0.19, t=2.488, P=0.015) were higher in this group. Correlation and logistic regression analyses revealed positive correlations between LCP1 and ADPGK mRNA levels and adverse event occurrence (LCP1: rho=0.186, P=0.019, OR=1.842; ADPGK: rho=0.246, P=0.002, OR=2.549). Protein levels of LCP1 and ADPGK also correlated with immunotherapy-related adverse events (LCP1: rho=0.254, P=0.001, OR=9.554; ADPGK: rho=0.19, P=0.016, OR=10.058). The combined assessment of LCP1 and ADPGK expression showed strong predictive power for identifying patients at increased risk of adverse events during PD-1 treatment (AUC=0.808), with the validation group achieving an AUC of 0.751.

CONCLUSION

LCP1 and ADPGK are potential independent predictive biomarkers for immunotherapy-related adverse events in late-stage NSCLC patients with the KARS G12C mutation. Their combined assessment may offer a valuable tool for risk stratification during PD-1 monoclonal antibody treatment.

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.

RSK inhibitors as potential anticancer agents: Discovery, optimization, and challenges

Ribosomal S6 kinase (RSK) family is a group of serine/threonine kinases, including four isoforms (RSK1/2/3/4). As a downstream effector of the Ras-mitogen-activated protein kinase (Ras-MAPK) pathway, RSK participates in many physiological activities such as cell growth, proliferation, and migration, and is intimately involved in tumor occurrence and development. As a result, it is recognized as a potential target for anti-cancer and anti-resistance therapies. There have been several RSK inhibitors discovered or designed in recent decades, but only two have entered clinical trials. Low specificity, low selectivity, and poor pharmacokinetic properties in vivo limit their clinical translation. Published studies performed structure optimization by increasing interaction with RSK, avoiding hydrolysis of pharmacophores, eliminating chirality, adapting to binding site shape, and becoming prodrugs. Besides enhancing efficacy, the focus of further design will move towards selectivity since there are functional differences among RSK isoforms. This review summarized the types of cancers associated with RSK, along with the structural characteristics and optimization process of the reported RSK inhibitors. Furthermore, we addressed the importance of RSK inhibitors' selectivity and discussed future drug development directions. This review is expected to shed light on the emergence of RSK inhibitors with high potency, specificity, and selectivity.

Efficient T Cell Migration and Activation Require L-Plastin

Rapid re-organization of the actin cytoskeleton supports T-cell trafficking towards immune sites and interaction with antigen presenting cells (APCs). F-actin rearrangement enables T-cell trafficking by stabilizing adhesion to vascular endothelial cells and promoting transendothelial migration. T-cell/APC immune synapse (IS) maturation also relies upon f-actin-anchored LFA-1:ICAM-1 ligation. Therefore, efficient T-cell responses require tight regulation of f-actin dynamics. In this review, we summarize how the actin-bundling protein L-plastin (LPL) regulates T-cell activation and migration. LPL enhances f-actin polymerization and also directly binds to the β2 chain of the integrin LFA-1 to support intercellular adhesion and IS formation in human and murine T cells. LPL- deficient T cells migrate slowly in response to chemo-attractants such as CXCL12, CCL19, and poorly polarize towards ICAM-1. Loss of LPL impairs thymic egress and intranodal motility. LPL is also required for T-cell IS maturation with APCs, and therefore for efficient cytokine production and proliferation. LPL^-/- mice are less susceptible to T-cell mediated pathologies, such as allograft rejection and experimental autoimmune encephalomyelitis (EAE). LPL activity is regulated by its N-terminal “headpiece”, which contains serine and threonine phosphorylation and calcium- and calmodulin-binding sites. LPL phosphorylation is required for lamellipodia formation during adhesion and migration, and also for LFA-1 clustering during IS formation. However, the precise molecular interactions by which LPL supports T-cell functional responses remain unclear. Future studies elucidating LPL-mediated regulation of T-cell migration and/or activation may illuminate pathways for therapeutic targeting in T-cell-mediated diseases.

Allosteric regulation controls actin-bundling properties of human plastins

Plastins/fimbrins are conserved actin-bundling proteins contributing to motility, cytokinesis and other cellular processes by organizing strikingly different actin assemblies as in aligned bundles and branched networks. We propose that this ability of human plastins stems from an allosteric communication between their actin-binding domains (ABD1/2) engaged in a tight spatial association. Here we show that ABD2 can bind actin three orders of magnitude stronger than ABD1, unless the domains are involved in an equally strong inhibitory engagement. A mutation mimicking physiologically relevant phosphorylation at the ABD1-ABD2 interface greatly weakened their association, dramatically potentiating actin cross-linking. Cryo-EM reconstruction revealed the ABD1-actin interface and enabled modeling of the plastin bridge and domain separation in parallel bundles. We predict that a strong and tunable allosteric inhibition between the domains allows plastins to modulate the cross-linking strength, contributing to remodeling of actin assemblies of different morphologies defining the unique place of plastins in actin organization.