A photoaffinity labeling strategy identified EF1A1 as a binding protein of cyclic dinucleotide 2'3'-cGAMP

The eEF1A protein in cancer: Clinical significance, oncogenic mechanisms, and targeted therapeutic strategies

Eukaryotic elongation factor 1A (eEF1A) is among the most abundant proteins in eukaryotic cells. Evolutionarily conserved across species, eEF1A is in charge of translation elongation for protein biosynthesis as well as a plethora of non-translational moonlighting functions for cellular homeostasis. In malignant cells, however, eEF1A becomes a pleiotropic driver of cancer progression via a broad diversity of pathways, which are not limited to hyperactive translational output. In the past decades, mounting studies have demonstrated the causal link between eEF1A and carcinogenesis, gaining deeper insights into its multifaceted mechanisms and corroborating its value as a prognostic marker in various cancers. On the other hand, an increasing number of natural and synthetic compounds were discovered as anticancer eEF1A-targeting inhibitors. Among them, plitidepsin was approved for the treatment of multiple myeloma whereas metarrestin was currently under clinical development. Despite significant achievements in these two interrelated fields, hitherto there lacks a systematic examination of the eEF1A protein in the context of cancer research. Therefore, the present work aims to delineate its clinical implications, molecular oncogenic mechanisms, and targeted therapeutic strategies as reflected in the ever expanding body of literature, so as to deepen mechanistic understanding of eEF1A-involved tumorigenesis and inspire the development of eEF1A-targeted chemotherapeutics and biologics.

Tumor Exosomal ENPP1 Hydrolyzes cGAMP to Inhibit cGAS-STING Signaling

To evade immune surveillance, tumor cells express ectonucleotide pyrophosphatase phosphodiesterase 1 (ENPP1) on the surface of their membrane, which degrades extracellular cyclic GMP-AMP (cGAMP), thereby inhibiting the cyclic GMP-AMP synthase (cGAS) stimulator of interferon gene (STING) DNA-sensing pathway. To fully understand this tumor stealth mechanism, it is essential to determine whether other forms of ENPP1 with hydrolytic cGAMP activity also are present in the tumor microenvironment to regulate this innate immune pathway. Herein, it is reported that various tumor-derived exosomes carry ENPP1, and can hydrolyze synthetic 2'3'-cGAMP and endogenous 2'3'-cGAMP produced by cells to inhibit cGAS-STING pathway in immune cells. Moreover, tumor exosomal ENPP1 also can hydrolyze 2'3'-cGAMP bound to LL-37 (an effective transporter of 2'3'-cGAMP) to inhibit STING signaling. Furthermore, high expression of ENPP1 in exosomes is observed isolated from human breast and lung cancer tissue, and tumor exosomal ENPP1 inhibited the immune infiltration of CD8+ T cells and CD4+ T cells. The results elucidate the essential function of tumor exosomal ENPP1 in the cGAS-STING pathway, furthering understanding of the crosstalk between the tumor cells and immune system.

Chemoproteomics, A Broad Avenue to Target Deconvolution

As a vital project of forward chemical genetic research, target deconvolution aims to identify the molecular targets of an active hit compound. Chemoproteomics, either with chemical probe-facilitated target enrichment or probe-free, provides a straightforward and effective approach to profile the target landscape and unravel the mechanisms of action. Canonical methods rely on chemical probes to enable target engagement, enrichment, and identification, whereas click chemistry and photoaffinity labeling techniques improve the efficiency, sensitivity, and spatial accuracy of target recognition. In comparison, recently developed probe-free methods detect protein-ligand interactions without the need to modify the ligand molecule. This review provides a comprehensive overview of different approaches and recent advancements for target identification and highlights the significance of chemoproteomics in investigating biological processes and advancing drug discovery processes.

Selective STING stimulation in dendritic cells primes antitumor T cell responses

T cells that recognize tumor antigens are crucial for mounting antitumor immune responses. Induction of antitumor T cells in immunogenic tumors depends on STING, the intracellular innate immune receptor for cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) and related cyclic dinucleotides (CDNs). However, the optimal way to leverage STING activation in nonimmunogenic tumors is still unclear. Here, we show that cGAMP delivery by intratumoral injection of virus-like particles (cGAMP-VLP) led to differentiation of circulating tumor-specific T cells, decreased tumor regulatory T cells (T_regs), and antitumoral responses that synergized with PD1 blockade. By contrast, intratumoral injection of the synthetic CDN ADU-S100 led to tumor necrosis and systemic T cell activation but simultaneously depleted immune cells from injected tumors and induced minimal priming of circulating tumor-specific T cells. The antitumor effects of cGAMP-VLP required type 1 conventional dendritic cells (cDC1), whereas ADU-S100 eliminated cDC1 from injected tumors. cGAMP-VLP preferentially targeted STING in dendritic cells at a 1000-fold smaller dose than ADU-S100. Subcutaneous administration of cGAMP-VLP showed synergy when combined with PD1 blockade or a tumor T_reg-depleting antibody to elicit systemic tumor-specific T cells and antitumor activity, leading to complete and durable tumor eradication in the case of tumor T_reg depletion. These findings show that cell targeting of STING stimulation shapes the antitumor T cell response and identify a therapeutic strategy to enhance T cell-targeted immunotherapy.

Protocol for identification and validation of 2'3'-cGAMP-binding proteins by photoaffinity probes

Mammalian cyclic dinucleotide 2′3′-cGAMP functions as a second messenger in innate immune response. Here, we report a protocol to utilize 2′3′-cGAMP photoaffinity probes to capture 2′3′-cGAMP-binding or 2′3′-cGAMP-interacting proteins from HeLa cell lysate for in-gel visualization by fluorescent imaging or identification by SILAC–based quantitative MS. Further validation is also executed using photoaffinity probes to demonstrate the direct interaction of 2′3′-cGAMP with purified target proteins in vitro or endogenous target proteins in 293T cells.

For complete details on the use and execution of this profile, please refer to Hou et al. (2021).

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Strategy for identification of 2′3′-cGAMP interactome by photoaffinity probes

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Purification of EF1A1 in EF1 complex and validation of its binding with 2′3′-cGAMP

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Validate 2′3′-cGAMP interactors in vitro and in 293T cells using photoaffinity probes