Antioxidant functions of DHHC3 suppress anti-cancer drug activities

Post-translational modifications in drug resistance

Resistance to antitumor drugs, antimicrobial drugs, and antiviral drugs severely limits treatment effectiveness and cure rate of diseases. Protein post-translational modifications (PTMs) represented by glycosylation, ubiquitination, SUMOylation, acetylation, phosphorylation, palmitoylation, and lactylation are closely related to drug resistance. PTMs are typically achieved by adding sugar chains (glycosylation), small proteins (ubiquitination), lipids (palmitoylation), or functional groups (lactylation) to amino acid residues. These covalent additions are usually the results of signaling cascades and could be reversible, with the triggering mechanisms depending on the type of modifications. PTMs are involved in antitumor drug resistance, not only as inducers of drug resistance but also as targets for reversing drug resistance. Bacteria exhibit multiple PTMs-mediated antimicrobial drug resistance. PTMs allow viral proteins and host cell proteins to form complex interaction networks, inducing complex antiviral drug resistance. This review summarizes the important roles of PTMs in drug resistance, providing new ideas for exploring drug resistance mechanisms, developing new drug targets, and guiding treatment plans.

ZDHHC3-mediated SCAP S-acylation promotes cholesterol biosynthesis and tumor immune escape in hepatocellular carcinoma

Cholesterol metabolism reprogramming plays essential roles in hepatocellular carcinoma (HCC). However, precisely how cholesterol metabolism is dysregulated is not clear. Here, we show that the palmitoyltransferase ZDHHC3 and depalmitoylase ABHD17A regulate HCC cell cholesterol biosynthesis by dynamically S-acylating SREBP cleavage-activating protein (SCAP). SCAP S-acylation by ZDHHC3 at C264 antagonizes HACE1-mediated SCAP ubiquitination. Intriguingly, SREBP2 transcriptionally upregulates ZDHHC3 to form a positive feedback loop, which explains why negative feedback regulation of SCAP/SREBP2 signaling fails in HCC. Increased cholesterol in the tumor microenvironment (TME) restrains CD4+ T cell cytotoxicity. Hence, the cholesterol metabolism reprogramming and cholesterol level alternation in the TME cooperate to promote HCC development. We identified a small-molecule inhibitor of ZDHHC3 that, combined with anti-PD-1 immunotherapy, inhibited diethyl nitrosamine (DEN)/CCl4-induced HCC growth in mice. ZDHHC3-mediated SCAP S-acylation reprograms cholesterol metabolism and promotes HCC immune escape. ZDHHC3 is thus identified as a rational chemotherapy target for HCC.

Protein lipidation in cancer: mechanisms, dysregulation and emerging drug targets

Protein lipidation describes a diverse class of post-translational modifications (PTMs) that is regulated by over 40 enzymes, targeting more than 1,000 substrates at over 3,000 sites. Lipidated proteins include more than 150 oncoproteins, including mediators of cancer initiation, progression and immunity, receptor kinases, transcription factors, G protein-coupled receptors and extracellular signalling proteins. Lipidation regulates the physical interactions of its protein substrates with cell membranes, regulating protein signalling and trafficking, and has a key role in metabolism and immunity. Targeting protein lipidation, therefore, offers a unique approach to modulate otherwise undruggable oncoproteins; however, the full spectrum of opportunities to target the dysregulation of these PTMs in cancer remains to be explored. This is attributable in part to the technological challenges of identifying the targets and the roles of protein lipidation. The early stage of drug discovery for many enzymes in the pathway contrasts with efforts for drugging similarly common PTMs such as phosphorylation and acetylation, which are routinely studied and targeted in relevant cancer contexts. Here, we review recent advances in identifying targetable protein lipidation pathways in cancer, the current state-of-the-art in drug discovery, and the status of ongoing clinical trials, which have the potential to deliver novel oncology therapeutics targeting protein lipidation.

Immunogenic Bifunctional Nanoparticle Suppresses Programmed Cell Death-Ligand 1 in Cancer and Dendritic Cells to Enhance Adaptive Immunity and Chemo-Immunotherapy

Blockade of programmed cell death-1/programmed cell death-ligand 1 (PD-L1) immune checkpoints with monoclonal antibodies has shown great promise for cancer treatment, but these antibodies can cause immune-related adverse events in normal organs. Here we report a dual-cell targeted chemo-immunotherapeutic nanoscale coordination polymer (NCP), OxPt/BP, comprising oxaliplatin (OxPt) and 2-bromopalmitic acid (BP), for effective downregulation of PD-L1 expression in both cancer cells and dendritic cells (DCs) by inhibiting palmitoyl acyltransferase DHHC3. OxPt/BP efficiently promotes DC maturation by increasing intracellular oxidative stress and enhancing OxPt-induced immunostimulatory immunogenic cancer cell death. Systemic administration of OxPt/BP reduces the growth of subcutaneous and orthotopic colorectal carcinoma by facilitating the infiltration and activation of cytotoxic T lymphocytes together with reducing the population of immunosuppressive regulatory T cells. As a result, OxPt/BP significantly extends mouse survival without causing side effects. This work highlights the potential of NCPs in simultaneously reprogramming cancer cells and DCs for potent cancer treatment.

Changes in miR-134-3p expression and zDHHC3-AMPARs axis in association with aluminum neurotoxicity

Aluminum (Al) is a neurotoxic substance associated with cognitive dysfunction and neurodegenerative diseases, such as Alzheimer's disease, but the mechanisms for aluminum neurotoxicity remain to be identified. In this work, we try to investigate a novel potential biomarker of cognitive dysfunction following aluminum exposure and the mechanism involved. Recently, miR-134-3p was reported as a novel regulator of cognitive function. To address this, we investigate the expression level of miR-134-3p in plasma from 280 aluminum factory workers and analyzed the correlation between miRNA-134-3p, blood Al concentration, and Montreal Cognitive Assessment Scale (MoCA scale) score. The results implied that occupational aluminum exposure elevated miR-134-3p expression in the plasma of workers accompanied by cognitive impairment. Our experiment studies using both animal models and PC12 cells validated the upregulation of miR-134-3p caused by aluminum. In addition, we identified that palmitoylation enzyme zDHHC3 was the target of miR-134-3p, and the decreasing AMPAR receptor (AMPAR) trafficking was related to the learning and memory impairment induced by aluminum. More importantly, using transfection and interference approaches in PC12 cells, inhibition of miR-134-3p resulted in a recovery of zDHHC3-AMPARs axis to a certain extent in response to aluminum. In summary, miR-134-3p was found to be involved in aluminum neurotoxicity by targeting zDHHC3-AMPARs axis and could serve as a potential biomarker or helpful target.

Advancements in Oncoproteomics Technologies: Treading toward Translation into Clinical Practice

Proteomics continues to forge significant strides in the discovery of essential biological processes, uncovering valuable information on the identity, global protein abundance, protein modifications, proteoform levels, and signal transduction pathways. Cancer is a complicated and heterogeneous disease, and the onset and progression involve multiple dysregulated proteoforms and their downstream signaling pathways. These are modulated by various factors such as molecular, genetic, tissue, cellular, ethnic/racial, socioeconomic status, environmental, and demographic differences that vary with time. The knowledge of cancer has improved the treatment and clinical management; however, the survival rates have not increased significantly, and cancer remains a major cause of mortality. Oncoproteomics studies help to develop and validate proteomics technologies for routine application in clinical laboratories for (1) diagnostic and prognostic categorization of cancer, (2) real-time monitoring of treatment, (3) assessing drug efficacy and toxicity, (4) therapeutic modulations based on the changes with prognosis and drug resistance, and (5) personalized medication. Investigation of tumor-specific proteomic profiles in conjunction with healthy controls provides crucial information in mechanistic studies on tumorigenesis, metastasis, and drug resistance. This review provides an overview of proteomics technologies that assist the discovery of novel drug targets, biomarkers for early detection, surveillance, prognosis, drug monitoring, and tailoring therapy to the cancer patient. The information gained from such technologies has drastically improved cancer research. We further provide exemplars from recent oncoproteomics applications in the discovery of biomarkers in various cancers, drug discovery, and clinical treatment. Overall, the future of oncoproteomics holds enormous potential for translating technologies from the bench to the bedside.

Protein palmitoylation in cancer: molecular functions and therapeutic potential

Protein S-palmitoylation (hereinafter referred to as protein palmitoylation) is a reversible lipid posttranslational modification catalyzed by the zinc finger DHHC-type containing (ZDHHC) protein family. The reverse reaction, depalmitoylation, is catalyzed by palmitoyl-protein thioesterases (PPTs), including acyl-protein thioesterases (APT1/2), palmitoyl protein thioesterases (PPT1/2), or alpha/beta hydrolase domain-containing protein 17A/B/C (ABHD17A/B/C). Proteins encoded by several oncogenes and tumor suppressors are modified by palmitoylation, which enhances the hydrophobicity of specific protein subdomains, and can confer changes in protein stability, membrane localization, protein-protein interaction, and signal transduction. The importance for protein palmitoylation in tumorigenesis has just started to be elucidated in the past decade; palmitoylation appears to affect key aspects of cancer, including cancer cell proliferation and survival, cell invasion and metastasis, and antitumor immunity. Here we review the current literature on protein palmitoylation in the various cancer types, and discuss the potential of targeting of palmitoylation enzymes or palmitoylated proteins for tumor treatment.

Structural Exploration on Palmitoyltransferase DHHC3 from Homo sapiens

DHHC3 belongs to a family of DHHC palmitoyltransferase, which catalyzes the S-palmitoylation of target proteins by attaching a fatty acyl group to a cysteine. Recently, DHHC3 has been demonstrated to be a promising antitumor target in cancer therapeutics. However, the detailed structure and catalysis mechanism of DHHC3 remain elusive, considering its sequence diversity from the DHHC homologues with known crystal structures. Here, we described the expression and purification of human DHHC3 (hDHHC3) and truncated hDHHC3 with the flexible N-terminal domain (NTD) removed. Purified hDHHC3 proteins were used under various conditions for protein crystallization. LAMTOR1, one of the interacting proteins of hDHHC3 to facilitate the crystallization, was further identified by mass spectrometry and co-immunoprecipitation assay. The structural exploration using cryogenic electronic microscopy (cryo-EM) on the inactive hDHHS3 mutant showed a typical sideview of membrane proteins. These results provide a preliminary guidance for the structural determination of DHHC3.

Antioxidant and Anticancer Functions of Protein Acyltransferase DHHC3

Silencing of DHHC3, an acyltransferase enzyme in the DHHC family, extensively upregulates oxidative stress (OS). Substrates for DHHC3-mediated palmitoylation include several antioxidant proteins and many other redox regulatory proteins. This helps to explain why DHHC3 ablation upregulates OS. DHHC3 also plays a key role in cancer. DHHC3 ablation leads to diminished xenograft growth of multiple cancer cell types, along with diminished metastasis. Furthermore, DHHC3 protein is upregulated on malignant/metastatic cancer samples, and upregulated gene expression correlates with diminished patient survival in several human cancers. Decreased primary tumor growth due to DHHC3 ablation may be partly explained by an elevated OS → senescence → innate immune cell recruitment mechanism. Elevated OS due to DHHC3 ablation may also contribute to adaptive anticancer immunity and impair tumor metastasis. In addition, DHHC3 ablation disrupts antioxidant protection mechanisms, thus enhancing the efficacy of OS-inducing anticancer drugs. A major focus has thus far been on OS regulation by DHHC3. However, remaining to be studied are multiple DHHC3 substrates that may affect tumor behavior independent of OS. Nonetheless, the currently established properties of DHHC3 make it an attractive candidate for therapeutic targeting in situations in which antioxidant protections need to be downmodulated, and also in cancer.

Recent progress of palmitoyl transferase DHHC3 as a novel antitumor target

DHHC3 is a DHHC-family palmitoyl acyltransferase that is responsible for many mammalian palmitoylation events. By regulating the posttranslational modification of its specific substrates, DHHC3 has shown a strong protumor effect in various cancers. In this review, the authors introduce the research progress of DHHC3 as a new antitumor target through the expression of DHHC3 in patients with tumors, substrate proteins and potential mechanisms. Recent advances in the search for protein structures and inhibitors are also reviewed. Several design strategies to facilitate the optimization of the process of drug design based on DHHC3 are also discussed.

On the Road to Accurate Protein Biomarkers in Prostate Cancer Diagnosis and Prognosis: Current Status and Future Advances

Prostate cancer (PC) is a leading cause of morbidity and mortality among men worldwide. Molecular biomarkers work in conjunction with existing clinicopathologic tools to help physicians decide who to biopsy, re-biopsy, treat, or re-treat. The past decade has witnessed the commercialization of multiple PC protein biomarkers with improved performance, remarkable progress in proteomic technologies for global discovery and targeted validation of novel protein biomarkers from clinical specimens, and the emergence of novel, promising PC protein biomarkers. In this review, we summarize these advances and discuss the challenges and potential solutions for identifying and validating clinically useful protein biomarkers in PC diagnosis and prognosis. The identification of multi-protein biomarkers with high sensitivity and specificity, as well as their integration with clinicopathologic parameters, imaging, and other molecular biomarkers, bodes well for optimal personalized management of PC patients.

Discovery of a Dual Tubulin and Poly(ADP-Ribose) Polymerase-1 Inhibitor by Structure-Based Pharmacophore Modeling, Virtual Screening, Molecular Docking, and Biological Evaluation

Dual inhibition of tubulin and poly(ADP-ribose) polymerase-1 (PARP-1) may become an attractive approach for cancer therapy. Here, we discover a dual tubulin/PARP-1 inhibitor (termed as TP-3) using structure-based virtual screening. TP-3 shows strong dual inhibitory effects on both tubulin and PARP-1. Cellular assays reveal that TP-3 shows superior antiproliferative activities against human cancer cells, including breast, liver, ovarian, and cervical cancers. Further studies indicate that TP-3 plays an antitumor role through multiple mechanisms, including the disturbance of the microtubule network and the PARP-1 DNA repairing function, accumulation of DNA double-strand breaks, inhibition of the tube formation, and induction of G2/M cell cycle arrest and apoptosis. In vivo assessment indicates that TP-3 inhibits the growth of MDA-MB-231 xenograft tumors in nude mouse with no notable side effects. These data demonstrate that TP-3 is a dual-targeting, high-efficacy, and low-toxic antitumor agent.

Post-Translational Modifications That Drive Prostate Cancer Progression

While a protein primary structure is determined by genetic code, its specific functional form is mostly achieved in a dynamic interplay that includes actions of many enzymes involved in post-translational modifications. This versatile repertoire is widely used by cells to direct their response to external stimuli, regulate transcription and protein localization and to keep proteostasis. Herein, post-translational modifications with evident potency to drive prostate cancer are explored. A comprehensive list of proteome-wide and single protein post-translational modifications and their involvement in phenotypic outcomes is presented. Specifically, the data on phosphorylation, glycosylation, ubiquitination, SUMOylation, acetylation, and lipidation in prostate cancer and the enzymes involved are collected. This type of knowledge is especially valuable in cases when cancer cells do not differ in the expression or mutational status of a protein, but its differential activity is regulated on the level of post-translational modifications. Since their driving roles in prostate cancer, post-translational modifications are widely studied in attempts to advance prostate cancer treatment. Current strategies that exploit the potential of post-translational modifications in prostate cancer therapy are presented.