Mitochondrial signatures shape phenotype switching and apoptosis in response to PLK1 and RSK inhibitiors in melanoma
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ABSTRACT: PLK1 inhibitors are emerging anti-cancer agents being tested in monotherapy and combination therapies for various cancers. Although PLK1 inhibition in experimental models shows potent antitumor effects, translation to the clinic has been hampered by low antitumor activity and tumor relapse. Here, we report the identification of mitochondrial protein signatures that determine sensitivity to approaches targeting PLK1 in human melanoma cell lines. In response to PLK1 inhibition or gene silencing, resistant cells adopt a pro-inflammatory and dedifferentiated phenotype, while sensitive cells engage apoptosis. Mitochondrial DNA depletion and silencing of the ABCD1 transporter sensitize cells to PLK1 inhibition and attenuate the associated pro-inflammatory response. We also found that non-selective inhibitors of the p90 ribosomal S6 kinase (RSK) exert their anti-proliferative and pro-inflammatory effects via PLK1 inhibition. This work reveals overlooked impacts of PLK1 on phenotype switching and suggests that mitochondrial precision medicine can help improve response to targeted therapies.
Project description:Saturated very long-chain fatty acids (VLCFA, ≥ C22), enriched in brain myelin and innate immune cells, accumulate in X-linked adrenoleukodystrophy (X-ALD). The severest form, inherited dysfunction of the VLCFA transporter ABCD1, underlying X-ALD, causes brain myelin destruction with infiltration of pro-inflammatory skewed monocytes/macrophages. How VLCFA levels relate to macrophage activation is unclear. Using whole transcriptome sequencing of X-ALD macrophages, we revealed that VLCFAs prime human macrophage membranes for inflammation and increase factors involved in chemotaxis and invasion. When applied externally, mimicking lipid destruction in X-ALD lesions, VLCFAs did not activate toll-like receptors in healthy cells but provoked pro-inflammatory responses through scavenger receptor CD36-mediated uptake, cumulating in JNK signalling and expression of matrix degrading enzymes and chemokine release. Following pro-inflammatory LPS-activation, VLCFA accumulated in healthy macrophages but were rapidly cleared with onset of resolution by increasing VLCFA degradation through liver-X-receptor mediated upregulation of ABCD1. ABCD1 deficiency impaired VLCFA homeostasis and prolonged pro-inflammatory gene expression. Our study uncovers a pivotal role for ABCD1, a protein linked to neuroinflammation, and associated peroxisomal VLCFA degradation in regulating macrophage plasticity.
Project description:Polo-like kinase 1 (PLK1) is a serine/threonine kinase required for mitosis and cytokinesis. As cancer cells are often hypersensitive to partial PLK1 inactivation, chemical inhibitors of PLK1 have been developed and tested in clinical trials. However, these molecules alone were not completely effective. PLK1 promotes numerous molecular and cellular events in the cell division cycle. To date, it is unclear which of these events most crucially depend on PLK1 activity. We used a CRISPR-based genome-wide screening strategy to identify genes whose inactivation enhances cell proliferation defects upon partial chemical inhibition of PLK1. Genes identified encode proteins that are functionally linked to PLK1 in multiple ways. Among them, factors that promote centromere and kinetochore function were clearly enriched. In particular, inactivation of the kinesin KIF18A or SKA1 in PLK1-compromised cells results in mitotic defects, activation of the spindle assembly checkpoint and nuclear reassembly defects. Our results suggest that functions of PLK1 at kinetochores are most sensitive to its inhibition, and point at KIF18A as a possible target for combinatorial therapies using existing PLK1 inhibitors.
Project description:Proteins from unrelated pathogens, including some RNA or DNA viruses and bacteria can recruit and activate cellular p90-ribosomal protein S6 kinases (RSKs) through a common linear motif. Data suggested a model where pathogens' proteins act to dock the recruited RSKs toward specific substrates, which then act as effectors to the benefit of the pathogens. Using cardiovirus leader protein (L) as a paradigm, we show that pathogens' proteins can modify the spectrum of RSK substrates in infected cells. L triggers nucleocytoplasmic trafficking perturbation and phenylalanine-glycine (FG)-nucleoporin hyperphosphorylation in an RSK-dependent fashion. Biotin ligase experiments identified FG-nucleoporins as common partners of L and RSK in infected cells. Using cells expressing an analog-sensitive RSK2 mutant, we show that L triggers direct phosphorylation of NUP98 and NUP214 by RSK2 in infected cells. Our data therefore demonstrate a novel virulence mechanism where pathogens' proteins hijack and retarget cellular protein kinases of the RSK family
Project description:RSK1 and RSK4 are two of the four members of the p90 ribosomal protein S6 kinases (RSK) family. These kinases are downstream kinases of mitogen-activated protein kinase 1 (ERK or MAPK1) in the ERK MAP kinase pathway. RSKs are implicated in fine tuning of cellular processes such as translation, transcription, proliferation, and motility. Previous work showed that pathogens such as Cardioviruses could hijack any of the four RSK isoforms to inhibit PKR activation or to disrupt cellular nucleocytoplasmic trafficking. In contrast, some reports suggest non-redundant functions for distinct RSK isoforms and Coffin-Lowry syndrome has only been associated with mutations in the gene encoding RSK2. In this work, we used the analog-sensitive kinase strategy to ask whether the cellular substrates of distinct RSK isoforms differ. We therefore compared the substrates of 2 of the most distant RSK isoforms: RSK1 and RSK4. We identified a series of potential substrates for both RSKs in cells, and validated RanBP3, PDCD4, IRS2 and ZC3H11A as substrates of both RSK1 and RSK4, and SORBS2 as a RSK1 substrate. In addition, using mutagenesis and inhibitors, we confirmed analog-sensitive kinase data showing that endogenous RSKs phosphorylate TRIM33 at S1119. Our data thus identify a series of potential RSK substrates and suggest that the substrates of RSK1 and RSK4 largely overlap and that the specificity of the various RSK isoforms likely depends on their cell- or tissue-specific expression pattern.
Project description:NK/T cell lymphoma (NKTCL) is a highly aggressive subtype of non-Hodgkin lymphoma. GELOX (gemcitabine, oxaliplatin, and L-asparaginase) is one of the first-line chemotherapy regimens of NKTCL. Yet, the prognosis of NKTCL is poor. Icaritin (ICT) is an herb-derived monomer from icariin with antitumor effects. We found that icaritin induced proliferation inhibition and apoptosis of NKTCL both in vitro and in vivo. Moreover, icaritin inhibited the dissemination of NKTCL in vivo. RNA sequencing (RNA-seq) revealed the polo-like kinase 1 (PLK1) gene and DNA damage response (DDR) as the targets of icaritin. Mechanistically, icaritin inhibited PLK1 to promote checkpoint kinase 2 (Chk2) homodimerization and its T387 phosphorylation, which further activated p53, leading to the activation of the DDR pathway. Moreover, inhibiting PLK1 increased Forkhead box O3a (FOXO3a) nuclear localization, the latter of which activated Ataxia-telangiectasia mutated (ATM), an early sensor of DNA damage. Then ATM phosphorylated Chk2 T68 and initiated Chk2 activation. Remarkably, combined treatment of icaritin and GELOX achieved better antitumor efficacy than single treatment in vivo. In summary, our results proved the efficacy of icaritin treating NKTCL, and provided insights into its antitumor molecular mechanism, and revealed the application value of icaritin in facilitating clinical NKTCL treatment.
Project description:Engineered T cells transiently expressing tumor-targeting receptors are an attractive form of engineered T cell therapy as they carry no risk of insertional mutagenesis or long-term adverse side-effects. However, multiple rounds of treatment are often required, increasing patient discomfort and cost. To mitigate this, we sought to improve the antitumor activity of transient engineered T cells by screening a panel of small molecules targeting epigenetic regulators for their effect on T cell cytotoxicity. Using a model for engineered T cells targetting hepatocellular carcinoma, we find that short-term inhibition of G9a/GLP increases T cell antitumor activity in in vitro models and an orthotopic mouse model. G9a/GLP inhibition increases granzyme expression without terminal T cell differentiation or exhaustion and results in specific changes in expression of genes and proteins involved in pro-inflammatory pathways, T cell activation and cytotoxicity.
Project description:The p90 ribosomal S6 kinase (RSK) family, a downstream target of Ras/extracellular signal-regulated kinase (ERK) signaling, can mediate cross-talk with the mammalian target of rapamycin complex 1 (mTORC1) pathway. As RSK connects two oncogenic pathways in gliomas, we investigated the protein levels of the RSK isoforms RSK1-4 in non-tumoral brain (NB) and grade I-IV gliomas. RSK4 expression was not detected in any brain tissues, whereas RSK3 expression was very low, with GBMs demonstrating the lowest RSK3 protein levels. When compared to NB or low-grade gliomas (LGG), a group of glioblastomas (RSK1hi) that excluded long-survivor cases expressed higher levels of RSK1. No difference was observed in RSK2 median-expression levels among NB and gliomas; however, high levels of RSK2 in glioblastomas (GBM) were associated with worse survival. RSK1hi and, to a lesser extent, RSK2hi GBMs, showed higher levels of phosphorylated RSK, which indicates RSK activation. Transcriptome analysis indicated that most RSK1hi GBMs belonged to the mesenchymal subtype, and RSK1 expression strongly correlated with gene expression signature of immune infiltrates, in particular of activated-natural killer cells and M2 macrophages. In an independent cohort, we confirmed that RSK1hi GBMs exclude long-survivors, and RSK1 expression was associated with high protein levels of the mesenchymal subtype marker LAPTM5, as well as with high expression of CD68, which indicated the presence of infiltrating immune cells. An RSK1 signature was obtained based on differentially expressed mRNAs and validated in public glioma datasets. Enrichment of RSK1 signature followed glioma progression, recapitulating RSK1 protein expression, and was associated with worse survival not only in GBM but also in LGG. In conclusion, both RSK1 and RSK2 associate with glioma malignity, but displaying isoform-specific peculiarities. The progression-dependent expression and association with immune infiltration, suggests RSK1 as a potential progression marker and therapeutic target for gliomas.
Project description:Fibrolamellar carcinoma (FLC), a rare and fatal liver cancer lacking effective drug therapy, is driven by the DNAJ-PKAc fusion oncoprotein. However, the underlying mechanism of DNAJ-PKAc's role in FLC tumor growth remains enigmatic. Employing an unbiased systems-based approach, we uncovered a new role of DNAJ-PKAc oncoprotein in FLC and identified downstream kinases involved in this process. Functional screening, coupled with computational analysis, highlighted Polo-like kinase 1 (PLK1) as vital for FLC cell viability. Genetic and pharmacological PLK1 inhibition significantly reduced FLC cell growth, inducing apoptosis. Further studies showed DNAJ-PKAc's centrosomal presence and direct interaction with PLK1, revealing a novel mechanism that promotes PLK1 activation and mitotic progression. Clinical-grade PLK1 inhibitors effectively suppressed FLC tumor growth across multiple preclinical models, including patient-derived xenograft and an orthotopic model of FLC, suggesting promising therapeutic avenues. Our findings underscore the role of DNAJ-PKAc in rewiring signaling networks and highlight valuable clinical implications for PLK1-targeted therapies for FLC.
Project description:Inhibitors of the mitotic kinase PLK1 yield objective responses in a subset of refractory cancers. However, PLK1 overexpression in cancer does not correlate with drug sensitivity, and the clinical development of PLK1 inhibitors has been hampered by the lack of patient selection marker. Using a high-throughput chemical screen, we discovered that cells deficient for the tumor suppressor ARID1A are highly sensitive to PLK1 inhibition. Interestingly this sensitivity was unrelated to canonical functions of PLK1 in mediating G2-M cell cycle transition. Instead, a whole-genome CRISPR screen revealed PLK1 inhibitor sensitivity in ARID1A deficient cells to be dependent on the mitochondrial translation machinery. We find that ARID1A knock-out (KO) cells have an unusual mitochondrial phenotype with aberrant biogenesis, increased oxygen consumption/ expression of oxidative phosphorylation genes, but without increased ATP production. Using expansion microscopy and biochemical fractionation, we see that a subset of PLK1 localizes to the mitochondria in interphase cells. Inhibition of PLK1 in ARID1A KO cells further uncouples oxygen consumption from ATP production, with subsequent membrane depolarization and apoptosis. Knockdown of specific subunits of the mitochondrial ribosome reverses PLK1-inhibitor induced apoptosis in ARID1A deficient cells, confirming specificity of the phenotype. Together, these findings highlight a novel interphase role for PLK1 in maintaining mitochondrial fitness under metabolic stress, and a strategy for therapeutic use of PLK1 inhibitors. To translate these findings, we describe a quantitative microscopy assay for assessment of ARID1A protein loss, which could offer a novel patient selection strategy for the clinical development of PLK1 inhibitors in cancer.