Identification of a structural motif in the tumor-suppressive protein GRIM-19 required for its antitumor activity

CIGB-300-Regulated Proteome Reveals Common and Tailored Response Patterns of AML Cells to CK2 Inhibition

Protein kinase CK2 is a highly pleiotropic and ubiquitously expressed Ser/Thr kinase with instrumental roles in normal and pathological states, including neoplastic phenotype in solid tumor and hematological malignancies. In line with previous reports, CK2 has been suggested as an attractive prognostic marker and molecular target in acute myeloid leukemia (AML), a blood malignant disorder that remains as an unmet medical need. Accordingly, this work investigates the complex landscape of molecular and cellular perturbations supporting the antileukemic effect exerted by CK2 inhibition in AML cells. To identify and functionally characterize the proteomic profile differentially modulated by the CK2 peptide-based inhibitor CIGB-300, we carried out LC-MS/MS and bioinformatic analysis in human cell lines representing two differentiation stages and major AML subtypes. Using this approach, 109 and 129 proteins were identified as significantly modulated in HL-60 and OCI-AML3 cells, respectively. In both proteomic profiles, proteins related to apoptotic cell death, cell cycle progression, and transcriptional/translational processes appeared represented, in agreement with previous results showing the impact of CIGB-300 in AML cell proliferation and viability. Of note, a group of proteins involved in intracellular redox homeostasis was specifically identified in HL-60 cell-regulated proteome, and flow cytometric analysis also confirmed a differential effect of CIGB-300 over reactive oxygen species (ROS) production in AML cells. Thus, oxidative stress might play a relevant role on CIGB-300-induced apoptosis in HL-60 but not in OCI-AML3 cells. Importantly, these findings provide first-hand insights concerning the CIGB-300 antileukemic effect and draw attention to the existence of both common and tailored response patterns triggered by CK2 inhibition in different AML backgrounds, a phenomenon of particular relevance with regard to the pharmacologic blockade of CK2 and personalized medicine.

Heterogeneity of GRIM-19 Expression in the Adult Mouse Brain

Gene associated with retinoid-interferon-induced mortality-19 (GRIM-19) is a subunit of the mitochondrial respiratory chain complex I that has a significant effect on ATP production. The brain is particularly susceptible to ATP deficiency due to its limited energy storage capability and its high rate of oxygen consumption. Thus, GRIM-19 might be involved in regulating ATP level in the brain or cell death caused by several neurological disorders. To understand the physiological and pathophysiological roles of GRIM-19 in the brain, a thorough investigation of the neuroanatomic distribution of GRIM-19 in the normal brain is necessary. Therefore, the present study examined the distribution patterns of GRIM-19 in the adult C57BL/6 mouse brain using immunohistochemistry and identified cell types expressing GRIM-19 using double immunofluorescence staining. We found that GRIM-19 was ubiquitously but not homogenously expressed throughout the brain. GRIM-19 immunoreactivity was predominantly observed in neurons, but not in astrocytes, microglia, or oligodendrocytes under normal physiological conditions. Following transient global cerebral ischemia, GRIM-19-positive immunoreactivity was, however, observed in neurons as well as glial cells including astrocytes in the hippocampus. Furthermore, GRIM-19 was weakly expressed in the hippocampal subgranular zone, in which neural stem and progenitor cells are abundant, but highly expressed in the immature and mature neuronal cells in the granular cell layer of the normal brain, suggesting an inverse correlation between expression of GRIM-19 and stemness activity. Collectively, our study demonstrating widespread and differential distribution of GRIM-19 in the adult mouse brain contributes to investigating the functional and pathophysiological roles of this protein.

GRIM-19: A master regulator of cytokine induced tumor suppression, metastasis and energy metabolism

Cytokines induce cell proliferation or growth suppression depending on the context. It is increasingly becoming clear that success of standard radiotherapy and/or chemotherapeutics to eradicate solid tumors is dependent on IFN signaling. In this review we discuss the molecular mechanisms of tumor growth suppression by a gene product isolated in our laboratory using a genome-wide expression knock-down strategy. Gene associated with retinoid-IFN-induced mortality -19 (GRIM-19) functions as non-canonical tumor suppressor by antagonizing oncoproteins. As a component of mitochondrial respiratory chain, GRIM-19 influences the degree of "Warburg effect" in cancer cells as many advanced and/or aggressive tumors show severely down-regulated GRIM-19 levels. In addition, GRIM-19 appears to regulate innate and acquired immune responses in mouse models. Thus, GRIM-19 is positioned at nodes that favor cell protection and/or prevent aberrant cell growth.

GRIM-19 Restores Cervical Cancer Cell Senescence by Repressing hTERT Transcription

High telomerase activity promotes tumor growth by stabilizing damaged chromosomes and their mitotic replication. Overactivation of telomerase activity has been reported in cervical cancer, a malignancy caused by high-risk human papillomaviruses (HR-HPVs). The HR-HPV E6 can activate hTERT promoter by interacting with E6AP or other binding proteins and by stabilizing the interaction between hTERT and E6AP. GRIM-19 is a novel tumor suppressor that affects multiple targets in a cell to regulate growth. We have previously reported the interaction of GRIM-19 with 18E6 and E6AP to disrupt the E6/E6AP complex and increase the autoubiquitination of E6AP. In this study, we characterized the interaction of GRIM-19 with 16E6 (an oncoprotein produced by HPV16) and identified the binding sites that mediate this interaction. We also found that GRIM-19 expression in cervical cancer cells could inhibit telomerase activity by inhibiting the transactivation of the hTERT promoter by E6, thereby promoting cervical cancer cell senescence. Moreover, we identified a negative correlation between GRIM-19 and hTERT expression in cervical cancer tissues. Suppression of GRIM-19 and induction of hTERT levels were associated with lymph node metastasis, advanced clinical stage, and poor prognosis. This study identified another important novel antitumor molecular link associated with GRIM-19 in the tumorigenesis.

Atrazine promotes RM1 prostate cancer cell proliferation by activating STAT3 signaling

Atrazine, a widely used pesticide, is frequently detected in soil and surface water, which alarms epidemiologists and medical professionals because of its potential deleterious effects on health. Indeed, atrazine is a potent endocrine disruptor that increases aromatase expression in some human cancer cell lines. Both animal and human studies have suggested that atrazine is possibly carcinogenic, although discrepant results have been reported. In this study, RM1 cells were used to explore the atrazine effects on prostate cancer. Proliferation, migration and invasion of RM1 cells were assessed by colony formation, wound-healing and invasion assays, respectively, after in vitro exposure to atrazine. In addition, an RM1 cell xenograft model was generated to evaluate the effects of atrazine in vivo. To explore the molecular mechanisms, qRT‑PCR, immunohistochemistry, and western blot analyses were employed to detect mRNA and protein levels of STAT3 signaling and cell cycle related proteins, including p53, p21, cyclin B1 and cyclin D1. Interestingly, RM1 cell proliferation was increased after treatment with atrazine, concomitantly with STAT3 signaling activation. These results suggest that atrazine promotes RM1 cell growth in vitro and in vivo by activating STAT3 signaling.

Molecular cloning and multifunctional characterization of GRIM-19 (gene associated with retinoid-interferon-induced mortality 19) homologue from turbot (Scophthalmus maximus)

GRIM-19 (gene associated with retinoid-interferon-induced mortality 19), a novel cell death regulatory gene, plays important roles in cell apoptosis, embryogenesis, mitochondrial respiratory chain and immune response. To date, little information is known about fish GRIM-19 characteristics except orange-spotted grouper (Epinephelus coioides). Here a new GRIM-19 gene is identified and characterized from turbot (Scophthalmus maximus), an economic marine fish in China and Europe. Briefly, turbot GRIM-19 is a 595-bp gene encoding a 144 amino acids protein, which shares the closest relationship with Atlantic halibut (Hippoglossus hippoglossus). The expression of turbot grim-19 in liver, spleen and kidney is up-regulated by the infection of Vibrio anguillarum and LCDV (lymphocystis disease virus). Subsequently, a recombinant protein of turbot GRIM-19 is acquired and the anti-bacterial function is proved by liquid culture inhibition experiment. The subcellular location indicates that turbot GRIM-19 is co-localized with STAT3 in the cytoplasm, which is mainly determined by GRIM-19 41-84 amino acids and STAT3 1-321 amino acids. Finally, the involvements of turbot GRIM-19 in cell apoptosis and NF-κB pathway are investigated. All these data help to understand GRIM-19 function in fish, as well as provide the application possibility of GRIM-19 in fish disease resistance breeding.

Tumor-derived mutations in the gene associated with retinoid interferon-induced mortality (GRIM-19) disrupt its anti-signal transducer and activator of transcription 3 (STAT3) activity and promote oncogenesis

The signal transducer and activator of transcription 3 (STAT3) protein is critical for multiple cytokine and growth factor-induced biological responses in vivo. Its transcriptional activity is controlled by a transient phosphorylation of a critical tyrosine. Constitutive activation of STAT3 imparts resistance to apoptosis, promotes cell proliferation, and induces de novo micro-angiogenesis, three of the six cardinal hallmarks of a typical cancer cell. Earlier we reported the isolation of GRIM-19 as a growth suppressor using a genome-wide expression knockdown strategy. GRIM-19 binds to STAT3 and suppresses its transcriptional activity. To understand the pathological relevance of GRIM-19, we screened a set of primary head and neck tumors and identified three somatic mutations in GRIM-19. Wild-type GRIM-19 suppressed cellular transformation by a constitutively active form of STAT3, whereas tumor-derived mutants L71P, L91P and A95T significantly lost their ability to associate with STAT3, block gene expression, and suppress cellular transformation and tumor growth in vivo. Additionally, these mutants lost their capacity to prevent metastasis. These mutations define a mechanism by which STAT3 activity is deregulated in certain human head and neck tumors.

GRIM-19-mediated translocation of STAT3 to mitochondria is necessary for TNF-induced necroptosis

Tumor necrosis factor (TNF) can induce necroptosis, wherein inhibition of caspase activity prevents apoptosis but initiates an alternative programmed necrosis. The activity of receptor-interacting serine/threonine-protein kinase 1 (RIPK-1) is required for necroptosis to proceed, with suppression of RIPK-1 expression or inhibition of RIPK-1 activity with necrostatin-1 preventing TNF-induced necroptosis. Downstream from the TNF receptor, the generation of reactive oxygen species at the mitochondria has been identified as necessary for the execution of necroptosis; with antioxidants and inhibitors of mitochondrial complex I preventing TNF-induced cytotoxicity. However, components of the signaling pathway that lie between activated RIPK-1 and the mitochondria are unknown. In the study reported here we demonstrate that during TNF-induced necroptosis, STAT3 is phosphorylated on serine 727, which is dependent on RIPK-1 expression or activity. The phosphorylation of STAT3 induces interaction with GRIM-19, a subunit of mitochondrial complex I, with a resultant translocation of STAT3 to the mitochondria, where it induces an increase in reactive oxygen species production and cell death.