Isoprenylcysteine carboxyl methyltransferase (ICMT) promotes invadopodia formation and metastasis in cancer cells.

Isoprenyl cysteine carboxyl methyltransferase (ICMT) catalyzes the last step of the prenylation pathway. Previously, we found that high ICMT levels enhance tumorigenesis in vivo and that its expression is repressed by the p53 tumor suppressor. Based on evidence suggesting that some ICMT substrates affect invasive traits, we wondered if this enzyme may promote metastasis. In this work, we found that ICMT overexpression enhanced lung metastasis in vivo. Accordingly, ICMT overexpression also promoted cellular functions associated with aggressive phenotypes such as migration and invasion in vitro. Considering that some ICMT substrates are involved in the regulation of actin cytoskeleton, we hypothesized that actin-rich structures, associated with invasion and metastasis, may be affected. Our findings revealed that ICMT enhanced the formation of invadopodia. Additionally, by analyzing cancer patient databases, we found that ICMT is overexpressed in several tumor types. Furthermore, the concurrent expression of ICMT and CTTN, which encodes a crucial component of invadopodia, showed a significant correlation with clinical outcome. In summary, our work identifies ICMT overexpression as a relevant alteration in human cancer that promotes the development of metastatic tumors.

Distinct specificities of the HEMK2 protein methyltransferase in methylation of glutamine and lysine residues.

The HEMK2 protein methyltransferase has been described as glutamine methyltransferase catalyzing ERF1-Q185me1 and lysine methyltransferase catalyzing H4K12me1. Methylation of two distinct target residues is unique for this class of enzymes. To understand the specific catalytic adaptations of HEMK2 allowing it to master this chemically challenging task, we conducted a detailed investigation of the substrate sequence specificities of HEMK2 for Q- and K-methylation. Our data show that HEMK2 prefers methylation of Q over K at peptide and protein level. Moreover, the ERF1 sequence is strongly preferred as substrate over the H4K12 sequence. With peptide SPOT array methylation experiments, we show that Q-methylation preferentially occurs in a G-Q-X3 -R context, while K-methylation prefers S/T at the first position of the motif. Based on this, we identified novel HEMK2 K-methylation peptide substrates with sequences taken from human proteins which are methylated with high activity. Since H4K12 methylation by HEMK2 was very low, other protein lysine methyltransferases were examined for their ability to methylate the H4K12 site. We show that SETD6 has a high H4K12me1 methylation activity (about 1000-times stronger than HEMK2) and this enzyme is mainly responsible for H4K12me1 in DU145 prostate cancer cells.

The Role of Protein Methyltransferases in Immunity.

The immune system protects our body from bacteria, viruses, and toxins and removes malignant cells. Activation of immune cells requires the onset of a network of important signaling proteins. Methylation of these proteins affects their structure and biological function. Under stimulation, T cells, B cells, and other immune cells undergo activation, development, proliferation, differentiation, and manufacture of cytokines and antibodies. Methyltransferases alter the above processes and lead to diverse outcomes depending on the degree and type of methylation. In the previous two decades, methyltransferases have been reported to mediate a great variety of immune stages. Elucidating the roles of methylation in immunity not only contributes to understanding the immune mechanism but is helpful in the development of new immunotherapeutic strategies. Hence, we review herein the studies on methylation in immunity, aiming to provide ideas for new approaches.

DNA and protein methyltransferases inhibition by adenosine dialdehyde reduces the proliferation and migration of breast and lung cancer cells by downregulating autophagy.

Protein and DNA methylation is involved in various biological functions such as signal transmission, DNA repair, and gene expression. Abnormal regulation of methyltransferases has been linked to multiple types of cancer, but its link to autophagy and carcinogenesis in breast and lung cancer is not fully understood. We utilized UALCAN, a web tool, to investigate breast and lung cancer database from The Cancer Genome Atlas. We found that 17 methyltransferases are upregulated in breast and/or lung cancer. We investigated the effect of methylation inhibition on two breast cancer cell lines (MDA-MB-231 and MCF-7) and two lung cancer cell lines (H292 and A549) by treating them with the indirect methyltransferase inhibitor adenosine dialdehyde (AdOx). We found that the migration ability of all cell lines was decreased, and the growth rate of MDA-MB-231, MCF-7 and H292 was also decreased after AdOx treatment. These results were correlated with an inhibition of the autophagy in MDA-MB-231, MCF-7 and H292 cell lines, since AdOx treatment induced a decreased expression of ATG7, a reduced ratio LC3-II/LC3-I and an increased p62 level. These findings suggest that inhibiting cells' methylation ability could be a potential target for breast and lung cancer treatment.

Characterization of the biochemical activity and tumor-promoting role of the dual protein methyltransferase METL-13/METTL13 in Caenorhabditis elegans.

The methyltransferase-like protein 13 (METTL13) methylates the eukaryotic elongation factor 1 alpha (eEF1A) on two locations: the N-terminal amino group and lysine 55. The absence of this methylation leads to reduced protein synthesis and cell proliferation in human cancer cells. Previous studies showed that METTL13 is dispensable in non-transformed cells, making it potentially interesting for cancer therapy. However, METTL13 has not been examined yet in whole animals. Here, we used the nematode Caenorhabditis elegans as a simple model to assess the functions of METTL13. Using methyltransferase assays and mass spectrometry, we show that the C. elegans METTL13 (METL-13) methylates eEF1A (EEF-1A) in the same way as the human protein. Crucially, the cancer-promoting role of METL-13 is also conserved and depends on the methylation of EEF-1A, like in human cells. At the same time, METL-13 appears dispensable for animal growth, development, and stress responses. This makes C. elegans a convenient whole-animal model for studying METL13-dependent carcinogenesis without the complications of interfering with essential wild-type functions.

Construction and validation of a prognostic model based on ten signature cell cycle-related genes for early-stage lung squamous cell carcinoma.

BACKGROUND: We performed a bioinformatics analysis to screen for cell cycle-related differentially expressed genes (DEGs) and constructed a model for the prognostic prediction of patients with early-stage lung squamous cell carcinoma (LSCC). METHODS: From a gene expression omnibus (GEO) database, the GSE157011 dataset was randomly divided into an internal training group and an internal testing group at a 1:1 ratio, and the GSE30219, GSE37745, GSE42127, and GSE73403 datasets were merged as the external validation group. We performed single-sample gene set enrichment analysis (ssGSEA), univariate Cox analysis, and difference analysis, and identified 372 cell cycle-related genes. Additionally, we combined LASSO/Cox regression analysis to construct a prognostic model. Then, patients were divided into high-risk and low-risk groups according to risk scores. The internal testing group, discovery set, and external verification set were used to assess model reliability. We used a nomogram to predict patient prognoses based on clinical features and risk values. Clinical relevance analysis and the Human Protein Atlas (HPA) database were used to verify signature gene expression. RESULTS: Ten cell cycle-related DEGs (EIF2B1, FSD1L, FSTL3, ORC3, HMMR, SETD6, PRELP, PIGW, HSD17B6, and GNG7) were identified and a model based on the internal training group constructed. From this, patients in the low-risk group had a higher survival rate when compared with the high-risk group. Time-dependent receiver operating characteristic (tROC) and Cox regression analyses showed the model was efficient and accurate. Clinical relevance analysis and the HPA database showed that DEGs were significantly dysregulated in LSCC tissue. CONCLUSION: Our model predicted the prognosis of early-stage LSCC patients and demonstrated potential applications for clinical decision-making and individualized therapy.

Human seven-ß-strand (METTL) methyltransferases - conquering the universe of protein lysine methylation.

Lysine methylation is an abundant posttranslational modification, which has been most intensively studied in the context of histone proteins, where it represents an important epigenetic mark. Lysine methylation of histone proteins is primarily catalyzed by SET-domain methyltransferases (MTases). However, it has recently become evident that also another MTase family, the so-called seven-ß-strand (7BS) MTases, often denoted METTLs (methyltransferase-like), contains several lysine (K)-specific MTases (KMTs). These enzymes catalyze the attachment of up to three methyl groups to lysine residues in specific substrate proteins, using S-adenosylmethionine (AdoMet) as methyl donor. About a decade ago, only a single human 7BS KMT was known, namely the histone-specific DOT1L, but 15 additional 7BS KMTs have now been discovered and characterized. These KMTs typically target a single nonhistone substrate that, in most cases, belongs to one of the following three protein groups: components of the cellular protein synthesis machinery, mitochondrial proteins, and molecular chaperones. This article provides an extensive overview and discussion of the human 7BS KMTs and their biochemical and biological roles.

STC2 activates PRMT5 to induce radioresistance through DNA damage repair and ferroptosis pathways in esophageal squamous cell carcinoma.

Radioresistance is the major reason for the failure of radiotherapy in esophageal squamous cell carcinoma (ESCC). Previous evidence indicated that stanniocalcin 2 (STC2) participates in various biological processes of malignant tumors. However, researches on its effect on radioresistance in cancers are limited. In this study, STC2 was screened out by RNA-sequencing and bioinformatics analyses as a potential prognosis predictor of ESCC radiosensitivity and then was determined to facilitate radioresistance. We found that STC2 expression is increased in ESCC tissues compared to adjacent normal tissues, and a higher level of STC2 is associated with poor prognosis. Also, STC2 mRNA and protein expression levels were higher in radioresistant cells than in their parental cells. Further investigation revealed that STC2 could interact with protein methyltransferase 5 (PRMT5) and activate PRMT5, thus leading to the increased expression of symmetric dimethylation of histone H4 on Arg 3 (H4R3me2s). Mechanistically, STC2 can promote DDR through the homologous recombination and non-homologous end joining pathways by activating PRMT5. Meanwhile, STC2 can participate in SLC7A11-mediated ferroptosis in a PRMT5-dependent manner. Finally, these results were validated through in vivo experiments. These findings uncovered that STC2 might be an attractive therapeutic target to overcome ESCC radioresistance.

Investigating the functional role of SETD6 in lung adenocarcinoma.

BACKGROUND: SET domain containing 6 (SETD6) has been shown to be upregulated in multiple human cancers and can promote malignant cell survival. However, expression and function of SETD6 in lung adenocarcinoma (LUAD) remains unaddressed. This study aimed to demonstrate the expression pattern, biological roles and potential mechanisms by which SETD6 dysregulation is associated with LUAD. METHODS: The expression level of SETD6 was evaluated in LUAD clinical specimens and its correlation with clinical parameters were analyzed. In vitro, gain-of-function and loss-of-function experiments were performed to evaluate the effects of SETD6 on cell proliferation, apoptosis, migration, and colony formation of LUAD cell line A549. Western-blot was performed to investigate the involvement of nuclear factor-κB (NF-κB) and nuclear factor erythroid 2-related factor 2 (Nrf2) pathways as downstream signaling of SETD6 in LUAD cells. RESULTS: Compared with non-tumorous tissues, SETD6 was overexpressed in tumor tissues, and its overexpression significantly correlates with higher rates of regional lymph node metastasis and poor prognosis in patients with LUAD. In A549 cell line, SETD6 overexpression could promote cell proliferation, migration, colony formation and inhibit cell apoptosis, whereas SETD6 knockdown caused the opposite effects. Furthermore, we demonstrated that the mechanisms underlying the effect of SETD6 on LUAD biological behaviors may be through its interaction with NF-κB and Nrf2 signaling pathways. CONCLUSIONS: SETD6, which is highly expressed in LUAD tumor tissues, plays an important role in promoting the malignant behaviors of LUAD via likely the NF-κB and Nrf2 signaling pathways.

SETD6 Regulates E2-Dependent Human Papillomavirus Transcription.

Bromodomain-containing protein 4 (Brd4) is a member of the bromodomain and extraterminal domain (BET) family of proteins. Brd4 regulates human papillomavirus (HPV) transcription, genome replication, and segregation by binding to the E2 protein. The SETD6 methyltransferase binds to and methylates Brd4 at lysine 99. We investigated the interactions of SETD6 and Brd4 with E2 and their role in HPV transcription. SETD6 coimmunoprecipitated with the E2 transactivation domain, and its depletion in CIN612 episomal cells reduced human papillomavirus type 31 (HPV-31) transcription, whereas depletion of SETD6 in integrated HPV cell lines had no effect on viral gene expression. The mutant Brd4 K99R (bearing a change of K to R at position 99), which cannot be methylated by SETD6, displayed decreased binding to HPV-31 E2, suggesting that SETD6 methylation of Brd4 also influences E2 association with the Brd4 protein. Using chromatin immunoprecipitation, SETD6 was detected at the enhancer region of the HPV long control region. We propose that methylation of Brd4 at K99 by SETD6 is an important mechanism for E2-Brd4 association and HPV transcriptional activation. IMPORTANCE Human papillomaviruses (HPV) cause cervical, anogenital, and oral cancers. Brd4 plays an important role in the HPV life cycle. SETD6 was recently shown to methylate Brd4. The current study demonstrates that methylation of Brd4 by SETD6 in HPV-episomal cells is required for the activation of viral transcription. This study illustrates a novel regulatory mechanism involving E2, Brd4, and SETD6 in the HPV life cycle and provides insight into the multiple roles of Brd4 in viral pathogenesis.

A novel immune-related epigenetic signature based on the transcriptome for predicting the prognosis and therapeutic response of patients with diffuse large B-cell lymphoma.

Epigenetic modifications contribute to lymphomagenesis. Here, we performed an expression clustering analysis and identified two epigenetic-related clusters (EC1 and EC2). EC1 presented abundant TP53, MYD88, HIST1H1D, HIST1H1C, KMT2D and EZH2 mutations and an inferior prognosis. Pathways involved in the regulation of DNA methylation/demethylation, histone methyltransferase activity, and protein methyltransferase activity were significantly enriched in EC1. However, EC2 was frequently accompanied by B2M, CD70 and MEF2B mutations, which presented with enrichments in DNA damage repair, cytokine-mediated and B-cell activated immune signaling, increased levels of CD8+ T-, γδT- and T helper-cells, as well as immune scores and immunogenic cell death (ICD) modulators. According to the prediction, EC1 was more sensitive to vorinostat, serdemetan and navitoclax. However, ruxolitinib, cytarabine and CP466722 were more suitable treatments for EC2. The novel immune-related epigenetic signature exhibits promising clinical predictive value for diffuse large B-cell lymphoma (DLBCL), particularly for guiding epigenetic therapeutic regimens. R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone) based combination treatment regimens are suggested.

PFKFB4 interacts with ICMT and activates RAS/AKT signaling-dependent cell migration in melanoma.

Cell migration is a complex process, tightly regulated during embryonic development and abnormally activated during cancer metastasis. RAS-dependent signaling is a major nexus controlling essential cell parameters including proliferation, survival, and migration, utilizing downstream effectors such as the PI3K/AKT signaling pathway. In melanoma, oncogenic mutations frequently enhance RAS, PI3K/AKT, or MAP kinase signaling and trigger other cancer hallmarks among which the activation of metabolism regulators. PFKFB4 is one of these critical regulators of glycolysis and of the Warburg effect. Here, however, we explore a novel function of PFKFB4 in melanoma cell migration. We find that PFKFB4 interacts with ICMT, a posttranslational modifier of RAS. PFKFB4 promotes ICMT/RAS interaction, controls RAS localization at the plasma membrane, activates AKT signaling and enhances cell migration. We thus provide evidence of a novel and glycolysis-independent function of PFKFB4 in human cancer cells. This unconventional activity links the metabolic regulator PFKFB4 to RAS-AKT signaling and impacts melanoma cell migration.

TWIST1 methylation by SETD6 selectively antagonizes LINC-PINT expression in glioma.

Gliomas are one of the most common and lethal brain tumors among adults. One process that contributes to glioma progression and recurrence is the epithelial to mesenchymal transition (EMT). EMT is regulated by a set of defined transcription factors which tightly regulate this process, among them is the basic helix-loop-helix family member, TWIST1. Here we show that TWIST1 is methylated on lysine-33 at chromatin by SETD6, a methyltransferase with expression levels correlating with poor survival in glioma patients. RNA-seq analysis in U251 glioma cells suggested that both SETD6 and TWIST1 regulate cell adhesion and migration processes. We further show that TWIST1 methylation attenuates the expression of the long-non-coding RNA, LINC-PINT, thereby promoting EMT in glioma. Mechanistically, TWIST1 methylation represses the transcription of LINC-PINT by increasing the occupancy of EZH2 and the catalysis of the repressive H3K27me3 mark at the LINC-PINT locus. Under un-methylated conditions, TWIST1 dissociates from the LINC-PINT locus, allowing the expression of LINC-PINT which leads to increased cell adhesion and decreased cell migration. Together, our findings unravel a new mechanistic dimension for selective expression of LINC-PINT mediated by TWIST1 methylation.

Specificity Analysis of Protein Methyltransferases and Discovery of Novel Substrates Using SPOT Peptide Arrays.

Posttranslational methylation of amino acid side chains in proteins mainly occurs on lysine, arginine, glutamine, and histidine residues. It is introduced by different protein methyltransferases (PMTs) and regulates many aspects of protein function including stability, activity, localization, and protein/protein interactions. Although the biological effects of PMTs are mediated by their methylation substrates, the full substrate spectrum of most PMTs is not known. For many PMTs, their activity on a particular potential substrate depends, among other factors, on the peptide sequence containing the target residue for methylation. In this protocol, we describe the application of SPOT peptide arrays to investigate the substrate specificity of PMTs and identify novel substrates. Methylation of SPOT peptide arrays makes it possible to study the methylation of many different peptides in one experiment at reasonable costs and thereby provides detailed information about the specificity of the PMT under investigation. In these experiments, a known substrate sequence is used as template to design a SPOT peptide array containing peptides with single amino acid exchanges at all positions of the sequence. Methylation of the array with the PMT provides detailed preferences for each amino acid at each position in the substrate sequence, yielding a substrate sequence specificity profile. This information can then be used to identify novel potential PMT substrates by in silico data base searches. Methylation of novel substrate candidates can be validated in SPOT arrays at peptide level, followed by validation at protein level in vitro and in cells.

CircRNA hsa_circ_0018289 exerts an oncogenic role in cervical cancer progression through miR-1294/ICMT axis.

BACKGROUND: circRNA hsa_circ_0018289-mediated growth and metastasis of CC cells were investigated, as well as the mechanistic pathway. METHODS: Quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) was carried out to examine the expression of hsa_circ_0018289, microRNA (miR)-1294, and isoprenylcysteine carboxyl methyltransferase (ICMT). CC cell proliferation, migration, and invasion were evaluated by 5-ethynyl-2'-deoxyuridine (EdU) incorporation, colony formation, transwell assays, Western blot analysis of ICMT, and glycolysis-associated proteins. Dual-luciferase reporter or RNA pull-down analysis of the target interaction between miR-1294 and hsa_hsa_circ_0018289 or ICMT. Xenograft model assay was implemented to assess the role of hsa_circ_0018289 in vivo. Immunofluorescence (IHC) was employed to detect the level of Ki-67. RESULTS: Hsa_circ_0018289 was elevated in CC tissues and cells, its deficiency could repress growth, metastasis, and glycolysis of CC cells in vitro, as well as hamper tumor growth in vivo. Hsa_circ_0018289 sponged miR-1294 while miR-1294 bound with ICMT, and the inhibition of miR-1294 or addition of ICMT could partially relieve the effect caused by hsa_circ_0018289 depletion. CONCLUSION: Hsa_circ_0018289 contributes to malignant development by regulating the miR-1294/ICMT axis, affording novel insight into CC therapy.

PRMT5 regulates ATF4 transcript splicing and oxidative stress response.

Protein methyltransferase 5 (PRMT5) symmetrically dimethylates arginine residues leading to regulation of transcription and splicing programs. Although PRMT5 has emerged as an attractive oncology target, the molecular determinants of PRMT5 dependency in cancer remain incompletely understood. Our transcriptomic analysis identified PRMT5 regulation of the activating transcription factor 4 (ATF4) pathway in acute myelogenous leukemia (AML). PRMT5 inhibition resulted in the expression of unstable, intron-retaining ATF4 mRNA that is detained in the nucleus. Concurrently, the decrease in the spliced cytoplasmic transcript of ATF4 led to lower levels of ATF4 protein and downregulation of ATF4 target genes. Upon loss of functional PRMT5, cells with low ATF4 displayed increased oxidative stress, growth arrest, and cellular senescence. Interestingly, leukemia cells with EVI1 oncogene overexpression demonstrated dependence on PRMT5 function. EVI1 and ATF4 regulated gene signatures were inversely correlated. We show that EVI1-high AML cells have reduced ATF4 levels, elevated baseline reactive oxygen species and increased sensitivity to PRMT5 inhibition. Thus, EVI1-high cells demonstrate dependence on PRMT5 function and regulation of oxidative stress response. Overall, our findings identify the PRMT5-ATF4 axis to be safeguarding the cellular redox balance that is especially important in high oxidative stress states, such as those that occur with EVI1 overexpression.

Isoprenylcysteine carboxyl methyltransferase is critical for glioblastoma growth and survival by activating Ras/Raf/Mek/Erk.

PURPOSE: The poor outcomes in glioblastoma necessitate new therapeutic target. Isoprenylcysteine carboxyl methyltransferase (ICMT), a unique enzyme of the final step of prenylation that modifies activities of oncogenic proteins, represents a promising target for many cancers. METHODS: Expression pattern, function and downstream pathway of ICMT in glioblastoma were analyzed using immunohistochemistry, ELISA, cellular assays and immunoblotting method. Combinatory effect was analyzed using Chou-Talalay approach. RESULTS: Upregulation of ICMT expression is a common phenomenon in glioblastoma patients regardless of clinicopathological characteristics. Gain-of-function and loss-of-function analysis support the role of ICMT in glioblastoma growth and survival but not migration. Importantly, pharmacological inhibitors of ICMT are effectively against glioblastoma cells while sparing normal neuron cells, and furthermore that they act synergistically with chemotherapeutic drugs. Consistently, ICMT inhibitor UCM-1336 significantly inhibits glioblastoma growth without causing toxicity in mice. Mechanistic studies demonstrate that Ras/Raf/Mek/Erk rather than Ras/PI3K/Akt/mTOR is the downstream pathway of ICMT-mediated glioblastoma growth. CONCLUSIONS: Our findings provide the proof-of-concept of pharmacologically targeting ICMT in the treatment of glioblastoma via deactivation of Ras/Raf/Mek/Erk.

How Protein Methylation Regulates Steroid Receptor Function.

Steroid receptors (SRs) are members of the nuclear hormonal receptor family, many of which are transcription factors regulated by ligand binding. SRs regulate various human physiological functions essential for maintenance of vital biological pathways, including development, reproduction, and metabolic homeostasis. In addition, aberrant expression of SRs or dysregulation of their signaling has been observed in a wide variety of pathologies. SR activity is tightly and finely controlled by post-translational modifications (PTMs) targeting the receptors and/or their coregulators. Whereas major attention has been focused on phosphorylation, growing evidence shows that methylation is also an important regulator of SRs. Interestingly, the protein methyltransferases depositing methyl marks are involved in many functions, from development to adult life. They have also been associated with pathologies such as inflammation, as well as cardiovascular and neuronal disorders, and cancer. This article provides an overview of SR methylation/demethylation events, along with their functional effects and biological consequences. An in-depth understanding of the landscape of these methylation events could provide new information on SR regulation in physiology, as well as promising perspectives for the development of new therapeutic strategies, illustrated by the specific inhibitors of protein methyltransferases that are currently available.

The duality of PRDM proteins: epigenetic and structural perspectives.

PRDF1 and RIZ1 homology domain containing (PRDMs) are a subfamily of Krüppel-like zinc finger proteins controlling key processes in metazoan development and in cancer. PRDMs exhibit unique dualities: (a) PR domain/ZNF arrays-their structure combines a SET-like domain known as a PR domain, typically found in methyltransferases, with a variable array of C2H2 zinc fingers (ZNF) characteristic of DNA-binding transcription factors; (b) transcriptional activators/repressors-their physiological function is context- and cell-dependent; mechanistically, some PRDMs have a PKMT activity and directly catalyze histone lysine methylation, while others are rather pseudomethyltransferases and act by recruiting transcriptional cofactors; (c) oncogenes/tumor suppressors-their pathological function depends on the specific PRDM isoform expressed during tumorigenesis. This duality is well known as the 'Yin and Yang' of PRDMs and involves a complex regulation of alternative splicing or alternative promoter usage, to generate full-length or PR-deficient isoforms with opposing functions in cancer. In conclusion, once their dualities are fully appreciated, PRDMs represent a promising class of targets in oncology by virtue of their widespread upregulation across multiple tumor types and their somatic dispensability, conferring a broad therapeutic window and limited toxic side effects. The recent discovery of a first-in-class compound able to inhibit PRDM9 activity has paved the way for the identification of further small molecular inhibitors able to counteract PRDM oncogenic activity.

Isoprenylcysteine carboxyl methyltransferase promotes the progression of tongue squamous cell carcinoma via the K-Ras and RhoA signaling pathways.

OBJECTIVE: This research investigated the biological role of isoprenylcysteine carboxyl methyltransferase (ICMT) in tongue squamous cell carcinoma (TSCC) progression meanwhile to explore the conceivable mechanism. METHODS: The mRNA and protein expression were measured using real-time PCR and Western blot. Cell proliferation, apoptosis, cycle distribution, migration and invasion were evaluated by CCK-8 assay, flow cytometry, wound-healing assay and transwell assay. The anti-tumor activity of ICMT silencing was observed in nude mice. RESULTS: Our results indicated that silencing of ICMT-mediated methylation effectively inhibited TSCC cells proliferation in vitro and reduced tumor growth in vivo. Moreover, ICMT knockdown also induced cell apoptosis and cell cycle arrest of both CAL-27 and SCC-4 cells. In addition, CAL-27 and SCC-4 cells migration and invasion were weakened by ICMT siRNA. Mechanistically, ICMT deficiency significantly decreased the K-Ras and RhoA membrane targeting localization, leading to the suppression of K-Ras- and RhoA-mediated downstream signaling in CAL-27 and SCC-4 cells. CONCLUSIONS: Altogether, our findings identified a crucial role played by ICMT in the progression of TSCC and the potential mechanisms by which exerted its effects, indicating that targeting ICMT may represent a promising therapeutic strategy for TSCC.