A transcriptional cross-talk between RhoA and c-Myc inhibits the RhoA/Rock-dependent cytoskeleton

Temporal myc dynamics permit mitotic bypass, promoting polyploid phenotypes

High Myc phenotypes are extensively documented in the hyperproliferative cell cycle of cancer cells, as well as non-proliferative endoreplication cycles engaged during normal development and stress response. Notably, endoreplication in cancer produces chemotherapy resistant polyploid cells, necessitating a clearer understanding of altered cell cycle regulation that uncouples DNA replication and mitotic cell division. The c-Myc oncogene is a well-established transcriptional regulator of cell cycle progression and has been extensively published as an essential driver of the G1/S transition. Beyond S phase, Myc transcriptionally activates the proteins that drive mitotic entry. Sustained activation of Myc through the cell cycle transcriptionally couples DNA replication and mitotic cell division. Based on the literature in this field, we propose a new model of temporal regulation of Myc activity that serves to either couple or uncouple these two processes, determining cell cycle fate - proliferation or polyploidy. The mitotic cell cycle requires two pulses of Myc activity - the first driving the G1/S transition and the second driving the G2/M transition. During mitosis, Myc activity must be silenced to achieve high-fidelity division. Absence of the second activity pulse during G2 results in the downregulation of the proteins essential for mitotic entry and permits premature activation of APC/C, inducing mitotic bypass. A subsequent rise of Myc activity following mitotic bypass permits genome re-replication, driving polyploid phenotypes. This model serves to provide a new level of understanding to the global regulation of S phase-mitosis coupling, as well as a new lens to view low Myc phenotypes.

MYC and KRAS cooperation: from historical challenges to therapeutic opportunities in cancer

RAS and MYC rank amongst the most commonly altered oncogenes in cancer, with RAS being the most frequently mutated and MYC the most amplified. The cooperative interplay between RAS and MYC constitutes a complex and multifaceted phenomenon, profoundly influencing tumor development. Together and individually, these two oncogenes regulate most, if not all, hallmarks of cancer, including cell death escape, replicative immortality, tumor-associated angiogenesis, cell invasion and metastasis, metabolic adaptation, and immune evasion. Due to their frequent alteration and role in tumorigenesis, MYC and RAS emerge as highly appealing targets in cancer therapy. However, due to their complex nature, both oncogenes have been long considered "undruggable" and, until recently, no drugs directly targeting them had reached the clinic. This review aims to shed light on their complex partnership, with special attention to their active collaboration in fostering an immunosuppressive milieu and driving immunotherapeutic resistance in cancer. Within this review, we also present an update on the different inhibitors targeting RAS and MYC currently undergoing clinical trials, along with their clinical outcomes and the different combination strategies being explored to overcome drug resistance. This recent clinical development suggests a paradigm shift in the long-standing belief of RAS and MYC "undruggability", hinting at a new era in their therapeutic targeting.

Balancing competing effects of tissue growth and cytoskeletal regulation during Drosophila wing disc development

How a developing organ robustly coordinates the cellular mechanics and growth to reach a final size and shape remains poorly understood. Through iterations between experiments and model simulations that include a mechanistic description of interkinetic nuclear migration, we show that the local curvature, height, and nuclear positioning of cells in the Drosophila wing imaginal disc are defined by the concurrent patterning of actomyosin contractility, cell-ECM adhesion, ECM stiffness, and interfacial membrane tension. We show that increasing cell proliferation via different growth-promoting pathways results in two distinct phenotypes. Triggering proliferation through insulin signaling increases basal curvature, but an increase in growth through Dpp signaling and Myc causes tissue flattening. These distinct phenotypic outcomes arise from differences in how each growth pathway regulates the cellular cytoskeleton, including contractility and cell-ECM adhesion. The coupled regulation of proliferation and cytoskeletal regulators is a general strategy to meet the multiple context-dependent criteria defining tissue morphogenesis.

Investigation of the impact of bromodomain inhibition on cytoskeleton stability and contraction

BACKGROUND

Injury to contractile organs such as the heart, vasculature, urinary bladder and gut can stimulate a pathological response that results in loss of normal contractility. PDGF and TGFβ are among the most well studied initiators of the injury response and have been shown to induce aberrant contraction in mechanically active cells of hollow organs including smooth muscle cells (SMC) and fibroblasts. However, the mechanisms driving contractile alterations downstream of PDGF and TGFβ in SMC and fibroblasts are incompletely understood, limiting therapeutic interventions.

METHODS

To identify potential molecular targets, we have leveraged the analysis of publicly available data, comparing transcriptomic changes in mechanically active cells stimulated with PDGF and TGFβ. Additional Analysis of publicly available data sets were performed on SMC and fibroblasts treated in the presence or absence of the MYC inhibitor JQ1. Validation of in silico findings were performed with qPCR, immunoblots, and collagen gel contraction assays measure the effect of JQ1 on cytoskeleton associated genes, proteins and contractility in mechanically active cells. Likelihood ratio test and FDR adjusted p-values were used to determine significant differentially expressed genes. Student ttest were used to calculate statistical significance of qPCR and contractility analyses.

RESULTS

Comparing PDGF and TGFβ stimulated SMC and fibroblasts identified a shared molecular profile regulated by MYC and members of the AP-1 transcription factor complex. Additional in silico analysis revealed a unique set of cytoskeleton-associated genes that were sensitive to MYC inhibition with JQ1. In vitro validation demonstrated JQ1 was also able to attenuate TGFβ and PDGF induced changes to the cytoskeleton and contraction of smooth muscle cells and fibroblasts in vitro.

CONCLUSIONS

These findings identify MYC as a key driver of aberrant cytoskeletal and contractile changes in fibroblasts and SMC, and suggest that JQ1 could be used to restore normal contractile function in hollow organs.

Investigation of the impact of bromodomain inhibition on cytoskeleton stability and contraction

Injury to contractile organs such as the heart, vasculature, urinary bladder and gut can stimulate a pathological response that results in loss of normal contractility. PDGF and TGFβ are among the most well studied initiators of the injury response and have been shown to induce aberrant contraction in mechanically active cells of hollow organs including smooth muscle cells (SMC) and fibroblasts. However the mechanisms driving contractile alterations downstream of PDGF and TGFβ in SMC and fibroblasts are incompletely understood, limiting therapeutic interventions. To identify potential molecular targets, we have leveraged the analysis of publicly available data, comparing transcriptomic changes in mechanically active cells stimulated with PDGF and TGFβ and identified a shared molecular profile regulated by MYC and members of the AP-1 transcription factor complex. We also analyzed data sets from SMC and fibroblasts treated in the presence or absence of the MYC inhibitor JQ1. This analysis revealed a unique set of cytoskeleton-associated genes that were sensitive to MYC inhibition. JQ1 was also able to attenuate TGFβ and PDGF induced changes to the cytoskeleton and contraction of smooth muscle cells and fibroblasts in vitro. These findings identify MYC as a key driver of aberrant cytoskeletal and contractile changes in fibroblasts and SMC, and suggest that JQ1 could be used to restore normal contractile function in hollow organs.

Unique Chirality Selection in Neural Cells for D-Matrix Enabling Specific Manipulation of Cell Behaviors

Manipulating neural cell behaviors is a critical issue to various therapies for neurological diseases and damages, where matrix chirality has long been overlooked despite the proven adhesion and proliferation improvement of multiple non-neural cells by L-matrixes. Here, it is reported that the D-matrix chirality specifically enhances cell density, viability, proliferation, and survival in four different types of neural cells, contrasting its inhibition in non-neural cells. This universal impact on neural cells is defined as "chirality selection for D-matrix" and is achieved through the activation of JNK and p38/MAPK signaling pathways by the cellular tension relaxation resulting from the weak interaction between D-matrix and cytoskeleton proteins, particularly actin. Also, D-matrix promotes sciatic nerve repair effectively, both with or without non-neural stem cell implantation, by improving the population, function, and myelination of autologous Schwann cells. D-matrix chirality, as a simple, safe, and effective microenvironment cue to specifically and universally manipulate neural cell behaviors, holds extensive application potential in addressing neurological issues such as nerve regeneration, neurodegenerative disease treatment, neural tumor targeting, and neurodevelopment.

Comparative- and network-based proteomic analysis of bacterial chondronecrosis with osteomyelitis lesions in broiler's proximal tibiae identifies new molecular signatures of lameness

Bacterial Chondronecrosis with Osteomyelitis (BCO) is a specific cause of lameness in commercial fast-growing broiler (meat-type) chickens and represents significant economic, health, and wellbeing burdens. However, the molecular mechanisms underlying the pathogenesis remain poorly understood. This study represents the first comprehensive characterization of the proximal tibia proteome from healthy and BCO chickens. Among a total of 547 proteins identified, 222 were differentially expressed (DE) with 158 up- and 64 down-regulated proteins in tibia of BCO vs. normal chickens. Biological function analysis using Ingenuity Pathways showed that the DE proteins were associated with a variety of diseases including cell death, organismal injury, skeletal and muscular disorder, immunological and inflammatory diseases. Canonical pathway and protein-protein interaction network analysis indicated that these DE proteins were involved in stress response, unfolded protein response, ribosomal protein dysfunction, and actin cytoskeleton signaling. Further, we identified proteins involved in bone resorption (osteoclast-stimulating factor 1, OSFT1) and bone structural integrity (collagen alpha-2 (I) chain, COL2A1), as potential key proteins involved in bone attrition. These results provide new insights by identifying key protein candidates involved in BCO and will have significant impact in understanding BCO pathogenesis.

Data driven and biophysical insights into the regulation of trafficking vesicles by extracellular matrix stiffness

Biomechanical signals from remodeled extracellular matrix (ECM) promote tumor progression. Here, we show that cell-matrix and cell-cell communication may be inherently linked and tuned through mechanisms of mechanosensitive biogenesis of trafficking vesicles. Pan-cancer analysis of cancer cells' mechanical properties (focusing primarily on cell stiffness) on substrates of varied stiffness and composition elucidated a heterogeneous cellular response to mechanical stimuli. Through machine learning, we identified a fingerprint of cytoskeleton-related proteins that accurately characterize cell stiffness in different ECM conditions. Expression of their respective genes correlates with patient prognosis across different tumor types. The levels of selected cytoskeleton proteins indicated that cortical tension mirrors the increase (or decrease) in cell stiffness with a change in ECM stiffness. A mechanistic biophysical model shows that the tendency for curvature generation by curvature-inducing proteins has an ultrasensitive dependence on cortical tension. This study thus highlights the effect of ECM stiffness, mediated by cortical tension, in modulating vesicle biogenesis.

Second-Generation JK-206 Targets the Oncogenic Signal Mediator RHOA in Gastric Cancer

Ras homologous A (RHOA), a signal mediator and a GTPase, is known to be associated with the progression of gastric cancer (GC), which is the fourth most common cause of death in the world. Previously, we designed pharmacologically optimized inhibitors against RHOA, including JK-136 and JK-139. Based on this previous work, we performed lead optimization and designed novel RHOA inhibitors for greater anti-GC potency. Two of these compounds, JK-206 and JK-312, could successfully inhibit the viability and migration of GC cell lines. Furthermore, using transcriptomic analysis of GC cells treated with JK-206, we revealed that the inhibition of RHOA might be associated with the inhibition of the mitogenic pathway. Therefore, JK-206 treatment for RHOA inhibition may be a new therapeutic strategy for regulating GC proliferation and migration.

High ARHGEF2 (GEF-H1) Expression is Associated with Poor Prognosis Via Cell Cycle Regulation in Patients with Pancreatic Cancer

BACKGROUND

Pancreatic cancer has an extremely poor prognosis, even after curative resection. Treatment options for pancreatic cancer remain limited, therefore new therapeutic targets are urgently needed. We searched for genes predictive of poor prognosis in pancreatic cancer using a public database and validated the survival impact of the selected gene in a patient cohort.

METHODS

We used a public database to search for genes associated with early pancreatic cancer recurrence. As a validation cohort, 201 patients who underwent radical resection in our institution were enrolled. Expression of the target gene was evaluated using immunohistochemistry (IHC). We evaluated growth and invasiveness using small interfering RNAs, then performed pathway analysis using gene set enrichment analysis.

RESULTS

We extracted ARHGEF2 from GSE21501 as a gene with a high hazard ratio (HR) for early recurrence within 1 year. The high ARHGEF2 expression group had significantly poorer recurrence-free survival (RFS) and poorer overall survival (OS) than the low ARHGEF2 expression group. Multivariate analysis demonstrated that high ARHGEF2 expression was an independent poor prognostic factor for RFS (HR 1.92) and OS (HR 1.63). In vitro, ARHGEF2 suppression resulted in reduced cell growth and invasiveness. Bioinformatic analysis revealed that ARHGEF2 expression was associated with MYC, G2M, E2F, and CDC25A expression, suggesting that c-Myc and cell cycle genes are associated with high ARHGEF2 expression. IHC revealed a positive correlation between ARHGEF2 and c-Myc expression.

CONCLUSIONS

High ARHGEF2 expression is associated with cell cycle progression, and predicts early recurrence and poor survival in patients with pancreatic cancer.

P21-Activated Kinase 1: Emerging biological functions and potential therapeutic targets in Cancer

The p21-Activated kinase 1 (PAK1), a member of serine-threonine kinases family, was initially identified as an interactor of the Rho GTPases RAC1 and CDC42, which affect a wide range of processes associated with cell motility, survival, metabolism, cell cycle, proliferation, transformation, stress, inflammation, and gene expression. Recently, the PAK1 has emerged as a potential therapeutic target in cancer due to its role in many oncogenic signaling pathways. Many PAK1 inhibitors have been developed as potential preclinical agents for cancer therapy. Here, we provide an overview of essential roles that PAK1 plays in cancer, including its structure and autoactivation mechanism, its crucial function from onset to progression to metastasis, metabolism, immune escape and even drug resistance in cancer; endogenous regulators; and cancer-related pathways. We also summarize the reported PAK1 small-molecule inhibitors based on their structure types and their potential application in cancer. In addition, we provide overviews on current progress and future challenges of PAK1 in cancer, hoping to provide new ideas for the diagnosis and treatment of cancer.

P120-Catenin And Its Phosphorylation On Tyr228 Inhibits Proliferation And Invasion In Colon Adenocarcinoma Cells

Background

Colorectal cancer is the third most common malignancy worldwide and is one of the leading causes of cancer-related mortality. P120-catenin protein has been well known to exert anticancer effects in several malignant diseases. The aim of our study was to investigate the phosphorylation of p120-catenin in colon adenocarcinoma (CAC) and its association with prognosis, and its role in tumor progression.

Methods

Immunohistochemical (IHC) staining was used to explore the existence of p120-catenin and its phosphorylation on tyrosine 228 (pY228-p120-catenin) in CAC samples. Overexpression and knockdown were achieved by transient transfection into SW480 cells using Lipofectamine 3000. CCK-8 and Matrigel-transwell assays were conducted to evaluate proliferation and invasion capacities, respectively. RT-qPCR and Western blotting were performed to analyze downstream signaling pathways. Chi-square test was used to analyze correlations between p120-catenin and clinicopathological characteristics. Univariate and multivariate analyses were used to identify independent prognostic factors.

Results

Lower p120-catenin and pY228-p120-catenin levels were identified in CAC tissues and were both correlated with advanced tumor stage. Additionally, lower pY228-p120-catenin indicated poorer prognosis of CAC patients although p120-catenin showed little significance. Overexpression of p120-catenin suppressed SW480 cell proliferation and invasion via stabilizing E-cadherin and inhibiting RhoA activation. Phosphorylation of Y228 on p120-catenin by Src protein enhanced the anticancer effects of p120-catenin.

Conclusion

P120-catenin and its phosphorylation on site Y228 play anticancer effects in colon adenocarcinoma via multiple signaling pathways. Hypophosphorylation of Y228 on p120-catenin in tumor tissues indicates poor clinical outcomes of colon adenocarcinoma patients.

ROCK and RHO Playlist for Preimplantation Development: Streaming to HIPPO Pathway and Apicobasal Polarity in the First Cell Differentiation

In placental mammalian development, the first cell differentiation produces two distinct lineages that emerge according to their position within the embryo: the trophectoderm (TE, placenta precursor) differentiates in the surface, while the inner cell mass (ICM, fetal body precursor) forms inside. Here, we discuss how such position-dependent lineage specifications are regulated by the RHOA subfamily of small GTPases and RHO-associated coiled-coil kinases (ROCK). Recent studies in mouse show that activities of RHO/ROCK are required to promote TE differentiation and to concomitantly suppress ICM formation. RHO/ROCK operate through the HIPPO signaling pathway, whose cell position-specific modulation is central to establishing unique gene expression profiles that confer cell fate. In particular, activities of RHO/ROCK are essential in outside cells to promote nuclear localization of transcriptional co-activators YAP/TAZ, the downstream effectors of HIPPO signaling. Nuclear localization of YAP/TAZ depends on the formation of apicobasal polarity in outside cells, which requires activities of RHO/ROCK. We propose models of how RHO/ROCK regulate lineage specification and lay out challenges for future investigations to deepen our understanding of the roles of RHO/ROCK in preimplantation development. Finally, as RHO/ROCK may be inhibited by certain pharmacological agents, we discuss their potential impact on human preimplantation development in relation to fertility preservation in women.

RhoA regulates Schwann cell differentiation through JNK pathway

RhoA is a small GTPase that regulates many functions of mammalian cells via actin reorganization. Lots of studies uncovered that its activation acts as a major negative regulator of neurite extension, and inhibition of RhoA activity or reduction of its expression can promote neuron survival and axonal regeneration. However, little is known about whether RhoA also exerts important functions on Schwann cells (SCs) which are the glial cells of the peripheral nervous system (PNS). Recently, we reported that RhoA plays important roles in the proliferation, migration and myelination of SCs. In the present study, using RNA interference to knockdown RhoA expression and CT04 (a cell-permeable C3 Transferase) to inhibit RhoA activation we found that blocking RhoA can slack SC differentiation. Unexpectedly, inhibiting ROCK, the mostly well-known downstream effector of RhoA, has no influence on SC differentiation. Instead, the inhibition of RhoA in differentiating SCs results in the activation of JNK and p38 MAPK. And the inhibitor of JNK but not p38 MAPK can promote SC differentiation in the presence of RhoA inhibition. Overall results indicate that RhoA plays a vital role in SC differentiation via JNK pathway rather than ROCK pathway.

MYC leads the way

Members of the MYC family of proto-oncogenes are the most commonly deregulated genes in all human cancers. MYC proteins drive an increase in cellular proliferation and facilitate multiple aspects of tumor initiation and progression, thereby controlling all hallmarks of cancer. MYC's ability to drive metabolic reprogramming of tumor cells leading to biomass accumulation and cellular proliferation is the most studied function of these oncogenes. MYC also regulates tumor progression and is often implicated in resistance to chemotherapy and in metastasis. While most oncogenic functions of MYC are attributed to its role as a transcription factor, more recently, new roles of MYC as a pro-survival factor in the cytoplasm suggest a previously unappreciated diversity in MYC's roles in cancer progression. This review will focus on the role of MYC in invasion and will discuss the canonical functions of MYC in Epithelial to Mesenchymal Transition and the cytoplasmic functions of MYC-nick in collective migration.

Pathway analysis in attention deficit hyperactivity disorder: An ensemble approach

Despite a wealth of evidence for the role of genetics in attention deficit hyperactivity disorder (ADHD), specific and definitive genetic mechanisms have not been identified. Pathway analyses, a subset of gene-set analyses, extend the knowledge gained from genome-wide association studies (GWAS) by providing functional context for genetic associations. However, there are numerous methods for association testing of gene sets and no real consensus regarding the best approach. The present study applied six pathway analysis methods to identify pathways associated with ADHD in two GWAS datasets from the Psychiatric Genomics Consortium. Methods that utilize genotypes to model pathway-level effects identified more replicable pathway associations than methods using summary statistics. In addition, pathways implicated by more than one method were significantly more likely to replicate. A number of brain-relevant pathways, such as RhoA signaling, glycosaminoglycan biosynthesis, fibroblast growth factor receptor activity, and pathways containing potassium channel genes, were nominally significant by multiple methods in both datasets. These results support previous hypotheses about the role of regulation of neurotransmitter release, neurite outgrowth and axon guidance in contributing to the ADHD phenotype and suggest the value of cross-method convergence in evaluating pathway analysis results. © 2016 Wiley Periodicals, Inc.

PIWIL2 induces c-Myc expression by interacting with NME2 and regulates c-Myc-mediated tumor cell proliferation

c-Myc serves as a crucial regulator in multiple cellular events. Cumulative evidences demonstrate that anomalous c-Myc overexpression correlates with proliferation, invasion and metastasis in various human tumors. However, the transcriptionally activating mechanisms responsible for c-Myc overexpression are complex and continue to be intangible. Here we showed that Piwi-Like RNA-Mediated Gene Silencing 2 (PIWIL2) can upregulate c-Myc via binding with NME/NM23 nucleoside diphosphate kinase 2 (NME2). PIWIL2 promotes c-Myc transcription by interacting with and facilitating NME2 to bind to G4-motif region within c-Myc promoter. Interestingly, in a c-Myc-mediated manner, PIWIL2 upregulates RhoA, which in turn induces filamentary F-actin. Deficiency of PIWIL2 results in obstacle for c-Myc expression, cell cycle progress and cell proliferation. Taken together, our present work demonstrates that PIWIL2 modulates tumor cell proliferation and F-actin filaments via promoting c-Myc expression.

A transcriptional cross-talk between RhoA and c-Myc inhibits the RhoA/Rock-dependent cytoskeleton

The GTPase RhoA and the transcriptional factor c-Myc are closely intertwined in cancer cells. Although this cross-talk results in potent synergistic effects that favor the transformed phenotype of cancer cells, recent results from our laboratory indicate that c-Myc also participates in a negative feed-back loop that blocks specific RhoA signaling branches connected to the induction of stress fibers, focal adhesions and actomyosin contractility. Using microarray analysis, we have unveiled a RhoA/c-Myc-dependent gene signature in charge of this negative cross-talk. This signature is composed of upregulated and repressed transcripts encoding cytoskeletal modulators located downstream of both RhoA and Rock. Our results also indicate that this negative feed-back loop modifies the invasion and adhesion properties of RhoA-transformed cells, suggesting that it may be important to ensure fluid cytoskeletal dynamics of cancer cells. Preliminary data indicate that c-Myc may also use a different transcriptional program to interfere with the RhoA/Rock-dependent cytoskeletal branch in non-transformed cells.

Thrombospondin-1 repression is mediated via distinct mechanisms in fibroblasts and epithelial cells

Tumor-associated angiogenesis is postulated to be regulated by the balance between pro- and anti-angiogenic factors. We demonstrate here that the critical step in establishing the angiogenic capability of human tumor cells is the repression of a key secreted anti-angiogenic factor, thrombospondin-1 (Tsp-1). This repression is essential for tumor formation by mammary epithelial cells and kidney cells engineered to express SV40 early region proteins, hTERT, and H-RasV12. In transformed epithelial cells, a signaling pathway leading from Ras to Tsp-1 repression induces the sequential activation of PI3 kinase, Rho and ROCK, leading to activation of Myc through phosphorylation, thereby enabling Myc to repress Tsp-1 transcription. In transformed fibroblasts, however, the repression of Tsp-1 can be achieved by an alternative mechanism involving inactivation of both p53 and pRb. We thus describe novel mechanisms by which the activation of oncogenes in epithelial cells and the inactivation of tumor suppressors in fibroblasts permits angiogenesis and, in turn, tumor formation.

B7-H1, which represses EBV-immortalized B cell killing by autologous T and NK cells, is oppositely regulated by c-Myc and EBV latency III program at both mRNA and secretory lysosome levels

EBV-immortalized B cells induce a complex immune response such that the virus persists as a clinically silent infection for the lifetime of the infected host. B7-H1, also called PD-L1, is a cosignaling molecule of the B7 family that can inhibit activated T cell effectors by interaction with its receptor PD-1. In this work, we have studied the dependence of B7-H1 on NF-κB and c-Myc, the two main transcription factors in EBV latency III proliferating B cells, on various lymphoblastoid and Burkitt lymphoma cell lines, some of them being inducible or not for the EBV latency III program and/or for c-Myc. We found that B7-H1 repressed killing of EBV-immortalized B cells by their autologous T and NK cells. At the mRNA level, NF-κB was a weak inducer whereas c-Myc was a strong repressor of B7-H1 expression, an effect mediated by STAT1 inhibition. At the protein level, B7-H1 molecules were stored in both degradative and unconventional secretory lysosomes. Surface membrane B7-H1 molecules were constitutively internalized and proteolyzed in lysosomes. The EBV latency III program increased the amounts of B7-H1-containing secretory lysosomes and their export to the surface membrane. By repressing actin polymerization, c-Myc blocked secretory lysosome migration and B7-H1 surface membrane export. In addition to B7-H1, various immunoregulatory molecules participating in the immunological synapse are stored in secretory lysosomes. By playing on actin polymerization, c-Myc could thus globally regulate the immunogenicity of transformed B cells, acting on export of secretory lysosomes to plasma membrane.

MicroRNA-34a suppresses malignant transformation by targeting c-Myc transcriptional complexes in human renal cell carcinoma

We investigated the functional effects of microRNA-34a (miR-34a) on c-Myc transcriptional complexes in renal cell carcinoma. miR-34a down-regulated expression of multiple oncogenes including c-Myc by targeting its 3' untranslated region, which was revealed by luciferase reporter assays. miR-34a was also found to repress RhoA expression by suppressing the c-Myc-Skp2-Miz1 transcriptional complex that activates RhoA. Overexpression of c-Myc reversed miR-34a suppression of RhoA expression and inhibition of cell invasion, suggesting that miR-34a inhibits invasion by suppressing RhoA through c-Myc. miR-34a was also found to repress the c-Myc-P-TEFb transcription elongation complex, indicating one of the mechanisms by which miR-34a has profound effects on cellular functions. Our results demonstrate that miR-34a suppresses assembly and function of the c-Myc complex that activates or elongates transcription, indicating a novel role of miR-34a in the regulation of transcription by c-Myc.

Immunohistochemical expression of Rho GTPases in ameloblastomas

Rho GTPases are proteins that regulate cell cycle, shape, polarization, invasion, migration, and apoptosis, which are important characteristics of normal and neoplastic cells. Rho GTPases expression has been reported in normal tooth germ and several pathologies; however, it has not been evaluated in ameloblastomas. The aim of this study was to analyze the expression and distribution of RhoA, RhoB, Rac1, and Cdc42 Rho GTPases in solid and unicystic ameloblastomas. Three-micrometer sections from paraffin-embedded specimens were evaluated by using an avidin-biotin immunohistochemical method with antibodies against the proteins mentioned above. RhoA and RhoB staining was observed in a high number of cells (P < 0.05) and greater intensity in non-polarized ones. Rac1 was not observed, and Cdc42 did not show any statistical differences between the number of non-polarized and basal positive cells (P > 0.05). Upon comparing the studied ameloblastomas, a higher number of positive cells in the unicystic variant was observed than that in the solid one (P < 0,05). The results obtained suggest that these GTPases could play a role in the ameloblastoma neoplastic epithelial cell phenotype determination (polarized or non-polarized), as well as in variant (solid or unicystic) and subtype (follicular or plexiform) determination. Furthermore, they could participate in solid ameloblastoma invasion mechanisms.