RSK2 drives cell motility by serine phosphorylation of LARG and activation of Rho GTPases

RSK/GSK3-mediated phosphorylation of FilGAP regulates chemotactic cancer invasion

Cell migration plays a crucial role in various biological processes, such as gastrulation, immune response, and cancer metastasis. In response to chemoattractant-like growth factors, cells form protrusions and migrate toward the source of the signal. Rho family small GTPase Rac is a key regulator of cell migration by stimulating actin polymerization to generate lamellipodia, flat membrane protrusions at the leading edge of migrating cells. FilGAP (ARHGAP24), a Rac-specific GTPase-activating protein (GAP), suppresses lamellipodia formation, and controls tumor cell migration. In this study, we found that FilGAP is phosphorylated downstream of epidermal growth factor (EGF) signaling. Upon EGF stimulation, FilGAP is phosphorylated at Ser625 by p90 ribosomal S6 kinase (RSK) and then at Ser621 by glycogen synthase kinase 3 (GSK3). Phosphorylation of FilGAP induces its dissociation from actin filaments. We identified a novel actin-localization domain of FilGAP that is essential for stabilizing cell adhesion. Additionally, we found that phosphorylation of FilGAP inhibits its lamellipodia suppression activity. Finally, we showed the expression of nonphosphorylatable FilGAP mutant, but not wild-type FilGAP, reduced cell migration speed and persistence toward the EGF gradient. Taken together, our results suggest that phosphorylation of FilGAP downstream of EGF-signaling plays a critical role in regulating chemotactic tumor cell migration by controlling cell-matrix adhesion and protrusion formation.

ROK and RSK2-kinase pathways differ between senescent human renal and mesenteric arteries

OBJECTIVE

Small arteries from different organs vary with regard to the mechanisms that regulate vasoconstriction. This study investigated the impact of advanced age on the regulation of vasoconstriction in isolated human small arteries from kidney cortex and periintestinal mesenteric tissue.

METHODS

Renal and mesenteric tissues were obtained from patients (mean age 71 ± 9 years) undergoing elective surgery. Furthermore, intrarenal and mesenteric arteries from young and aged mice were studied. Arteries were investigated by small vessel myography and western blot.

RESULTS

Human intrarenal arteries (h-RA) showed higher stretch-induced tone and higher reactivity to α 1 adrenergic receptor stimulation than human mesenteric arteries (h-MA). Rho-kinase (ROK) inhibition resulted in a greater decrease in Ca 2+ and depolarization-induced tone in h-RA than in h-MA. Basal and α 1 adrenergic receptor stimulation-induced phosphorylation of the regulatory light chain of myosin (MLC 20 ) was higher in h-RA than in h-MA. This was associated with higher ROK-dependent phosphorylation of the regulatory subunit of myosin light-chain-phosphatase (MLCP), MYPT1-T853. In h-RA phosphorylation of ribosomal S6-kinase II (RSK2-S227) was significantly higher than in h-MA. Stretch-induced tone and RSK2 phosphorylation was also higher in interlobar arteries (m-IAs) from aged mice than in respective vessels from young mice and in murine mesenteric arteries (m-MA) from both age groups.

CONCLUSION

Vasoconstriction in human intrarenal arteries shows a greater ROK-dependence than in mesenteric arteries. Activation of RSK2 may contribute to intrarenal artery tone dysregulation associated with aging. Compared with h-RA, h-MA undergo age-related remodeling leading to a reduction of the contractile response to α 1 adrenergic stimulation.

Dual thick and thin filament linked regulation of stretch- and L-NAME-induced tone in young and senescent murine basilar artery

Stretch-induced vascular tone is an important element of autoregulatory adaptation of cerebral vasculature to maintain cerebral flow constant despite changes in perfusion pressure. Little is known as to the regulation of tone in senescent basilar arteries. We tested the hypothesis, that thin filament mechanisms in addition to smooth muscle myosin-II regulatory-light-chain-(MLC20)-phosphorylation and non-muscle-myosin-II, contribute to regulation of stretch-induced tone. In young BAs (y-BAs) mechanical stretch does not lead to spontaneous tone generation. Stretch-induced tone in y-BAs appeared only after inhibition of NO-release by L-NAME and was fully prevented by treatment with 3 μmol/L RhoA-kinase (ROK) inhibitor Y27632. L-NAME-induced tone was reduced in y-BAs from heterozygous mice carrying a point mutation of the targeting-subunit of the myosin phosphatase, MYPT1 at threonine696 (MYPT1-T696A/+). In y-BAs, MYPT1-T696A-mutation also blunted the ability of L-NAME to increase MLC20-phosphorylation. In contrast, senescent BAs (s-BAs; >24 months) developed stable spontaneous stretch-induced tone and pharmacological inhibition of NO-release by L-NAME led to an additive effect. In s-BAs the MYPT1-T696A mutation also blunted MLC20-phosphorylation, but did not prevent development of stretch-induced tone. In s-BAs from both lines, Y27632 completely abolished stretch- and L-NAME-induced tone. In s-BAs phosphorylation of non-muscle-myosin-S1943 and PAK1-T423, shown to be down-stream effectors of ROK was also reduced by Y27632 treatment. Stretch- and L-NAME tone were inhibited by inhibition of non-muscle myosin (NM-myosin) by blebbistatin. We also tested whether the substrate of PAK1 the thin-filament associated protein, caldesmon is involved in the regulation of stretch-induced tone in advanced age. BAs obtained from heterozygotes Cald1+/− mice generated stretch-induced tone already at an age of 20–21 months old BAs (o-BA). The magnitude of stretch-induced tone in Cald1+/− o-BAs was similar to that in s-BA. In addition, truncation of caldesmon myosin binding Exon2 (CaD-▵Ex2−/−) did not accelerate stretch-induced tone. Our study indicates that in senescent cerebral vessels, mechanisms distinct from MLC20 phosphorylation contribute to regulation of tone in the absence of a contractile agonist. While in y-and o-BA the canonical pathways, i.e., inhibition of MLCP by ROK and increase in pMLC20, predominate, tone regulation in senescence involves ROK regulated mechanisms, involving non-muscle-myosin and thin filament linked mechanisms involving caldesmon.

RSK inhibitors as potential anticancer agents: Discovery, optimization, and challenges

Ribosomal S6 kinase (RSK) family is a group of serine/threonine kinases, including four isoforms (RSK1/2/3/4). As a downstream effector of the Ras-mitogen-activated protein kinase (Ras-MAPK) pathway, RSK participates in many physiological activities such as cell growth, proliferation, and migration, and is intimately involved in tumor occurrence and development. As a result, it is recognized as a potential target for anti-cancer and anti-resistance therapies. There have been several RSK inhibitors discovered or designed in recent decades, but only two have entered clinical trials. Low specificity, low selectivity, and poor pharmacokinetic properties in vivo limit their clinical translation. Published studies performed structure optimization by increasing interaction with RSK, avoiding hydrolysis of pharmacophores, eliminating chirality, adapting to binding site shape, and becoming prodrugs. Besides enhancing efficacy, the focus of further design will move towards selectivity since there are functional differences among RSK isoforms. This review summarized the types of cancers associated with RSK, along with the structural characteristics and optimization process of the reported RSK inhibitors. Furthermore, we addressed the importance of RSK inhibitors' selectivity and discussed future drug development directions. This review is expected to shed light on the emergence of RSK inhibitors with high potency, specificity, and selectivity.

Targeting ARHGEF12 promotes neuroblastoma differentiation, MYCN degradation, and reduces tumorigenicity

PURPOSE

Neuroblastoma arises from developmental block of embryonic neural crest cells and is one of the most common and deadly pediatric tumors. However, the mechanism underlying this block is still unclear. Here, we show that targeting Rho guanine nucleotide exchange factor 12 (ARHGEF12, also named LARG) promotes MYCN degradation and neuroblastoma differentiation, leading to reduced neuroblastoma malignancy.

METHODS

The neuroblastoma TARGET dataset was downloaded to assess ARHGEF12 expression. Cell differentiation, proliferation, colony formation and cell migration analyses were performed to investigate the effects of ARHGEF12 knockdown on neuroblastoma cells. Western blotting and immunohistochemistry were employed to determine protein expression. Animal xenograft models were used to investigate antitumor effects after ARHGEF12 knockdown or treatment with the ARHGEF12 inhibitor Y16 in vivo.

RESULTS

We found that the expression level of ARHGEF12 was higher in neuroblastoma than in better-differentiated ganglioneuroblastoma. Knockdown of ARHGEF12 promoted neuroblastoma differentiation, decreased stemness-related gene expression, and increased differentiation-related gene expression. ARHGEF12 knockdown reduced tumor growth, and the resulting tumors showed bigger tumor cells compared to those in control neuroblastoma xenografts. In addition, it was found that ARHGEF12 knockdown promoted MYCN ubiquitination and degradation in MYCN-amplified tumors through RhoA/ROCK/GSK3β signaling. Targeting ARHGEF12 with the small molecular inhibitor Y16 induced cell differentiation and attenuated neuroblastoma tumorigenicity.

CONCLUSION

Our findings provide new insight into the mechanism by which ARHGEF12 regulates neuroblastoma tumorigenicity and suggest a translatable therapeutic approach by targeting ARHGEF12 with a small molecular inhibitor.

RSK1 and RSK2 serine/threonine kinases regulate different transcription programs in cancer

The 90 kDa ribosomal S6 kinases (RSKs) are serine threonine kinases comprising four isoforms. The isoforms can have overlapping functions in regulation of migration, invasion, proliferation, survival, and transcription in various cancer types. However, isoform specific differences in RSK1 versus RSK2 functions in gene regulation are not yet defined. Here, we delineate ribosomal S6 kinases isoform-specific transcriptional gene regulation by comparing transcription programs in RSK1 and RSK2 knockout cells using microarray analysis. Microarray analysis revealed significantly different mRNA expression patterns between RSK1 knockout and RSK2 knockout cell lines. Importantly some of these functions have not been previously recognized. Our analysis revealed RSK1 has specific roles in cell adhesion, cell cycle regulation and DNA replication and repair pathways, while RSK2 has specific roles in the immune response and interferon signaling pathways. We further validated that the identified gene sets significantly correlated with mRNA datasets from cancer patients. We examined the functional significance of the identified transcriptional programs using cell assays. In alignment with the microarray analysis, we found that RSK1 modulates the mRNA and protein expression of Fibronectin1, affecting cell adhesion and CDK2, affecting S-phase arrest in the cell cycle, and impairing DNA replication and repair. Under similar conditions, RSK2 showed increased ISG15 transcriptional expression, affecting the immune response pathway and cytokine expression. Collectively, our findings revealed the occurrence of RSK1 and RSK2 specific transcriptional regulation, defining separate functions of these closely related isoforms.

The role of RAS oncogenes in controlling epithelial mechanics

Mutations in RAS are key oncogenic drivers and therapeutic targets. Oncogenic Ras proteins activate a network of downstream signalling pathways, including extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase (PI3K), promoting cell proliferation and survival. However, there is increasing evidence that RAS oncogenes also alter the mechanical properties of both individual malignant cells and transformed tissues. Here we discuss the role of oncogenic RAS in controlling mechanical cell phenotypes and how these mechanical changes promote oncogenic transformation in single cells and tissues. RAS activation alters actin organisation and actomyosin contractility. These changes alter cell rheology and impact mechanosensing through changes in substrate adhesion and YAP/TAZ-dependent mechanotransduction. We then discuss how these changes play out in cell collectives and epithelial tissues by driving large-scale tissue deformations and the expansion of malignant cells. Uncovering how RAS oncogenes alter cell mechanics will lead to a better understanding of the morphogenetic processes that underlie tumour formation in RAS-mutant cancers.

MLL regulates the actin cytoskeleton and cell migration by stabilising Rho GTPases via the expression of RhoGDI1

Attainment of proper cell shape and the regulation of cell migration are essential processes in the development of an organism. The mixed lineage leukemia (MLL or KMT2A) protein, a histone 3 lysine 4 (H3K4) methyltransferase, plays a critical role in cell-fate decisions during skeletal development and haematopoiesis in higher vertebrates. Rho GTPases - RhoA, Rac1 and CDC42 - are small G proteins that regulate various key cellular processes, such as actin cytoskeleton formation, the maintenance of cell shape and cell migration. Here, we report that MLL regulates the homeostasis of these small Rho GTPases. Loss of MLL resulted in an abnormal cell shape and a disrupted actin cytoskeleton, which lead to diminished cell spreading and migration. MLL depletion affected the stability and activity of Rho GTPases in a SET domain-dependent manner, but these Rho GTPases were not direct transcriptional targets of MLL. Instead, MLL regulated the transcript levels of their chaperone protein RhoGDI1 (also known as ARHGDIA). Using MDA-MB-231, a triple-negative breast cancer cell line with high RhoGDI1 expression, we show that MLL depletion or inhibition by small molecules reduces tumour progression in nude mice. Our studies highlight the central regulatory role of MLL in Rho/Rac/CDC42 signalling pathways. This article has an associated First Person interview with the first author of the paper.

ERK2 signaling regulates cell-cell adhesion of epithelial cells and enhances growth factor-induced cell scattering

The ERK signaling pathway, consisting of core protein kinases Raf, MEK and effector kinases ERK1/2, regulates various biological outcomes such as cell proliferation, differentiation, apoptosis, or cell migration. Signal transduction through the ERK signaling pathway is tightly controlled at all levels of the pathway. However, it is not well understood whether ERK pathway signaling can be modulated by the abundance of ERK pathway core kinases. In this study, we investigated the effects of low-level overexpression of the ERK2 isoform on the phenotype and scattering of cuboidal MDCK epithelial cells growing in discrete multicellular clusters. We show that ERK2 overexpression reduced the vertical size of lateral membranes that contain cell-cell adhesion complexes. Consequently, ERK2 overexpressing cells were unable to develop cuboidal shape, remained flat with increased spread area and intercellular adhesive contacts were present only on the basal side. Interestingly, ERK2 overexpression was not sufficient to increase phosphorylation of multiple downstream targets including transcription factors and induce global changes in gene expression, namely to increase the expression of pro-migratory transcription factor Fra1. However, ERK2 overexpression enhanced HGF/SF-induced cell scattering as these cells scattered more rapidly and to a greater extent than parental cells. Our results suggest that an increase in ERK2 expression primarily reduces cell-cell cohesion and that weakened intercellular adhesion synergizes with upstream signaling in the conversion of the multicellular epithelium into single migrating cells. This mechanism may be clinically relevant as the analysis of clinical data revealed that in one type of cancer, pancreatic adenocarcinoma, ERK2 overexpression correlates with a worse prognosis.

The putative oncogenic role of WDTC1 in colorectal cancer

Microsatellite instability (MSI) is detected in approximately 15% of colorectal cancers (CRCs). WD40 and tetratricopeptide repeats 1 (WDTC1) is frequently mutated in MSI CRC, indicating that it may contribute to CRC development. However, the functional evidence of the role of WDTC1 in CRC development remains unknown. Herein, we conducted in vitro assays to examine the function of WDTC1 using knockdown experiments in three CRC cell lines, SW480, CACO2, and LoVo. We provided strong evidence that silencing WDTC1 significantly suppressed cell proliferation, migration, and invasion consistently in all three CRC cell lines. To evaluate the potential role of WDTC1 in regulating CRC-related genes, we conducted RNA sequencing after 24 and 48 h in SW480 cells after treating WDTC1-siRNA and its vehicle control cells. Differential gene expression analysis identified 44 (42 downregulated and 2 upregulated) and 16 (all downregulated) genes, at time points of 24 and 48 h, respectively, whereas 15 downregulated genes were commonly detected at both time points. The ingenuity pathways analysis suggested that the most significant enrichments associated with cancer function and upstream regulator ATM/ATR were observed for these commonly observed genes. We further verified differential gene expression of eight cancer-related genes, ARHGEF12, GSTP1, FNDC3A, TMTC3, RTN4, RRM2, UHMK1, and PTPRF, using RT-PCR in all three cell lines. Our findings provided additional insight into the oncogenic role of WDTC1 in CRC development.

Thiazole and Related Heterocyclic Systems as Anticancer Agents: A Review on Synthetic Strategies, Mechanisms of Action and SAR Studies

Background:

Cancer is the second leading cause of death throughout the world. Many anticancer drugs are commercially available, but lack of selectivity, target specificity, cytotoxicity and development of resistance lead to serious side effects. There have been several experiments going on to develop compounds with minor or no side effects.

Objective:

This review mainly emphasizes synthetic strategies, SAR studies, and mechanism of action for thiazole, benzothiazole, and imidazothiazole containing compounds as anticancer agents.

Methods:

Recent literature related to thiazole and thiazole-related derivatives endowed with encouraging anticancer potential is reviewed. This review emphasizes contemporary strategies used for the synthesis of thiazole and related derivatives, mechanistic targets, and comprehensive structural activity relationship studies to provide perspective into the rational design of high-efficiency thiazole-based anticancer drug candidates.

Results:

Exhaustive literature survey indicated that thiazole derivatives are associated with properties of inducing apoptosis and disturbing tubulin assembly. Thiazoles are also associated with the inhibition of NFkB/mTOR/PI3K/AkT and regulation of estrogen-mediated activity. Furthermore, thiazole derivatives have been found to modulate critical targets such as topoisomerase and HDAC.

Conclusion:

Thiazole derivatives seem to be quite competent and act through various mechanisms. Some of the thiazole derivatives, such as compounds 29, 40, 62, and 74a with IC50 values of 0.05 μM, 0.00042 μM, 0.18 μM, and 0.67 μM, respectively not only have anticancer activity but they also have lower toxicity and better absorption. Therefore, some other similar compounds could be investigated to aid in the development of anticancer pharmacophores.

Regulation of Leukaemia Associated Rho GEF (LARG/ARHGEF12)

The Ras homologous (Rho) protein family of GTPases (RhoA, RhoB and RhoC) are the members of the Ras superfamily and regulate cellular processes such as cell migration, proliferation, polarization, adhesion, gene transcription and cytoskeletal structure. Rho GTPases function as molecular switches that cycle between GTP-bound (active state) and GDP-bound (inactive state) forms. Leukaemia-associated RhoGEF (LARG) is a guanine nucleotide exchange factor (GEF) that activates RhoA subfamily GTPases by promoting the exchange of GDP for GTP. LARG is selective for RhoA subfamily GTPases and is an essential regulator of cell migration and invasion. Here, we describe the mechanisms by which LARG is regulated to facilitate the understanding of how LARG mediates functions like cell motility and to provide insight for better therapeutic targeting of these functions.

Matriptase activation of Gq drives epithelial disruption and inflammation via RSK and DUOX

Epithelial tissues are primed to respond to insults by activating epithelial cell motility and rapid inflammation. Such responses are also elicited upon overexpression of the membrane-bound protease, Matriptase, or mutation of its inhibitor, Hai1. Unrestricted Matriptase activity also predisposes to carcinoma. How Matriptase leads to these cellular outcomes is unknown. We demonstrate that zebrafish hai1a mutants show increased H₂O₂, NfκB signalling, and IP₃R -mediated calcium flashes, and that these promote inflammation, but do not generate epithelial cell motility. In contrast, inhibition of the Gq subunit in hai1a mutants rescues both the inflammation and epithelial phenotypes, with the latter recapitulated by the DAG analogue, PMA. We demonstrate that hai1a has elevated MAPK pathway activity, inhibition of which rescues the epidermal defects. Finally, we identify RSK kinases as MAPK targets disrupting adherens junctions in hai1a mutants. Our work maps novel signalling cascades mediating the potent effects of Matriptase on epithelia, with implications for tissue damage response and carcinoma progression.

Cancer occurs when normal processes in the cell become corrupted or unregulated. Many proteins can contribute, including one enzyme called Matriptase that cuts other proteins at specific sites. Matriptase activity is tightly controlled by a protein called Hai1. In mice and zebrafish, when Hai1 cannot adequately control Matriptase activity, invasive cancers with severe inflammation develop. However, it is unclear how unregulated Matriptase leads to both inflammation and cancer invasion.

One outcome of Matriptase activity is removal of proteins called Cadherins from the cell surface. These proteins have a role in cell adhesion: they act like glue to stick cells together. Without them, cells can dissociate from a tissue and move away, a critical step in cancer cells invading other organs. However, it is unknown exactly how Matriptase triggers the removal of Cadherins from the cell surface to promote invasion.

Previous work has shown that Matriptase switches on a receptor called Proteinase-activated receptor 2, or Par2 for short, which is known to activate many enzymes, including one called phospholipase C. When activated, this enzyme releases two signals into the cell: a sugar called inositol triphosphate, IP3; and a lipid or fat called diacylglycerol, DAG. It is possible that these two signals have a role to play in how Matriptase removes Cadherins from the cell surface.

To find out, Ma et al. mapped the effects of Matriptase in zebrafish lacking the Hai1 protein. This revealed that Matriptase increases IP3 and DAG levels, which initiate both inflammation and invasion. IP3 promotes inflammation by switching on pro-inflammatory signals inside the cell such as the chemical hydrogen peroxide. At the same time, DAG promotes cell invasion by activating a well-known cancer signalling pathway called MAPK. This pathway activates a protein called RSK. Ma et al. show that this protein is required to remove Cadherins from the surface of cells, thus connecting Matriptase’s activation of phospholipase C with its role in disrupting cell adhesion.

An increase in the ratio of Matriptase to HAI-1 (the human equivalent of Hai1) is present in many cancers. For this reason, the signal cascades described by Ma et al. may be of interest in developing treatments for these cancers. Understanding how these signals work together could lead to more direct targeted anti-cancer approaches in the future.

The role of the p90 ribosomal S6 kinase family in prostate cancer progression and therapy resistance

Prostate cancer (PCa) is the second most commonly occurring cancer in men, with over a million new cases every year worldwide. Tumor growth and disease progression is mainly dependent on the Androgen Receptor (AR), a ligand dependent transcription factor. Standard PCa therapeutic treatments include androgen-deprivation therapy and AR signaling inhibitors. Despite being successful in controlling the disease in the majority of men, the high frequency of disease progression to aggressive and therapy resistant stages (termed castrate resistant prostate cancer) has led to the search for new therapeutic targets. The p90 ribosomal S6 kinase (RSK1-4) family is a group of highly conserved Ser/Thr kinases that holds promise as a novel target. RSKs are effector kinases that lay downstream of the Ras/Raf/MEK/ERK signaling pathway, and aberrant activation or expression of RSKs has been reported in several malignancies, including PCa. Despite their structural similarities, RSK isoforms have been shown to perform nonredundant functions and target a wide range of substrates involved in regulation of transcription and translation. In this article we review the roles of the RSKs in proliferation and motility, cell cycle control and therapy resistance in PCa, highlighting the possible interplay between RSKs and AR in mediating disease progression. In addition, we summarize the current advances in RSK inhibitor development and discuss their potential clinical benefits.

Dynamic Control of Signaling by Phosphorylation of PDZ Binding Motifs

The dynamic regulation of protein-protein interactions (PPIs) involves phosphorylation of short liner motifs in disordered protein regions modulating binding affinities. The ribosomal-S6-kinase 1 is capable of binding to scaffold proteins containing PDZ domains through a PDZ-binding motif (PBM) located at the disordered C-terminus of the kinase. Phosphorylation of the PBM dramatically changes the interactome of RSK1 with PDZ domains exerting a fine-tuning mechanism to regulate PPIs. Here we present in detail highly effective biophysical (fluorescence polarization, isothermal calorimetry) and cellular (protein-fragment complementation) methods to study the effect of phosphorylation on RSK1-PDZ interactions that can be also applied to investigate phosphoregulation of other PPIs in signaling pathways.

Leukemia-Associated Rho Guanine Nucleotide Exchange Factor and Ras Homolog Family Member C Play a Role in Glioblastoma Cell Invasion and Resistance

Glioblastoma (GBM) is the most common primary malignant brain cancer in adults. A hallmark of GBM is aggressive invasion of tumor cells into the surrounding normal brain. Both the current standard of care and targeted therapies have largely failed to specifically address this issue. Therefore, identifying key regulators of GBM cell migration and invasion is important. The leukemia-associated Rho guanine nucleotide exchange factor (LARG) has previously been implicated in cell invasion in other tumor types; however, its role in GBM pathobiology remains undefined. Herein, we report that the expression levels of LARG and ras homolog family members C (RhoC), and A (RhoA) increase with glial tumor grade and are highest in GBM. LARG and RhoC protein expression is more prominent in invading cells, whereas RhoA expression is largely restricted to cells in the tumor core. Knockdown of LARG by siRNA inhibits GBM cell migration in vitro and invasion ex vivo in organotypic brain slices. Moreover, siRNA-mediated silencing of RhoC suppresses GBM cell migration in vitro and invasion ex vivo, whereas depletion of RhoA enhances GBM cell migration and invasion, supporting a role for LARG and RhoC in GBM cell migration and invasion. Depletion of LARG increases the sensitivity of GBM cells to temozolomide treatment. Collectively, these results suggest that LARG and RhoC may represent unappreciated targets to inhibit glioma invasion.

ERK signalling: a master regulator of cell behaviour, life and fate

The proteins extracellular signal-regulated kinase 1 (ERK1) and ERK2 are the downstream components of a phosphorelay pathway that conveys growth and mitogenic signals largely channelled by the small RAS GTPases. By phosphorylating widely diverse substrates, ERK proteins govern a variety of evolutionarily conserved cellular processes in metazoans, the dysregulation of which contributes to the cause of distinct human diseases. The mechanisms underlying the regulation of ERK1 and ERK2, their mode of action and their impact on the development and homeostasis of various organisms have been the focus of much attention for nearly three decades. In this Review, we discuss the current understanding of this important class of kinases. We begin with a brief overview of the structure, regulation, substrate recognition and subcellular localization of ERK1 and ERK2. We then systematically discuss how ERK signalling regulates six fundamental cellular processes in response to extracellular cues. These processes are cell proliferation, cell survival, cell growth, cell metabolism, cell migration and cell differentiation.

Logic-based analysis of gene expression data predicts association between TNF, TGFB1 and EGF pathways in basal-like breast cancer

For breast cancer, clinically important subtypes are well characterized at the molecular level in terms of gene expression profiles. In addition, signaling pathways in breast cancer have been extensively studied as therapeutic targets due to their roles in tumor growth and metastasis. However, it is challenging to put signaling pathways and gene expression profiles together to characterize biological mechanisms of breast cancer subtypes since many signaling events result from post-translational modifications, rather than gene expression differences. We designed a logic-based computational framework to explain the differences in gene expression profiles among breast cancer subtypes using Pathway Logic and transcriptional network information. Pathway Logic is a rewriting-logic-based formal system for modeling biological pathways including post-translational modifications. Our method demonstrated its utility by constructing subtype-specific path from key receptors (TNFR, TGFBR1 and EGFR) to key transcription factor (TF) regulators (RELA, ATF2, SMAD3 and ELK1) and identifying potential association between pathways via TFs in basal-specific paths, which could provide a novel insight on aggressive breast cancer subtypes. Codes and results are available at http://epigenomics.snu.ac.kr/PL/.

Activation of RSK by phosphomimetic substitution in the activation loop is prevented by structural constraints

The activation of the majority of AGC kinases is regulated by two phosphorylation events on two conserved serine/threonine residues located on the activation loop and on the hydrophobic motif, respectively. In AGC kinase family, phosphomimetic substitutions with aspartate or glutamate, leading to constitutive activation, have frequently occurred at the hydrophobic motif site. On the contrary, phosphomimetic substitutions in the activation loop are absent across the evolution of AGC kinases. This observation is explained by the failure of aspartate and glutamate to mimic phosphorylatable serine/threonine in this regulatory site. By detailed 3D structural simulations of RSK2 and further biochemical evaluation in cells, we show that the phosphomimetic residue on the activation loop fails to form a critical salt bridge with R114, necessary to reorient the αC-helix and to activate the protein. By a phylogenetic analysis, we point at a possible coevolution of a phosphorylatable activation loop and the presence of a conserved positively charged amino acid on the αC-helix. In sum, our analysis leads to the unfeasibility of phosphomimetic substitution in the activation loop of RSK and, at the same time, highlights the peculiar structural role of activation loop phosphorylation.

Proteomic Analysis Reveals a Role for RSK in p120-catenin Phosphorylation and Melanoma Cell-Cell Adhesion

The RAS/mitogen-activated protein kinase (MAPK) signaling pathway regulates various biological functions, including cell survival, proliferation and migration. This pathway is frequently deregulated in cancer, including melanoma, which is the most aggressive form of skin cancer. RSK (p90 ribosomal S6 kinase) is a MAPK-activated protein kinase required for melanoma growth and proliferation, but relatively little is known about its function and the nature of its cellular partners. In this study, we used a proximity-based labeling approach to identify RSK proximity partners in cells. We identified many potential RSK-interacting proteins, including p120ctn (p120-catenin), which is an essential component of adherens junction (AJ). We found that RSK phosphorylates p120ctn on Ser320, which appears to be constitutively phosphorylated in melanoma cells. We also found that RSK inhibition increases melanoma cell-cell adhesion, suggesting that constitutive RAS/MAPK signaling negatively regulates AJ integrity. Together, our results indicate that RSK plays an important role in the regulation of melanoma cell-cell adhesion.

ARHGEF12 regulates erythropoiesis and is involved in erythroid regeneration after chemotherapy in acute lymphoblastic leukemia patients

Hematopoiesis is a finely regulated process in vertebrates under both homeostatic and stress conditions. By whole exome sequencing, we studied the genomics of acute lymphoblastic leukemia (ALL) patients who needed multiple red blood cell (RBC) transfusions after intensive chemotherapy treatment. ARHGEF12, encoding a RhoA guanine nucleotide exchange factor, was found to be associated with chemotherapy-induced anemia by genome-wide association study analyses. A single nucleotide polymorphism (SNP) of ARHGEF12 located in an intron predicted to be a GATA1 binding site, rs10892563, is significantly associated with patients who need RBC transfusion (P=3.469E-03, odds ratio 5.864). A luciferase reporter assay revealed that this SNP impairs GATA1-mediated trans-regulation of ARHGEF12, and quantitative polymerase chain reaction studies confirmed that the homozygotes status is associated with an approximately 61% reduction in ARHGEF12 expression (P=0.0088). Consequently, erythropoiesis was affected at the pro-erythroblast phases. The role of ARHGEF12 and its homologs in erythroid differentiation was confirmed in human K562 cells, mouse 32D cells and primary murine bone marrow cells. We further demonstrated in zebrafish by morpholino-mediated knockdown and CRISPR/Cas9-mediated knockout of arhgef12 that its reduction resulted in erythropoiesis defects. The p38 kinase pathway was affected by the ARHGEF12-RhoA signaling in K562 cells, and consistently, the Arhgef12-RhoA-p38 pathway was also shown to be important for erythroid differentiation in zebrafish as active RhoA or p38 readily rescued the impaired erythropoiesis caused by arhgef12 knockdown. Finally, ARHGEF12-mediated p38 activity also appeared to be involved in phenotypes of patients of the rs10892563 homozygous genotype. Our findings present a novel SNP of ARHGEF12 that may involve ARHGEF12-RhoA-p38 signaling in erythroid regeneration in ALL patients after chemotherapy.

RhoC: a fascinating journey from a cytoskeletal organizer to a Cancer stem cell therapeutic target

Tumor heterogeneity results in differential response to therapy due to the existence of plastic tumor cells, called cancer stem cells (CSCs), which exhibit the property of resistance to therapy, invasion and metastasis. These cells have a distinct, signaling network active at every stage of progression. It is difficult to envisage that the CSCs will have a unique set of signaling pathways regulating every stage of disease progression. Rather, it would be easier to believe that a single pivotal pathway having significant contribution at every stage, which can further turn on a battery of signaling mechanisms specific to that stage, would be instrumental in regulating the signaling network, enabling easy transition from one state to another. In this context, we discuss the role of RhoC which has contributed to several phenotypes during tumor progression.

RhoC (Ras homolog gene family member C) has been widely reported to regulate actin organization. It has been shown to impact the motility of cancer cells, resultantly affecting invasion and metastasis, and has contributed to carcinoma progression of the breast, pancreas, lung, ovaries and cervix, among several others. The most interesting finding has been its indispensable role in metastasis. Also, it has the ability to modulate various other phenotypes like angiogenesis, motility, invasion, metastasis, and anoikis resistance. These observations suggest that RhoC imparts the plasticity required by tumor cells to exhibit such diverse functions based on microenvironmental cues. This was further confirmed by recent reports which show that it regulates cancer stem cells in breast, ovary and head and neck cancers. Studies also suggest that the inhibition of RhoC results in abolition of advanced tumor phenotypes.

Our review throws light on how RhoC, which is capable of modulating various phenotypes may be the apt core signaling candidate regulating disease progression. Additionally, mice studies show that RhoC is not essential for embryogenesis, giving scope for its development as a possible therapeutic target. This review thus stresses on the need to understand the protein and its functioning in greater detail to enable its development as a stem cell marker and a possible therapeutic target.

A novel function of artesunate on inhibiting migration and invasion of fibroblast-like synoviocytes from rheumatoid arthritis patients

Introduction

Anti-malarial drug artesunate can suppress inflammation and prevent cartilage and bone destruction in collagen-induced arthritis model in rats—suggesting it may be a potent drug for rheumatoid arthritis (RA) therapy. We aimed to investigate its effect on the invasive property of fibroblast-like synoviocytes (FLS) from patients with RA.

Methods

Synovial tissues were obtained by closed needle biopsy from active RA patients, and FLS were isolated and cultured in vitro. RA-FLS were treated with artesunate at various concentrations, while methotrexate or hydroxychloroquine was employed as comparator drugs. Cell viability, proliferation, cell cycle, apoptosis, migration, invasion, and pseudopodium formation of RA-FLS were assessed by CCK-8 assays, EdU staining, Annexin V-FITC/PI staining, transwell assays, or F-actin staining, respectively. Further, relative changes of expressed proteases were analyzed by Proteome profiler human protease array and verified by quantitative real-time PCR (qPCR), Western blot, and ELISA. The expression of signaling molecules of MAPK, NF-κB, AP-1, and PI3K/Akt pathways were measured by qPCR and Western blot. PDK-1 knockdown by specific inhibitor AR-12 or siRNA transfection was used to verify the pharmacological mechanism of artesunate on RA-FLS.

Results

Artesunate significantly inhibited the migration and invasion of RA-FLS in a dose-dependent manner with or without TNF-α stimulation. The effect was mediated through artesunate inhibition of MMP-2 and MMP-9 production, and pre-treatment with exogenous MMP-9 reversed the inhibitory effect of artesunate on RA-FLS invasion. Artesunate had a stronger inhibitory effect on migration and invasion of RA-FLS as well as greater anti-inflammatory effect than those of hydroxychloroquine. Similar inhibitory effect was detected between artesunate and methotrexate, and synergy was observed when combined. Mechanistically, artesunate significantly inhibited PDK-1 expression as well as Akt and RSK2 phosphorylation—in a similar manner to PDK-1-specific inhibitor AR-12 or PDK-1 knockdown by siRNA transfection. This inhibition results in suppression of RA-FLS migration and invasion as well as decreased MMP-2 and MMP-9 expression.

Conclusions

Our study demonstrates artesunate is capable of inhibiting migration and invasion of RA-FLS through suppression of PDK1-induced activation of Akt and RSK2 phosphorylation—suggesting that artesunate may be a potential disease-modifying anti-rheumatic drug for RA.

Electronic supplementary material

The online version of this article (10.1186/s13075-019-1935-6) contains supplementary material, which is available to authorized users.

p90 ribosomal S6 kinase (RSK) phosphorylates myosin phosphatase and thereby controls edge dynamics during cell migration

Cell migration is essential to embryonic development, wound healing, and cancer cell dissemination. Cells move via leading-edge protrusion, substrate adhesion, and retraction of the cell's rear. The molecular mechanisms by which extracellular cues signal to the actomyosin cytoskeleton to control these motility mechanics are poorly understood. The growth factor-responsive and oncogenically activated protein extracellular signal-regulated kinase (ERK) promotes motility by signaling in actin polymerization-mediated edge protrusion. Using a combination of immunoblotting, co-immunoprecipitation, and myosin-binding experiments and cell migration assays, we show here that ERK also signals to the contractile machinery through its substrate, p90 ribosomal S6 kinase (RSK). We probed the signaling and migration dynamics of multiple mammalian cell lines and found that RSK phosphorylates myosin phosphatase–targeting subunit 1 (MYPT1) at Ser-507, which promotes an interaction of Rho kinase (ROCK) with MYPT1 and inhibits myosin targeting. We find that by inhibiting the myosin phosphatase, ERK and RSK promote myosin II–mediated tension for lamella expansion and optimal edge dynamics for cell migration. These findings suggest that ERK activity can coordinately amplify both protrusive and contractile forces for optimal cell motility.

Rewiring of RSK-PDZ Interactome by Linear Motif Phosphorylation

Phosphorylation of short linear peptide motifs is a widespread process for the dynamic regulation of protein-protein interactions. However, the global impact of phosphorylation events on the protein-protein interactome is rarely addressed. The disordered C-terminal tail of ribosomal S6 kinase 1 (RSK1) binds to PDZ domain-containing scaffold proteins, and it harbors a phosphorylatable PDZ-binding motif (PBM) responsive to epidermal growth factor stimulation. Here, we examined binding of two versions of the RSK1 PBM, either phosphorylated or unphosphorylated at position -3, to almost all (95%) of the 266 PDZ domains of the human proteome. PBM phosphorylation dramatically altered the PDZ domain-binding landscape of RSK1, by strengthening or weakening numerous interactions to various degrees. The RSK-PDZome interactome analyzed in this study reveals how linear motif-based phospho-switches convey stimulus-dependent changes in the context of related network components.

Druggable targets in the Rho pathway and their promise for therapeutic control of blood pressure

The prevalence of high blood pressure (also known as hypertension) has steadily increased over the last few decades. Known as a silent killer, hypertension increases the risk for cardiovascular disease and can lead to stroke, heart attack, kidney failure and associated sequela. While numerous hypertensive therapies are currently available, it is estimated that only half of medicated patients exhibit blood pressure control. This signifies the need for a better understanding of the underlying cause of disease and for more effective therapies. While blood pressure homeostasis is very complex and involves the integrated control of multiple body systems, smooth muscle contractility and arterial resistance are important contributors. Strong evidence from pre-clinical animal models and genome-wide association studies indicate that smooth muscle contraction and BP homeostasis are governed by the small GTPase RhoA and its downstream target, Rho kinase. In this review, we summarize the signaling pathways and regulators that impart tight spatial-temporal control of RhoA activity in smooth muscle cells and discuss current therapeutic strategies to target these RhoA pathway components. We also discuss known allelic variations in the RhoA pathway and consider how these polymorphisms may affect genetic risk for hypertension and its clinical manifestations.

Burkholderia Lethal Factor 1, a Novel Anti-Cancer Toxin, Demonstrates Selective Cytotoxicity in MYCN-Amplified Neuroblastoma Cells

Immunotoxins are being investigated as anti-cancer therapies and consist of a cytotoxic enzyme fused to a cancer targeting antibody. All currently used toxins function via the inhibition of protein synthesis, making them highly potent in both healthy and transformed cells. This non-specific cell killing mechanism causes dose-limiting side effects that can severely limit the potential of immunotoxin therapy. In this study, the recently characterised bacterial toxin Burkholderia lethal factor 1 (BLF1) is investigated as a possible alternative payload for targeted toxin therapy in the treatment of neuroblastoma. BLF1 inhibits translation initiation by inactivation of eukaryotic initiation translation factor 4A (eIF4A), a putative anti-cancer target that has been shown to regulate a number of oncogenic proteins at the translational level. We show that cellular delivery of BLF1 selectively induces apoptosis in neuroblastoma cells that display MYCN amplification but has little effect on non-transformed cells. Future immunotoxins based on this enzyme may therefore have higher specificity towards MYCN-amplified cancer cells than more conventional ribosome-inactivating proteins, leading to an increased therapeutic window and decreased side effects.

Growth Concerns in Coffin-Lowry Syndrome: A Case Report and Literature Review

Mutation of RPS6KA3 can induce Coffin-Lowry syndrome, an X-linked syndrome. The case here reported manifests its signature characteristic of short stature, facial dysmorphism, development retardation, hearing defect. The mutation of RPS6KA3 we detected by NGS analysis is c.2185 C > T. The short stature is a noteworthy problem we discuss here to improve the patient's growth and development. The efficacy and safety of application of growth hormone analogs on patients with CLS are not confirmed and need to be carefully considered.