Nalbuphine suppresses leukemia stem cells and acts synergistically with chemotherapy drugs via inhibiting Ras/Raf/Mek/Erk pathway

AIMS

Retrospective clinical studies have shown that opioids could potentially affect the risk of cancer recurrence and metastasis. Better understanding of the effects of opioids on cancer will help to select the optimal anesthetic regimens to achieve better outcomes in cancer patients.

BACKGROUND

Increasing evidence has shown the direct effects of opioids on bulk cancer cells and cancer stem cells. Opioid such as nalbuphine is approved to control cancer-associated pain but little is known on their possible cancer effects.

OBJECTIVE

To assess the biological effects of nalbuphine on acute myeloid leukemia (AML) differentiated and stem/progenitor CD34+ cells.

METHOD

AML CD34+ cells were isolated with colony formation, growth and apoptosis assays performed. Biochemical and immunoblotting analyses were conducted in AML cells exposed to nalbuphine.

RESULT

Nalbuphine at clinically relevant concentrations was active against a panel of AML cell lines with varying IC50. Importantly, nalbuphine augmented the efficacy of cytarabine and daunorubicin in decreasing AML cell viability/growth. Besides bulk AML cells, we noted that nalbuphine was effective and selective in decreasing viability and colony formation of AML CD34+ cells while sparing normal hematopoietic CD34+ cells. The action of nalbuphine on AML cells is not associated with opioid receptors but via inhibiting Ras/Raf/MEK/ERK signaling pathway. Overexpression of constitutively active Ras partially but significantly reversed the inhibitory effects of nalbuphine on AML cells.

CONCLUSION

Our findings reveal the selective anti-AML activity of nalbuphine and its ability in inhibiting Ras signaling. Our work suggests that nalbuphine may be beneficial for leukemia patients.

Acarbose Protects Glucolipotoxicity-Induced Diabetic Nephropathy by Inhibiting Ras Expression in High-Fat Diet-Fed db/db Mice

Diabetic nephropathy (DN) exacerbates renal tissue damage and is a major cause of end-stage renal disease. Reactive oxygen species play a vital role in hyperglycemia-induced renal injury. This study examined whether the oral hypoglycemic drug acarbose (Ab) could attenuate the progression of DN in type 2 diabetes mellitus mice. In this study, 50 mg/kg body weight of Ab was administered to high-fat diet (HFD)-fed db/db mice. Their body weight was recorded every week, and the serum glucose concentration was monitored every 2 weeks. Following their euthanasia, the kidneys of mice were analyzed through hematoxylin and eosin, periodic acid Schiff, Masson's trichrome, and immunohistochemistry (IHC) staining. The results revealed that Ab stabilized the plasma glucose and indirectly improved the insulin sensitivity and renal functional biomarkers in diabetic mice. In addition, diabetes-induced glomerular hypertrophy, the saccharide accumulation, and formation of collagen fiber were reduced in diabetic mice receiving Ab. Although the dosages of Ab cannot decrease the blood sugar in db/db mice, our results indicate that Ab alleviates glucolipotoxicity-induced DN by inhibiting kidney fibrosis-related proteins through the Ras/ERK pathway.

At the Research Frontiers of Small GTPases

Small GTPases act as molecular switches in regulating a myriad of cellular signaling, cytoskeletal dynamics, vesicular trafficking, and membrane/organelle transport processes. Here, I provide an editorial overview of papers collected in this Special Issue on the "Regulation and Function of Small GTPases 2.0".

EGFR signal transduction is downregulated in C. elegans vulval precursor cells during dauer diapause

Caenorhabditis elegans larvae display developmental plasticity in response to environmental conditions: in adverse conditions, second-stage larvae enter a reversible, long-lived dauer stage instead of proceeding to reproductive adulthood. Dauer entry interrupts vulval induction and is associated with a reprogramming-like event that preserves the multipotency of vulval precursor cells (VPCs), allowing vulval development to reinitiate if conditions improve. Vulval induction requires the LIN-3/EGF-like signal from the gonad, which activates EGFR-Ras-ERK signal transduction in the nearest VPC, P6.p. Here, using a biosensor and live imaging we show that EGFR-Ras-ERK activity is downregulated in P6.p in dauers. We investigated this process using gene mutations or transgenes to manipulate different steps of the pathway, and by analyzing LET-23/EGFR subcellular localization during dauer life history. We found that the response to EGF is attenuated at or upstream of Ras activation, and discuss potential membrane-associated mechanisms that could achieve this. We also describe other findings pertaining to the maintenance of VPC competence and quiescence in dauer larvae. Our analysis indicates that VPCs have L2-like and unique dauer stage features rather than features of L3 VPCs in continuous development.

Conformational Dynamics Allows Sampling of an "Active-like" State by Oncogenic K-Ras-GDP

Mutations in K-Ras GTPase replacing Gly12 with either Asp or Val are common in cancer. These mutations decelerate intrinsic and catalyzed GTP hydrolysis, leading to accumulation of K-Ras-GTP in cells. Signaling cascades initiated by K-Ras-GTP promote cell proliferation, survival, and invasion. Despite functional differences between the most frequent G12D mutation and the most aggressive and chemotherapy resistant G12V mutation, their long-suspected distinct structural features remain elusive. Using NMR, X-ray structures, and computational methods, we found that oncogenic mutants of K-Ras4B, the predominant splice variant of K-Ras, exhibit distinct conformational dynamics when GDP-bound, visiting the "active-like" conformational state similar to the one observed in GTP-bound K-Ras. This behavior distinguishes G12V from wild type and G12D K-Ras4B-GDP. The likely reason is hydrophobic interactions between the aliphatic sidechain of V12 and the Switch II region of K-Ras4B^G12V-GDP, which are distinct in K-Ras4B^G12D-GDP. In the X-ray structures, crystal contacts reduce the dynamics of the sidechain at position 12 by stabilizing the Switch I region of the protein. This explains why structural differences between G12V and G12D K-Ras have yet not been reported. Together, our results suggest a previously unknown mechanism of K-Ras activation. This mechanism relies on conformational dynamics caused by specific oncogenic mutations in the GDP-bound state. Our findings also imply that the therapeutic strategies decreasing the level of K-Ras-GTP by interfering with nucleotide exchange or by expediting GTP hydrolysis may work differently in different oncogenic mutants.

The structural basis of BCR-ABL recruitment of GRB2 in chronic myelogenous leukemia

BCR-ABL drives chronic myeloid leukemia (CML). BCR binding to GRB2 transduces signaling via the Ras/MAPK pathway. Despite considerable data confirming the binding, molecular-level understanding of exactly how the two proteins interact, and especially, what are the determinants of the specificity of the SH2^GRB2 domain-pBCR recognition are still open questions. Yet, this is vastly important for understanding binding selectivity, and for predicting the phosphorylated receptors, or peptides, that are likely to bind. Here, we uncover these determinants and ascertain to what extent they relate to the affinity of the interaction. Toward this end, we modeled the complexes of the phosphorylated BCR (pBCR) and SH2^GRB2 and other pY/Y-peptide-SH2 complexes and compared their specificity and affinity. We observed that pBCR's ₁₇₆FpYVNV₁₈₀ motif is favorable and specific to SH2^GRB2, similar to pEGFR, but not other complexes. SH2^GRB2 contains two binding pockets: pY-binding recognition pocket triggers binding, and the specificity pocket whose interaction is governed by N179 in pBCR and W121 in SH2^GRB2. Our proposed motif with optimal affinity to SH2^GRB2 is E/D-pY-E/V-N-I/L. Collectively, we provide the structural basis of BCR-ABL recruitment of GRB2, outline its specificity hallmarks, and delineate a blueprint for prediction of BCR-binding scaffolds and for therapeutic peptide design.

Rho-Rho-Kinase Regulates Ras-ERK Signaling Through SynGAP1 for Dendritic Spine Morphology

The structural plasticity of dendritic spines plays a critical role in NMDA-induced long-term potentiation (LTP) in the brain. The small GTPases RhoA and Ras are considered key regulators of spine morphology and enlargement. However, the regulatory interaction between RhoA and Ras underlying NMDA-induced spine enlargement is largely unknown. In this study, we found that Rho-kinase/ROCK, an effector of RhoA, phosphorylated SynGAP1 (a synaptic Ras-GTPase activating protein) at Ser842 and increased its interaction with 14-3-3ζ, thereby activating Ras-ERK signaling in a reconstitution system in HeLa cells. We also found that the stimulation of NMDA receptor by glycine treatment for LTP induction stimulated SynGAP1 phosphorylation, Ras-ERK activation, spine enlargement and SynGAP1 delocalization from the spines in striatal neurons, and these effects were prevented by Rho-kinase inhibition. Rho-kinase-mediated phosphorylation of SynGAP1 appeared to increase its dissociation from PSD95, a postsynaptic scaffolding protein located at postsynaptic density, by forming a complex with 14-3-3ζ. These results suggest that Rho-kinase phosphorylates SynGAP1 at Ser842, thereby activating the Ras-ERK pathway for NMDA-induced morphological changes in dendritic spines.

Emerging RAS-directed therapies for cancer

RAS oncogenes are the most commonly mutated oncogenes in human cancer, and RAS-mutant cancers represent a major burden of human disease. Though these oncogenes were discovered decades ago, recent years have seen major advances in understanding of their structure and function, including the therapeutic and prognostic significance of diverse isoforms. Targeting of these mutations has proven difficult, despite some successes with inhibition of RAS effector signalling. More recently, direct RAS inhibition has been achieved in a trial setting. While this has yet to be translated to everyday clinical practice, this development carries much promise. This review summarizes the diverse approaches that have been taken to RAS inhibition and then focuses on the most recent developments in direct inhibition of KRAS(G12C).

Structural insights into Ras regulation by SIN1

Both the mTORC2 and Ras-ERK pathways respond to growth factor stimulation and play critical roles in cell growth and proliferation, disarray of these pathways leads to many diseases, especially cancer. These two signaling pathways crosstalk at many levels; recently it's become clear that the SIN1 component of mTORC2 could interact with Ras family small GTPases, but how these two proteins interact at the molecular level and the functional outcomes of this interaction remain to be addressed. In this work we determined the high-resolution structure of Ras-SIN1 complexes and revealed the detailed interaction mechanism. We also showed that Ras-SIN1 association inhibits insulin-induced ERK activation. Insights from this work could improve our understanding of the disease-causing mechanism of errant mTORC2 or Ras proteins.

Over the years it has been established that SIN1, a key component of mTORC2, could interact with Ras family small GTPases through its Ras-binding domain (RBD). The physical association of Ras and SIN1/mTORC2 could potentially affect both mTORC2 and Ras-ERK pathways. To decipher the precise molecular mechanism of this interaction, we determined the high-resolution structures of HRas/KRas-SIN1 RBD complexes, showing the detailed interaction interface. Mutation of critical interface residues abolished Ras-SIN1 interaction and in SIN1 knockout cells we demonstrated that Ras-SIN1 association promotes SGK1 activity but inhibits insulin-induced ERK activation. With structural comparison and competition fluorescence resonance energy transfer (FRET) assays we showed that HRas-SIN1 RBD association is much weaker than HRas-Raf1 RBD but is slightly stronger than HRas-PI3K RBD interaction, providing a possible explanation for the different outcome of insulin or EGF stimulation. We also found that SIN1 isoform lacking the PH domain binds stronger to Ras than other longer isoforms and the PH domain appears to have an inhibitory effect on Ras-SIN1 binding. In addition, we uncovered a Ras dimerization interface that could be critical for Ras oligomerization. Our results advance our understanding of Ras-SIN1 association and crosstalk between growth factor-stimulated pathways.

A two-component protein condensate of the EGFR cytoplasmic tail and Grb2 regulates Ras activation by SOS at the membrane

We reconstitute a phosphotyrosine-mediated protein condensation phase transition of the ∼200 residue cytoplasmic tail of the epidermal growth factor receptor (EGFR) and the adaptor protein, Grb2, on a membrane surface. The phase transition depends on phosphorylation of the EGFR tail, which recruits Grb2, and crosslinking through a Grb2-Grb2 binding interface. The Grb2 Y160 residue plays a structurally critical role in the Grb2-Grb2 interaction, and phosphorylation or mutation of Y160 prevents EGFR:Grb2 condensation. By extending the reconstitution experiment to include the guanine nucleotide exchange factor, SOS, and its substrate Ras, we further find that the condensation state of the EGFR tail controls the ability of SOS, recruited via Grb2, to activate Ras. These results identify an EGFR:Grb2 protein condensation phase transition as a regulator of signal propagation from EGFR to the MAPK pathway.

Molecular dissection on inhibition of Ras-induced cellular senescence by small t antigen of SV40

Simian virus 40 (SV40) is a potentially oncogenic virus of monkey origin. Transmission, prevalence, and pathogenicity rates of SV40 are unclear, but infection can occur in humans, for example individuals with high contact with rhesus macaques and individuals that received contaminated early batches of polio vaccines in 1950-1963. In addition, several human polyomaviruses, proven carcinogenic, are also highly common in global populations. Cellular senescence is a major mechanism of cancer prevention in vivo. Hyperactivation of Ras usually induces cellular senescence rather than cell transformation. Previous studies suggest small t antigen (ST) of SV40 may interfere with cellular senescence induced by Ras. In the current study, ST was demonstrated to inhibit Ras-induced cellular senescence (RIS) and accumulation of DNA damage in Ras-activated cells. In addition, ST suppressed the signal transmission from BRaf to MEK and thus blocked the downstream transmission of the activated Ras signal. B56γ knockdown mimicked the inhibitory effects of ST overexpression on RIS. Furthermore, KSR1 knockdown inhibited Ras activation and the subsequent cellular senescence. Further mechanism studies indicated that the phosphorylation level of KSR1 rather than the levels of the total protein regulates the activation of Ras signaling pathway. In sum, ST inhibits the continuous hyperactivation of Ras signals by interfering with the normal functions of PP2A-B56γ of dephosphorylating KSR1, thus inhibiting the occurrence of cellular senescence. Although the roles of SV40 in human carcinogenesis are controversial so far, our study has shown that ST of polyomaviruses has tumorigenic potential by inhibiting oncogene-induced senescence (OIS) as a proof of concept.

Orai1 downregulation causes proliferation reduction and cell cycle arrest via inactivation of the Ras-NF-κB signaling pathway in osteoblasts

Background

The purpose of this study was to determine the role of Orai1 in the regulation of the proliferation and cell cycle of osteoblasts.

Methods

The expression of Orai1 was inhibited by Orai1 small interfering RNA (siRNA) in MC3T3-E1 cells. Following Orai1 downregulation, cell proliferation and cell cycle were examined. Furthermore, the expression of cyclin D1, cyclin E, CDK4, and CDK6 was analyzed. The activity of the Ras-NF-κB signaling pathway was investigated to identify the role of Orai1 in the regulation of osteoblast proliferation.

Results

Orai1 was successfully downregulated in MC3T3-E1 cells by the Orai1 siRNA transfection (p < 0.05). We found that MC3T3-E1 cell proliferation was decreased, and the cell cycle was arrested by Orai1 downregulation (p < 0.05). Additionally, the expression of cyclin D1 was decreased by Orai1 downregulation (p < 0.05), as was the activity of the Ras-NF-κB signaling pathway (p < 0.05). Orai1 siRNA did not further reduce cell proliferation, the proportion of cells in the S phase, and cyclin D1 expression after chemical blockage of the Ras signaling pathway in MC3T3-E1 cells (p > 0.05).

Conclusions

The results reveal that Orai1 downregulation may reduce cyclin D1 expression by inactivating the Ras-NF-κB signaling pathway thus blocking osteoblast proliferation and cell cycle.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05311-y.

Ultrastructural Characteristics of Finger-Like Membrane Protrusions in Cell Competition

A small number of oncogenic mutated cells sporadically arise within the epithelial monolayer. Newly emerging Ras- or Src-transformed epithelial cells are often apically eliminated during competitive interactions between normal and transformed cells. Our recent electron microscopy (EM) analyses revealed that characteristic finger-like membrane protrusions are formed at the interface between normal and RasV12-transformed cells via the cdc42–formin-binding protein 17 (FBP17) pathway, potentially playing a positive role in intercellular recognition during apical extrusion. However, the spatial distribution and ultrastructural characteristics of finger-like protrusions remain unknown. In this study, we performed both X–Y and X–Z EM analyses of finger-like protrusions during the apical extrusion of RasV12-transformed cells. Quantification of the distribution and widths of the protrusions showed comparable results between the X–Y and X–Z sections. Finger-like protrusions were observed throughout the cell boundary between normal and RasV12 cells, except for apicalmost tight junctions. In addition, a non-cell-autonomous reduction in protrusion widths was observed between RasV12 cells and surrounding normal cells under the mix culture condition. In the finger-like protrusions, intercellular adhesions via thin electron-dense plaques were observed, implying that immature and transient forms of desmosomes, adherens junctions or unknown weak adhesions were distributed. Interestingly, unlike RasV12-transformed cells, Src-transformed cells form fewer evident protrusions, and FBP17 in Src cells is dispensable for apical extrusion. Collectively, these results suggest that the dynamic reorganization of intercellular adhesions via finger-like protrusions may positively control cell competition between normal and RasV12-transformed cells. Furthermore, our data indicate a cell context–dependent diversity in the modes of apical extrusion.

Reconstruction and analysis of a large-scale binary Ras-effector signaling network

BACKGROUND

Ras is a key cellular signaling hub that controls numerous cell fates via multiple downstream effector pathways. While pathways downstream of effectors such as Raf, PI3K and RalGDS are extensively described in the literature, how other effectors signal downstream of Ras is often still enigmatic.

METHODS

A comprehensive and unbiased Ras-effector network was reconstructed downstream of 43 effector proteins (converging onto 12 effector classes) using public pathway and protein-protein interaction (PPI) databases. The output is an oriented graph of pairwise interactions defining a 3-layer signaling network downstream of Ras. The 2290 proteins comprising the network were studied for their implication in signaling crosstalk and feedbacks, their subcellular localizations, and their cellular functions.

RESULTS

The final Ras-effector network consists of 2290 proteins that are connected via 19,080 binary PPIs, increasingly distributed across the downstream layers, with 441 PPIs in layer 1, 1660 in layer 2, and 16,979 in layer 3. We identified a high level of crosstalk among proteins of the 12 effector classes. A class-specific Ras sub-network was generated in CellDesigner (.xml file) and a functional enrichment analysis thereof shows that 58% of the processes have previously been associated to a respective effector pathway, with the remaining providing insights into novel and unexplored functions of specific effector pathways.

CONCLUSIONS

Our large-scale and cell general Ras-effector network is a crucial steppingstone towards defining the network boundaries. It constitutes a 'reference interactome' and can be contextualized for specific conditions, e.g. different cell types or biopsy material obtained from cancer patients. Further, it can serve as a basis for elucidating systems properties, such as input-output relationships, crosstalk, and pathway redundancy. Video Abstract.

Cardiac decompensation and promiscuous prenylation of small GTPases in cardiomyocytes in response to local mevalonate pathway disruption

Investigations of major mevalonate pathway enzymes have demonstrated the importance of local isoprenoid synthesis in cardiac homeostasis. Farnesyl diphosphate synthase (FPPS) synthesizes isoprenoid precursors needed for cholesterol biosynthesis and protein prenylation. Wang, Zhang, Chen et al, in a recently published article in The Journal of Pathology, elegantly elucidated the pathological outcomes of FPPS deficiency in cardiomyocytes, which paradoxically resulted in increased prenylation of the small GTPases Ras and Rheb. Cardiomyocyte FPPS depletion caused severe dilated cardiomyopathy that was associated with enhanced GTP-loading and abundance of Ras and Rheb in lipidated protein-enriched cardiac fractions and robust activation of downstream hypertrophic ERK1/2 and mTOR signaling pathways. Cardiomyopathy and activation of ERK1/2 and mTOR caused by loss of FPPS were ameliorated by inhibition of farnesyltransferase, suggesting that impairment of FPPS activity results in promiscuous activation of Ras and Rheb through non-canonical actions of farnesyltransferase. Here, we discuss the findings and adaptive signaling mechanisms in response to disruption of local cardiomyocyte mevalonate pathway activity, highlighting how alteration in a key branch point in the mevalonate pathway affects cardiac biology and function and perturbs protein prenylation, which might unveil novel strategies and intricacies of targeting the mevalonate pathway to treat cardiovascular diseases. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Zinc ions negatively regulate proapoptotic signaling in cells expressing oncogenic mutant Ras

Mutational activation of the Ras family of proto-oncogenes promotes cell survival and proliferation. Studies using cells cultured in vitro have shown that ectopic expression of constitutively active Ras suppresses apoptosis induced by serum deprivation. However, in some cellular contexts, constitutively active Ras exerts the opposite effects, including apoptosis of serum-starved embryonic fibroblasts. Such observations first came over two decades ago, but the molecular mechanisms by which mutant Ras increases the susceptibility of cells to serum deprivation leading to apoptosis are still not fully understood. To revisit this issue, I investigate the effects of serum depletion and mutant Ras expression on intracellular signaling and transcriptome of cells carrying an inducible allele of constitutively active mutant Hras (Hras^G12V). I identify zinc ions (Zn²⁺) as a serum factor that suppresses proapoptotic signaling in cells expressing Hras^G12V. Mechanistically, Hras^G12V expression along with Zn²⁺ deficiency activates c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK), which are required for caspase-3 activation involved in the induction of cell death. Transcriptome analyses suggest that Hras^G12V induces the unfolded protein response (UPR). Further analyses of intracellular signaling biomolecules related to the UPR indicate that Hras^G12V activates inositol-requiring protein 1 (IRE1), which synergizes with Zn²⁺ deficiency to activate JNK and p38 MAPK signaling. These results provide insights into a role of Zn²⁺ that counteracts proapoptotic signaling activated by mutationally activated Ras.

PKC is an indispensable factor in promoting environmental toxin chromium-mediated transformation and drug resistance

Hexavalent chromium [Cr(VI)] pollution is a serious environmental problem, due to not only its toxicity but also carcinogenesis. Although studies reveal several features of Cr(VI)-induced carcinogenesis, the underlying mechanisms of how Cr(VI) orchestrates multiple mitogenic pathways to promote tumor initiation and progression remain not fully understood. Src/Ras and other growth-related pathways are shown to be key players in Cr(VI)-initiated tumor prone actions. The role of protein kinase C (PKC, an important signal transducer) in Cr(VI)-mediated carcinogenesis has not been thoroughly investigated. In this study, using human bronchial/lung epithelial cells and keratinocytes, we demonstrate that PKC activity is increased by transient or chronic Cr(VI) exposure, which plays no role in the activation of Src/Ras signaling and ROS upregulation by this metal toxin. PKC in chronic Cr(VI)-treated cells stabilizes Bcl-2 to mitigate doxorubicin (an anti-cancer drug)-mediated apoptosis. After the suppression of this kinase by GO6976 (a PKC inhibitor), the cells chronically exposed to Cr(VI) partially regain the sensitivity to doxorubicin. However, when co-suppressed PKC and Ras, the chronic Cr(VI)-treated cells become fully responsive to doxorubicin and are unable to be transformed. Taken together, our study provides a new insight into the mechanisms, in which PKC is an indispensable player and cooperates with other mitogenic pathways to achieve Cr(VI)-induced carcinogenesis as well as to establish drug resistance. The data also suggest that active PKC can serve as a potential biomarker for early detection of health damages by Cr(VI) and therapeutic target for developing new treatments for diseases caused by Cr(VI).

Drug targeting opportunities en route to Ras nanoclusters

Disruption of the native membrane organization of Ras by the farnesyltransferase inhibitor tipifarnib in the late 1990s constituted the first indirect approach to drug target Ras. Since then, our understanding of how dynamically Ras shuttles between subcellular locations has changed significantly. Ras proteins have to arrive at the plasma membrane for efficient MAPK-signal propagation. On the plasma membrane Ras proteins are organized into isoform specific proteo-lipid assemblies called nanocluster. Recent evidence suggests that Ras nanocluster have a specific lipid composition, which supports the recruitment of effectors such as Raf. Conversely, effectors possess lipid-recognition motifs, which appear to serve as co-incidence detectors for the lipid domain of a given Ras isoform. Evidence suggests that dimeric Raf proteins then co-assemble dimeric Ras in an immobile complex, thus forming the minimal unit of an active nanocluster. Here we review established and novel trafficking chaperones and trafficking factors of Ras, along with the set of lipid and protein modulators of Ras nanoclustering. We highlight drug targeting approaches and opportunities against these determinants of functional Ras membrane organization. Finally, we reflect on implications for Ras signaling in polarized cells, such as epithelia, which are a common origin of tumorigenesis.

Ras Multimers on the Membrane: Many Ways for a Heart-to-Heart Conversation

Formation of Ras multimers, including dimers and nanoclusters, has emerged as an exciting, new front of research in the 'old' field of Ras biomedicine. With significant advances made in the past few years, we are beginning to understand the structure of Ras multimers and, albeit preliminary, mechanisms that regulate their formation in vitro and in cells. Here we aim to synthesize the knowledge accrued thus far on Ras multimers, particularly the presence of multiple globular (G-) domain interfaces, and discuss how membrane nanodomain composition and structure would influence Ras multimer formation. We end with some general thoughts on the potential implications of Ras multimers in basic and translational biology.

The Amoebal Model for Macropinocytosis

Macropinocytosis is a relatively unexplored form of large-scale endocytosis driven by the actin cytoskeleton. Dictyostelium amoebae form macropinosomes from cups extended from the plasma membrane, then digest their contents and absorb the nutrients in the endo-lysosomal system. They use macropinocytosis for feeding, maintaining a high rate of fluid uptake that makes assay and experimentation easy. Mutants collected over the years identify cytoskeletal and signalling proteins required for macropinocytosis. Cups are organized around plasma membrane domains of intense PIP3, Ras and Rac signalling, proper formation of which also depends on the RasGAPs NF1 and RGBARG, PTEN, the PIP3-regulated protein kinases Akt and SGK and their activators PDK1 and TORC2, Rho proteins, plus other components yet to be identified. This PIP3 domain directs dendritic actin polymerization to the extending lip of macropinocytic cups by recruiting a ring of the SCAR/WAVE complex around itself and thus activating the Arp2/3 complex. The dynamics of PIP3 domains are proposed to shape macropinocytic cups from start to finish. The role of the Ras-PI3-kinase module in organizing feeding structures in unicellular organisms most likely predates its adoption into growth factor signalling, suggesting an evolutionary origin for growth factor signalling.

The Cross-Talk between Epigenetic Gene Regulation and Signaling Pathways Regulates Cancer Pathogenesis

Cancer begins due to uncontrolled cell division. Cancer cells are insensitive to the signals that control normal cell proliferation. This uncontrolled cell division is due to the accumulation of abnormalities in different factors associated with the cell division, including different cyclins, cell cycle checkpoint inhibitors, and cellular signaling. Cellular signaling pathways are aberrantly activated in cancer mainly due to epigenetic regulation and post-translational regulation. In this chapter, the role of epigenetic regulation in aberrant activation of PI3K/AKT, Ras, Wnt, Hedgehog, Notch, JAK/STAT, and mTOR signaling pathways in cancer progression is discussed. The role of epigenetic regulators in controlling the upstream regulatory proteins and downstream effector proteins responsible for abnormal cellular signaling-mediated cancer progression is covered in this chapter. Similarly, the role of signaling pathways in controlling epigenetic gene regulation-mediated cancer progression is also discussed. We have tried to ascertain the current status of potential epigenetic drugs targeting several epigenetic regulators to prevent different cancers.

Investigating increased hematopoietic stem cell fitness in a novel mouse model

T-cell acute lymphoblastic leukaemia (T-ALL) is a bone marrow (BM) malignancy affecting children and adults. Typically treated with chemotherapy, leukaemia remains a major death cause in people under 20 years old. Understanding molecularly altered pathways in T-ALL may lead to new therapeutic avenues in the future. Ras pathway dysregulation is common in T-ALL. We have shown elevated expression levels of the Ras guanine nucleotide exchange factor RasGRP1 in T-ALL patients, which results in constant production of active Ras (RasGTP). When leukaemia cell lines are exposed to cytokines, RasGTP levels further increase in a RasGRP1-dependent manner. How overexpressed RasGRP1 may impact primary BM cells has remained unknown. We recently published a new RoLoRiG mouse model that allows for pIpC-induced overexpression of RasGRP1 in haematopoietic cells, which can be traced with an ires-EGFP cassette. This novel model revealed that RasGRP1 overexpression bestows a fitness advantage to haematopoietic stem cells (HSCs) over wild-type cells. Intriguingly, this increased fitness only manifests in native Hematopoiesis, and not in BM transplantation (BMT) assays. In this commentary, we summarize key features of our RoLoRiG model, elaborate on BM niche importance, and discuss differences between native Hematopoiesis and BMT in the context of stem cell metabolism.

Inhibition of USP11 sensitizes gastric cancer to chemotherapy via suppressing RhoA and Ras-mediated signaling pathways

BACKGROUND

The poor outcomes in advanced gastric cancer (GC) necessitate alternative therapeutic strategy. Ubiquitin-specific protease 11 (USP11) has recently garnered attention as a therapeutic target in cancer because of its important regulatory role in cancer cell functions. Here, we revealed the expression, function and underlying molecular interactions of USP11 in gastric cancer.

METHODS

The expression of USP11 was analyzed using immunohistochemistry and ELISA. The loss-of function and gain-of function analysis of USP11 was performed using siRNA knockdown and plasmid overexpression approaches. The downstream molecules regulated by USP11 were determined using immunoblotting analysis.

RESULTS

USP11 was upregulated in ∼80% of gastric cancer patients, and the upregulation was associated with HER3 overexpression. In addition, USP11 level was not regulated by HER3 and vice versa. Functional studies demonstrated that USP11 overexpression promoted gastric cancer growth and migration, and alleviated toxicity-induced by chemotherapeutic drug. In contrast, USP11 depletion significantly inhibited gastric cancer growth, migration and survival, and augmented chemotherapeutic drug's efficacy. Gastric cancer cells with higher USP11 levels were more sensitive to USP11 inhibitions than cells with lower USP11 levels. Mechanism studies showed that USP11 depletion suppressed migration via RhoA-mediated pathway and inhibited growth and survival likely via Ras-mediated pathway.

CONCLUSIONS

Our work highlights the important role of USP11 in gastric cancer and therapeutic value of inhibiting USP11 to sensitize gastric cancer to chemotherapy.

Mulberry polyphenol extracts attenuated senescence through inhibition of Ras/ERK via promoting Ras degradation in VSMC

Ageing is one of the major risk factors of human diseases, including cancer, diabetes, and cardiovascular disease. Mulberry exhibits a wide range of functions, such as anti-oxidant, anti-inflammation, and anti-diabetes. In this study, we investigated the role of mulberry polyphenol extract (MPE) in K-Ras-induced senescence of smooth muscle cells. Forced expression of K-Ras enhanced senescence of smooth muscle A7r5 cells as shown by the elevation of β-galactosidase activity. Treatment with MPE significantly repressed the Ras, phosphorylated ERK, and β-galactosidase level. MPE triggered the association of cyclins with their corresponding cyclin-dependent protein kinases and hyperphosphorylated retinoblastoma (RB). MPE also down-regulated the levels of K-Ras-induced CDK inhibitors. MPE enhanced the phosphorylated AMP-dependent protein kinase (AMPK) and inducible nitric oxide synthase (iNOS) level in the presence of K-Ras. Pretreatment with either L-NAME or AMPK inhibitor reversed the effects of MPE. In addition, L-NAME and AMPK inhibitor repressed the MPE-induced total and phosphorylated 3-hydroxy-3-methylglutaryl coenzyme A (HMG-Co A) level. MPE repressed K-Ras-induced G0/G1 arrest, whereas L-NAME and AMPK inhibitor blocked the effects of MPE. Our results indicated that MPE recovered the K-Ras-induced senescence of vascular smooth muscle cells through iNOS and AMPK-dependent pathway. Our findings suggested that MPE may prevent ageing-induced atherosclerosis.