Dual phosphorylation of Btk by Akt/protein kinase b provides docking for 14-3-3ζ, regulates shuttling, and attenuates both tonic and induced signaling in B cells. Mol Cell Biol. 2013;33:3214-3226. [PMID: 23754751 DOI: 10.1128/MCB.00247-13]

Stabilization of 14-3-3 protein-protein interactions with Fusicoccin-A decreases alpha-synuclein dependent cell-autonomous death in neuronal and mouse models

Synucleinopathies are a group of neurodegenerative diseases without effective treatment characterized by the abnormal aggregation of alpha-synuclein (aSyn) protein. Changes in levels or in the amino acid sequence of aSyn (by duplication/triplication of the aSyn gene or point mutations in the encoding region) cause familial cases of synucleinopathies. However, the specific molecular mechanisms of aSyn-dependent toxicity remain unclear. Increased aSyn protein levels or pathological mutations may favor abnormal protein-protein interactions (PPIs) that could either promote neuronal death or belong to a coping response program against neurotoxicity. Therefore, the identification and modulation of aSyn-dependent PPIs can provide new therapeutic targets for these diseases. To identify aSyn-dependent PPIs we performed a proximity biotinylation assay based on the promiscuous biotinylase BioID2. When expressed as a fusion protein, BioID2 biotinylates by proximity stable and transient interacting partners, allowing their identification by streptavidin affinity purification and mass spectrometry. The aSyn interactome was analyzed using BioID2-tagged wild-type (WT) and pathological mutant E46K aSyn versions in HEK293 cells. We found the 14-3-3 epsilon isoform as a common protein interactor for WT and E46K aSyn. 14-3-3 epsilon correlates with aSyn protein levels in brain regions of a transgenic mouse model overexpressing WT human aSyn. Using a neuronal model in which aSyn cell-autonomous toxicity is quantitatively scored by longitudinal survival analysis, we found that stabilization of 14-3-3 protein-proteins interactions with Fusicoccin-A (FC-A) decreases aSyn-dependent toxicity. Furthermore, FC-A treatment protects dopaminergic neuronal somas in the substantia nigra of a Parkinson's disease mouse model. Based on these results, we propose that the stabilization of 14-3-3 epsilon interaction with aSyn might reduce aSyn toxicity, and highlight FC-A as a potential therapeutic compound for synucleinopathies.

Inhibition of Serum- and Glucocorticoid-Regulated Protein Kinase-1 Aggravates Imiquimod-Induced Psoriatic Dermatitis and Enhances Proinflammatory Cytokine Expression through the NF-kB Pathway

Although the anti-inflammatory effect of serum- and glucocorticoid-regulated protein kinase 1 (SGK1) has been established in other diseases, the possible regulatory role of SGK1 in psoriasis and the underlying molecular mechanisms remain largely unknown. In this study, we found that SGK1 expression was decreased in macrophages from patients with psoriasis. Moreover, a specific pharmacological SGK1 inhibitor, EMD638683, significantly enhanced imiquimod-mediated toll-like receptor 7/8 activity and proinflammatory cytokine production in RAW264.7 cells, and this result was confirmed by Sgk1 small interfering RNA. Further mechanistic data showed that SGK1 inhibition increased the phosphorylation of Bruton's agammaglobulinemia tyrosine kinase; moreover, Bruton's agammaglobulinemia tyrosine kinase inhibition abrogated the proinflammatory effects of the SGK1 inhibitor on toll-like receptor 7/8 activation, thereby validating that SGK1 inhibition enhances the toll-like receptor 7/8 pathway by increasing Bruton's agammaglobulinemia tyrosine kinase phosphorylation. In addition, our in vivo results showed that SGK1 inhibition significantly increased the secretion of proinflammatory cytokines, including IL-1β, IL-6, and TNF-α, and the infiltration of T helper 17 cells in an imiquimod-induced psoriasis mouse model. Altogether, these results show that SGK1 plays a critical role in the pathogenesis of psoriasis by modulating inflammatory responses in skin lesions, indicating that SGK1‒Bruton's agammaglobulinemia tyrosine kinase signaling could be a novel therapeutic target for the control of psoriasis.

Transcription factor TFII-I fine tunes innate properties of B lymphocytes

The ubiquitously expressed transcription factor TFII-I is a multifunctional protein with pleiotropic roles in gene regulation. TFII-I associated polymorphisms are implicated in Sjögren's syndrome and Lupus in humans and, germline deletion of the Gtf2i gene in mice leads to embryonic lethality. Here we report a unique role for TFII-I in homeostasis of innate properties of B lymphocytes. Loss of Gtf2i in murine B lineage cells leads to an alteration in transcriptome, chromatin landscape and associated transcription factor binding sites, which exhibits myeloid-like features and coincides with enhanced sensitivity to LPS induced gene expression. TFII-I deficient B cells also show increased switching to IgG3, a phenotype associated with inflammation. These results demonstrate a role for TFII-I in maintaining immune homeostasis and provide clues for GTF2I polymorphisms associated with B cell dominated autoimmune diseases in humans.

Development of a novel Bruton's tyrosine kinase inhibitor that exerts anti-cancer activities potentiates response of chemotherapeutic agents in multiple myeloma stem cell-like cells

Despite recent improvements in multiple myeloma (MM) treatment, MM remains an incurable disease and most patients experience a relapse. The major reason for myeloma recurrence is the persistent stem cell-like population. It has been demonstrated that overexpression of Bruton's tyrosine kinase (BTK) in MM stem cell-like cells is correlated with drug resistance and poor prognosis. We have developed a novel small BTK inhibitor, KS151, which is unique compared to other BTK inhibitors. Unlike ibrutinib, and the other BTK inhibitors such as acalabrutinib, orelabrutinib, and zanubrutinib that covalently bind to the C481 residue in the BTK kinase domain, KS151 can inhibit BTK activities without binding to C481. This feature of KS151 is important because C481 becomes mutated in many patients and causes drug resistance. We demonstrated that KS151 inhibits in vitro BTK kinase activities and is more potent than ibrutinib. Furthermore, by performing a semi-quantitative, sandwich-based array for 71-tyrosine kinase phosphorylation, we found that KS151 specifically inhibits BTK. Our western blotting data showed that KS151 inhibits BTK signaling pathways and is effective against bortezomib-resistant cells as well as MM stem cell-like cells. Moreover, KS151 potentiates the apoptotic response of bortezomib, lenalidomide, and panobinostat in both MM and stem cell-like cells. Interestingly, KS151 inhibits stemness markers and is efficient in inhibiting Nanog and Gli1 stemness markers even when MM cells were co-cultured with bone marrow stromal cells (BMSCs). Overall, our results show that we have developed a novel BTK inhibitor effective against the stem cell-like population, and potentiates the response of chemotherapeutic agents.

Role of receptor tyrosine kinases mediated signal transduction pathways in tumor growth and angiogenesis-New insight and futuristic vision

In the past two decades, significant progress has been made in the past two decades towards the understanding of the basic mechanisms underlying cancer growth and angiogenesis. In this context, receptor tyrosine kinases (RTKs) play a pivotal role in cell proliferation, differentiation, growth, motility, invasion, and angiogenesis, all of which contribute to tumor growth and progression. Mutations in RTKs lead to abnormal signal transductions in several pathways such as Ras-Raf, MEK-MAPK, PI3K-AKT and mTOR pathways, affecting a wide range of biological functions including cell proliferation, survival, migration and vascular permeability. Increasing evidence demonstrates that multiple kinases are involved in angiogenesis including RTKs such as vascular endothelial growth factor, platelet derived growth factor, epidermal growth factor, insulin-like growth factor-1, macrophage colony-stimulating factor, nerve growth factor, fibroblast growth factor, Hepatocyte Growth factor, Tie 1 & 2, Tek, Flt-3, Flt-4 and Eph receptors. Overactivation of RTKs and its downstream regulation is implicated in tumor initiation and angiogenesis, representing one of the hallmarks of cancer. This review discusses the role of RTKs, PI3K, and mTOR, their involvement, and their implication in pro-oncogenic cellular processes and angiogenesis with effective approaches and newly approved drugs to inhibit their unrestrained action.

The Serine/Threonine Protein Phosphatase 2A (PP2A) Regulates Syk Activity in Human Platelets

Distinct membrane receptors activate platelets by Src-family-kinase (SFK)-, immunoreceptor-tyrosine-based-activation-motif (ITAM)-dependent stimulation of spleen tyrosine kinase (Syk). Recently, we reported that platelet activation via glycoprotein (GP) VI or GPIbα stimulated the well-established Syk tyrosine (Y)-phosphorylation, but also stoichiometric, transient protein kinase C (PKC)-mediated Syk serine(S)297 phosphorylation in the regulatory interdomain-B, suggesting possible feedback inhibition. The transient nature of Syk S297 phosphorylation indicated the presence of an unknown Syk pS297 protein phosphatase. In this study, we hypothesize that the S-protein phosphatase 2A (PP2A) is responsible for Syk pS297 dephosphorylation, thereby affecting Syk Y-phosphorylation and activity in human washed platelets. Using immunoblotting, we show that specific inhibition of PP2A by okadaic acid (OA) alone leads to stoichiometric Syk S297 phosphorylation, as analyzed by Zn²⁺-Phos-tag gels, without affecting Syk Y-phosphorylation. Pharmacological inhibition of Syk by PRT060318 or PKC by GF109203X only minimally reduced OA-induced Syk S297 phosphorylation. PP2A inhibition by OA preceding GPVI-mediated platelet activation induced by convulxin extended Syk S297 phosphorylation but inhibited Syk Y-phosphorylation. Our data demonstrate a novel biochemical and functional link between the S-protein phosphatase PP2A and the Y-protein kinase Syk in human platelets, and suggest that PP2A represents a potential enhancer of GPVI-mediated Syk activity caused by Syk pS297 dephosphorylation.

Regulation of p53 by the 14-3-3 protein interaction network: new opportunities for drug discovery in cancer

Most cancers evolve to disable the p53 pathway, a key tumour suppressor mechanism that prevents transformation and malignant cell growth. However, only ~50% exhibit inactivating mutations of p53, while in the rest its activity is suppressed by changes in the proteins that modulate the pathway. Therefore, restoring p53 activity in cells in which it is still wild type is a highly attractive therapeutic strategy that could be effective in many different cancer types. To this end, drugs can be used to stabilise p53 levels by modulating its regulatory pathways. However, despite the emergence of promising strategies, drug development has stalled in clinical trials. The need for alternative approaches has shifted the spotlight to the 14-3-3 family of proteins, which strongly influence p53 stability and transcriptional activity through direct and indirect interactions. Here, we present the first detailed review of how 14-3-3 proteins regulate p53, with special emphasis on the mechanisms involved in their binding to different members of the pathway. This information will be important to design new compounds that can reactivate p53 in cancer cells by influencing protein-protein interactions. The intricate relationship between the 14-3-3 isoforms and the p53 pathway suggests that many potential drug targets for p53 reactivation could be identified and exploited to design novel antineoplastic therapies with a wide range of applications.

Synergistic effect of ibrutinib and CD19 CAR-T cells on Raji cells in vivo and in vitro

Ibrutinib might improve the efficacy of anti‐CD19 chimeric antigen receptor (CD19 CAR) T‐cell therapy in chronic lymphocytic leukemia (CLL). We studied the possibility and mechanism of the synergistic effect of ibrutinib and CAR‐T cells in other types of lymphoma. In this study, we selected the CD19 CAR‐T cells of a patient with lymphoma who failed in his CD19 CAR‐T‐cell therapy and a dose of 8 mg/kg/d ibrutinib. Subcutaneous and tail vein tumorigenic mice were established with Raji cells. The differences in the synergistic effect between these 2 models were compared by bioluminescence imaging (BLI) monitoring and flow cytometry (FCM). The expression of the STAT‐3 signaling pathway was assessed by western blot analysis. There was no synergistic effect of ibrutinib and CD19 CAR‐T cells in vitro. Programmed cell death‐ligand 1 (PD‐L1) was expressed in 0.23 ± 0.06% of Raji cells. In the subcutaneous tumorigenic model, the luciferase signal was reduced significantly in the group receiving ibrutinib combined with CD19 CAR‐T cells. Moreover, the proportion of CD19 CAR‐T cells was higher in the polytherapy group than in the CAR‐T‐cell monotherapy group. However, we did not get an analogous synergistic effect in the tail vein tumorigenic model. STAT‐3 signaling pathway expression in the residual tumor cells did not differ between those with and those without ibrutinib, suggesting that the IL‐10/STAT‐3/PD‐L1 pathway was not involved in the synergistic effect. Therefore, some other mechanism might be a target for ibrutinib. Our results provide evidence for the use of ibrutinib in polytherapy for other types of B‐cell lymphoma.

14-3-3ζ binds to and stabilizes phospho-beclin 1S295 and induces autophagy in hepatocellular carcinoma cells

Data from The Cancer Genome Atlas (TCGA) indicate that the expression levels of 14‐3‐3ζ and beclin 1 (a key molecule involved in cellular autophagy) are up‐regulated and positively correlated with each other (R = .5, P < .05) in HCC tissues. Chemoresistance developed in hepatoma cancer cells is associated with autophagy initiation. This study aimed to explore 14‐3‐3ζ’s role in regulating autophagy in HCC cells, with a focus on beclin 1. The co‐localization of 14‐3‐3ζ and beclin 1 was detectable in primary HCC tissues. To simulate in vivo tumour microenvironment (hypoxia), CSQT‐2 and HCC‐LM3 cells were exposed to 2% oxygen for 24 hours. The protein levels of 14‐3‐3ζ and phospho‐beclin 1^S295 peaked at 12 hours following hypoxia. Meanwhile, the strongest autophagy flux occurred: LC3II was increased, and p62 was decreased significantly. By sequencing the coding area of BECN 1 gene of CSQT‐2 and HCC‐LM3 cells, we found that the predicted translational products of BECN 1 gene contained RLPS²⁹⁵VP (R, arginine; L, leucine; P, proline; S, serine; V, valine), a classic 14‐3‐3ζ binding motif. CO‐IP results confirmed that 14‐3‐3ζ bound to beclin 1, and this connection was markedly weakened when S²⁹⁵ was mutated into A²⁹⁵ (alanine). Further, 14‐3‐3ζ overexpression prevented phospho‐beclin 1^S295 from degradation and enhanced its binding to VPS34, whilst its knockdown accelerated the degradation. Additionally, 14‐3‐3ζ enhanced the chemoresistance of HCC cells to cis‐diammined dichloridoplatium by activating autophagy. Our work reveals that 14‐3‐3ζ binds to and stabilizes phospho‐beclin 1^S295 and induces autophagy in HCC cells to resist chemotherapy.

14-3-3ζ-A Novel Immunogen Promotes Inflammatory Cytokine Production

The presence of autoantibodies against 14-3-3ζ in human autoimmune diseases indicates its antigenic function. However, neither the cause nor the consequence of this newly-identified antigenic function of 14-3-3ζ protein is known. To address this, we investigated the immunological functions of 14-3-3ζ by studying ex vivo effects on human peripheral blood mononuclear cells (PBMC) proliferation, polarization, and cytokine production. Exogenous 14-3-3ζ promoted PBMC proliferation and T cell polarization toward Th1 and Th17 populations. Significant increases in IFN-γ and IL-17 levels were observed in the presence of 14-3-3ζ. A specific increase in Th1 cells and IFN-γ production provided strong evidence for MHC class II presentation of 14-3-3ζ antigen. Particularly HLA-DRB1^*0401 allele strongly promoted 14-3-3ζ-induced IFN-γ producing cells. In contrast, prednisolone treatment suppressed both 14-3-3ζ-induced T cell polarization and cytokine production. Overall, we show that MHC presentation and the adaptor functions of 14-3-3ζ participate in promoting IFN-γ and IL-17 production, two of the cytokines commonly associated with autoimmune diseases. To the best of our knowledge, this is the first report describing the ex vivo antigenic function of 14-3-3ζ with human PBMC, thereby providing the basis of its immunological role in human diseases.

Noncovalent inhibitors reveal BTK gatekeeper and auto-inhibitory residues that control its transforming activity

Inhibition of Bruton tyrosine kinase (BTK) is a breakthrough therapy for certain B cell lymphomas and B cell chronic lymphatic leukemia. Covalent BTK inhibitors (e.g., ibrutinib) bind to cysteine C481, and mutations of this residue confer clinical resistance. This has led to the development of noncovalent BTK inhibitors that do not require binding to cysteine C481. These new compounds are now entering clinical trials. In a systematic BTK mutagenesis screen, we identify residues that are critical for the activity of noncovalent inhibitors. These include a gatekeeper residue (T474) and mutations in the kinase domain. Strikingly, co-occurrence of gatekeeper and kinase domain lesions (L512M, E513G, F517L, L547P) in cis results in a 10- to 15-fold gain of BTK kinase activity and de novo transforming potential in vitro and in vivo. Computational BTK structure analyses reveal how these lesions disrupt an intramolecular mechanism that attenuates BTK activation. Our findings anticipate clinical resistance mechanisms to a new class of noncovalent BTK inhibitors and reveal intramolecular mechanisms that constrain BTK's transforming potential.

Norepinephrine triggers an immediate-early regulatory network response in primary human white adipocytes

BACKGROUND

Norepinephrine (NE) signaling has a key role in white adipose tissue (WAT) functions, including lipolysis, free fatty acid liberation and, under certain conditions, conversion of white into brite (brown-in-white) adipocytes. However, acute effects of NE stimulation have not been described at the transcriptional network level.

RESULTS

We used RNA-seq to uncover a broad transcriptional response. The inference of protein-protein and protein-DNA interaction networks allowed us to identify a set of immediate-early genes (IEGs) with high betweenness, validating our approach and suggesting a hierarchical control of transcriptional regulation. In addition, we identified a transcriptional regulatory network with IEGs as master regulators, including HSF1 and NFIL3 as novel NE-induced IEG candidates. Moreover, a functional enrichment analysis and gene clustering into functional modules suggest a crosstalk between metabolic, signaling, and immune responses.

CONCLUSIONS

Altogether, our network biology approach explores for the first time the immediate-early systems level response of human adipocytes to acute sympathetic activation, thereby providing a first network basis of early cell fate programs and crosstalks between metabolic and transcriptional networks required for proper WAT function.

14-3-3ζ binds to hepatitis B virus protein X and maintains its protein stability in hepatocellular carcinoma cells

14‐3‐3ζ, a phosphopeptide‐binding molecule, is reportedly overexpressed in the cancerous tissues of patients with hepatocellular carcinoma (HCC). Hepatitis B virus (HBV) protein X (HBx) draws intensive attention in HBV‐related HCC because it not only regulates HBV replication, but also promotes carcinogenesis by interacting with various tumor or antitumor molecules. This study is performed to investigate whether and how 14‐3‐3ζ interacts with HBx. The coimmunoprecipitation (Co‐IP) results showed that 14‐3‐3ζ bond to HBx in HBV‐infected Hep3B HCC cells and CSQT‐2 portal vein tumor thrombosis (PVTT) cells. By performing Co‐IP assay in HBV‐free Huh7 cells expressing wild‐type HBx, mutant HBx‐S31A, or HBx‐S31D (serine³¹ was mutated into alanine³¹ or aspartic acid³¹), we found that the phosphorylated serine³¹ with its near amino acid residues constituted a RPLphosphoS³¹GP (R, arginine; P, proline; L, leucine; S, serine; G, glycine) motif in HBx for 14‐3‐3ζ docking. This 14‐3‐3ζ‐HBx interaction was partly impaired when Akt signaling transduction was blocked by LY294002. Furthermore, 14‐3‐3ζ silencing augmented HBx ubiquitination and decreased its expression in cancer cells and xenograft tumor. The migratory and invasive abilities of CSQT‐2 cells were inhibited upon 14‐3‐3ζ silencing, whereas partly restored by HBx overexpression. Additionally, 14‐3‐3ζ positively correlated with HBx to be overexpressed in the primary HCC tissues (r = 0.344) and metastatic PVTT (r = 0.348). In summary, findings of this study reveal a novel 14‐3‐3ζ‐HBx interaction in HCC cells and suggest 14‐3‐3ζ as a candidate target for treating HBV‐related HCC.

The kinase activity of the channel-kinase protein TRPM7 regulates stability and localization of the TRPM7 channel in polarized epithelial cells

The channel-kinase transient receptor potential melastatin 7 (TRPM7) is a bifunctional protein with ion channel and kinase domains. The kinase activity of TRPM7 has been linked to the regulation of a broad range of cellular activities, but little is understood as to how the channel itself is regulated by its own kinase activity. Here, using several mammalian cell lines expressing WT TRPM7 or kinase-inactive variants, we discovered that compared with the cells expressing WT TRPM7, cells in which TRPM7's kinase activity was inactivated had faster degradation, elevated ubiquitination, and increased intracellular retention of the channel. Mutational analysis of TRPM7 autophosphorylation sites further revealed a role for Ser-1360 of TRPM7 as a key residue mediating both TRPM7 stability and intracellular trafficking. Additional trafficking roles were uncovered for Ser-1403 and Ser-1567, whose phosphorylation by TRPM7's kinase activity mediated the interaction of the channel with the signaling protein 14-3-3θ. In summary, our results point to a critical role for TRPM7's kinase activity in regulating proteasome-mediated turnover of the TRPM7 channel and controlling its cellular localization in polarized epithelial cells. Overall, these findings improve our understanding of the significance of TRPM7's kinase activity for functional regulation of its channel activity.

Pitfalls of Combining Novel Agents in Lymphoma

OPINION STATEMENT

As our knowledge of lymphoma and its intricate signaling pathways has grown, so has the development of novel agents. While their mechanisms of action vary considerably, these therapies supplement and in some cases offer alternatives to standard chemotherapy. Initial studies have highlighted tolerable side effects though in the majority of instances limited efficacy when used as monotherapy. Research has focused on combining these novel agents to improve outcomes and perhaps offer refined treatment options. Novel combinations represent new territory, inherently dissimilar to combination chemotherapy with new pitfalls and challenges given their unique mechanisms of action. Though promising, it is crucial to consider the complex interplay that can occur. While there is potential for improved outcomes, there is also the possibility of unexpected toxicities. For this reason, it is critical that novel combinations be carefully considered and tested in clinical trials before widespread use. Thus far, research has shown that combination therapies are successful when not only avoiding overlapping toxicity but also capitalizing on synergy. We believe that more specific targets and an improved understanding of their off-/on-target effects will further successful novel combinations.

Small-Molecule Stabilization of 14-3-3 Protein-Protein Interactions Stimulates Axon Regeneration

Damaged central nervous system (CNS) neurons have a poor ability to spontaneously regenerate, causing persistent functional deficits after injury. Therapies that stimulate axon growth are needed to repair CNS damage. 14-3-3 adaptors are hub proteins that are attractive targets to manipulate cell signaling. We identify a positive role for 14-3-3s in axon growth and uncover a developmental regulation of the phosphorylation and function of 14-3-3s. We show that fusicoccin-A (FC-A), a small-molecule stabilizer of 14-3-3 protein-protein interactions, stimulates axon growth in vitro and regeneration in vivo. We show that FC-A stabilizes a complex between 14-3-3 and the stress response regulator GCN1, inducing GCN1 turnover and neurite outgrowth. These findings show that 14-3-3 adaptor protein complexes are druggable targets and identify a new class of small molecules that may be further optimized for the repair of CNS damage.

ANKRD54 preferentially selects Bruton's Tyrosine Kinase (BTK) from a Human Src-Homology 3 (SH3) domain library

Bruton's Tyrosine Kinase (BTK) is a cytoplasmic protein tyrosine kinase with a fundamental role in B-lymphocyte development and activation. The nucleocytoplasmic shuttling of BTK is specifically modulated by the Ankyrin Repeat Domain 54 (ANKRD54) protein and the interaction is known to be exclusively SH3-dependent. To identify the spectrum of the ANKRD54 SH3-interactome, we applied phage-display screening of a library containing all the 296 human SH3 domains. The BTK-SH3 domain was the prime interactor. Quantitative western blotting analysis demonstrated the accuracy of the screening procedure. Revealing the spectrum and specificity of ANKRD54-interactome is a critical step toward functional analysis in cells and tissues.

From identification of the BTK kinase to effective management of leukemia

BTK is a cytoplasmic protein-tyrosine kinase, whose corresponding gene was isolated in the early 1990s. BTK was initially identified by positional cloning of the gene causing X-linked agammaglobulinemia and independently in a search for new kinases. Given the phenotype of affected patients, namely lack of B-lymphocytes and plasma cells with the ensuing inability to mount humoral immune responses, BTK inhibitors were anticipated to have beneficial effects on antibody-mediated pathologies, such as autoimmunity. In contrast to, for example, the SRC-family of cytoplasmic kinases, there was no obvious way in which structural alterations would yield constitutively active forms of BTK, and such mutations were also not found in leukemias or lymphomas. In 2007, the first efficient inhibitor, ibrutinib, was reported and soon became approved both in the United States and in Europe for the treatment of three B-cell malignancies, mantle cell lymphoma, chronic lymphocytic leukemia and Waldenström's macroglobulinemia. Over the past few years, additional inhibitors have been developed, with acalabrutinib being more selective, and recently demonstrating fewer clinical adverse effects. The antitumor mechanism is also not related to mutations in BTK. Instead tumor residency in lymphoid organs is inhibited, making these drugs highly versatile. BTK is one of the only 10 human kinases that carry a cysteine in the adenosine triphosphate-binding cleft. As this allows for covalent, irreversible inhibitor binding, it provides these compounds with a highly advantageous character. This quality may be crucial and bodes well for the future of BTK-modifying medicines, which have been estimated to reach annual multi-billion dollar sales in the future.

14-3-3 Proteins regulate K2P 5.1 surface expression on T lymphocytes

K_2P 5.1 channels (also called TASK-2 or Kcnk5) have already been shown to be relevant in the pathophysiology of autoimmune disease because they are known to be upregulated on peripheral and central T lymphocytes of multiple sclerosis (MS) patients. Moreover, overexpression of K_2P 5.1 channels in vitro provokes enhanced T-cell effector functions. However, the molecular mechanisms regulating intracellular K_2P 5.1 channel trafficking are unknown so far. Thus, the aim of the study is to elucidate the trafficking of K_2P 5.1 channels on T lymphocytes. Using mass spectrometry analysis, we have identified 14-3-3 proteins as novel binding partners of K_2P 5.1 channels. We show that a non-classical 14-3-3 consensus motif (R-X-X-pT/S-x) at the channel's C-terminus allows the binding between K_2P 5.1 and 14-3-3. The mutant K_2P 5.1/S266A diminishes the protein-protein interaction and reduces the amplitude of membrane currents. Application of a non-peptidic 14-3-3 inhibitor (BV02) significantly reduces the number of wild-type channels in the plasma membrane, whereas the drug has no effect on the trafficking of the mutated channel. Furthermore, blocker application reduces T-cell effector functions. Taken together, we demonstrate that 14-3-3 interacts with K_2P 5.1 and plays an important role in channel trafficking.

Effects of pholidotaphenanthrene A on proliferation, apoptosis, migration, and cell cycle progression of hepatocellular carcinoma HCCLM3 cells

AIM

To investigate the effects of pholidotaphenanthrene A (PPTA) on the proliferation, apoptosis, migration, and cell cycle progression of hepatocellular carcinoma HCCLM3 cells and the underlying mechanism.

METHODS

Methyl thiazolyl tetrazolium (MTT) assay, flow cytometry and wound healing assay were used to evaluate the effects of PPTA on the viability, cell cycle progression and migration of HCCLM3 cells, respectively. Immunofluorescence staining and Western blot assays were performed to explore the effects of PPTA on F-actin distribution, the formation of lamellipodia and filopodia, and the expression of related signaling molecules.

RESULTS

PPTA decreased the viability of HCCLM3 cells, with IC₅₀ < 50 μmol/L. PPTA at a dose of 40 μmol/L obviously delayed the cell cycle progression of HCCLM3 cells. Results of wound healing assay showed that PPTA can inhibit the relative healing rate of HCCLM3 cells in a dose-dependent manner. Immunofluorescence staining showed that HCCLM3 cells after incubation with different concentrations of PPTA displayed more close arrangement, decreased lamellipodia formation and increased filopodia formation, especially in cells treated with PPTA at a dose of 40 μmol/L. Western blot analysis showed that PPTA at 20 and 40 μmol/L can up-regulate protein kinase B(AKT) and down-regulate pAKT expression.

CONCLUSION

PPTA can inhibit the proliferation, cycle progression, and migration HCCLM3 cells possibly via mechanisms related to altering the levels of pAKT and pERK.

B Cell Receptor Activation Predominantly Regulates AKT-mTORC1/2 Substrates Functionally Related to RNA Processing

Protein kinase B (AKT) phosphorylates numerous substrates on the consensus motif RXRXXpS/T, a docking site for 14-3-3 interactions. To identify novel AKT-induced phosphorylation events following B cell receptor (BCR) activation, we performed proteomics, biochemical and bioinformatics analyses. Phosphorylated consensus motif-specific antibody enrichment, followed by tandem mass spectrometry, identified 446 proteins, containing 186 novel phosphorylation events. Moreover, we found 85 proteins with up regulated phosphorylation, while in 277 it was down regulated following stimulation. Up regulation was mainly in proteins involved in ribosomal and translational regulation, DNA binding and transcription regulation. Conversely, down regulation was preferentially in RNA binding, mRNA splicing and mRNP export proteins. Immunoblotting of two identified RNA regulatory proteins, RBM25 and MEF-2D, confirmed the proteomics data. Consistent with these findings, the AKT-inhibitor (MK-2206) dramatically reduced, while the mTORC-inhibitor PP242 totally blocked phosphorylation on the RXRXXpS/T motif. This demonstrates that this motif, previously suggested as an AKT target sequence, also is a substrate for mTORC1/2. Proteins with PDZ, PH and/or SH3 domains contained the consensus motif, whereas in those with an HMG-box, H15 domains and/or NF-X1-zinc-fingers, the motif was absent. Proteins carrying the consensus motif were found in all eukaryotic clades indicating that they regulate a phylogenetically conserved set of proteins.

Protein kinase B (AKT) regulates SYK activity and shuttling through 14-3-3 and importin 7

The Protein kinase B (AKT) regulates a plethora of intracellular signaling proteins to fine-tune signaling of multiple pathways. Here, we found that following B-cell receptor (BCR)-induced tyrosine phosphorylation of the cytoplasmic tyrosine kinase SYK and the adaptor BLNK, the AKT/PKB enzyme strongly induced BLNK (>100-fold) and SYK (>100-fold) serine/threonine phosphorylation (pS/pT). Increased phosphorylation promoted 14-3-3 binding to BLNK (37-fold) and SYK (2.5-fold) in a pS/pT-concentration dependent manner. We also demonstrated that the AKT inhibitor MK2206 reduced pS/pT of both BLNK (3-fold) and SYK (2.5-fold). Notably, the AKT phosphatase, PHLPP2 maintained the activating phosphorylation of BLNK at Y84 and increased protein stability (8.5-fold). In addition, 14-3-3 was required for the regulation SYK's interaction with BLNK and attenuated SYK binding to Importin 7 (5-fold), thereby perturbing shuttling to the nucleus. Moreover, 14-3-3 proteins also sustained tyrosine phosphorylation of SYK and BLNK. Furthermore, substitution of S295 or S297 for alanine abrogated SYK's binding to Importin 7. SYK with S295A or S297A replacements showed intense pY525/526 phosphorylation, and BLNK pY84 phosphorylation correlated with the SYK pY525/526 phosphorylation level. Conversely, the corresponding mutations to aspartic acid in SYK reduced pY525/526 phosphorylation. Collectively, these and previous results suggest that AKT and 14-3-3 proteins down-regulate the activity of several BCR-associated components, including BTK, BLNK and SYK and also inhibit SYK's interaction with Importin 7.

Targeting B-cell receptor signaling in leukemia and lymphoma: how and why?

B-lymphocytes are dependent on B-cell receptor (BCR) signaling for the constant maintenance of their physiological function, and in many B-cell malignancies this signaling pathway is prone to aberrant activation. This understanding has led to an ever-increasing interest in the signaling networks activated following ligation of the BCR in both normal and malignant cells, and has been critical in establishing an array of small molecule inhibitors targeting BCR-induced signaling. By dissecting how different malignancies signal through BCR, researchers are contributing to the design of more customized therapeutics which have greater efficacy and lower toxicity than previous therapies. This allows clinicians access to an array of approaches to best treat patients whose malignancies have BCR signaling as a driver of pathogenesis.

Substitution scanning identifies a novel, catalytically active ibrutinib-resistant BTK cysteine 481 to threonine (C481T) variant

Irreversible Bruton tyrosine kinase (BTK) inhibitors, ibrutinib and acalabrutinib have demonstrated remarkable clinical responses in multiple B-cell malignancies. Acquired resistance has been identified in a sub-population of patients in which mutations affecting BTK predominantly substitute cysteine 481 in the kinase domain for catalytically active serine, thereby ablating covalent binding of inhibitors. Activating substitutions in the BTK substrate phospholipase Cγ2 (PLCγ2) instead confers resistance independent of BTK. Herein, we generated all six possible amino acid substitutions due to single nucleotide alterations for the cysteine 481 codon, in addition to threonine, requiring two nucleotide substitutions, and performed functional analysis. Replacement by arginine, phenylalanine, tryptophan or tyrosine completely inactivated the catalytic activity, whereas substitution with glycine caused severe impairment. BTK with threonine replacement was catalytically active, similar to substitution with serine. We identify three potential ibrutinib resistance scenarios for cysteine 481 replacement: (1) Serine, being catalytically active and therefore predominating among patients. (2) Threonine, also being catalytically active, but predicted to be scarce, because two nucleotide changes are needed. (3) As BTK variants replaced with other residues are catalytically inactive, they presumably need compensatory mutations, therefore being very scarce. Glycine and tryptophan variants were not yet reported but likely also provide resistance.

B-cell receptor signaling in the pathogenesis of lymphoid malignancies

B-cell receptor (BCR) signaling pathway plays a central role in B-lymphocyte development and initiation of humoral immunity. Recently, BCR signaling pathway has been shown as a major driver in the pathogenesis of B-cell malignancies. As a result, a vast array of BCR-associated kinases has emerged as rational therapeutic targets changing treatment paradigms in B cell malignancies. Based on high efficacy in early-stage clinical trials, there is rapid clinical development of inhibitors targeting BCR signaling pathway. Here, we describe the essential components of BCR signaling, their function in normal and pathogenic signaling and molecular effects of their inhibition in vitro and in vivo.

Splice-correcting oligonucleotides restore BTK function in X-linked agammaglobulinemia model

X-linked agammaglobulinemia (XLA) is an inherited immunodeficiency that results from mutations within the gene encoding Bruton's tyrosine kinase (BTK). Many XLA-associated mutations affect splicing of BTK pre-mRNA and severely impair B cell development. Here, we assessed the potential of antisense, splice-correcting oligonucleotides (SCOs) targeting mutated BTK transcripts for treating XLA. Both the SCO structural design and chemical properties were optimized using 2'-O-methyl, locked nucleic acid, or phosphorodiamidate morpholino backbones. In order to have access to an animal model of XLA, we engineered a transgenic mouse that harbors a BAC with an authentic, mutated, splice-defective human BTK gene. BTK transgenic mice were bred onto a Btk knockout background to avoid interference of the orthologous mouse protein. Using this model, we determined that BTK-specific SCOs are able to correct aberrantly spliced BTK in B lymphocytes, including pro-B cells. Correction of BTK mRNA restored expression of functional protein, as shown both by enhanced lymphocyte survival and reestablished BTK activation upon B cell receptor stimulation. Furthermore, SCO treatment corrected splicing and restored BTK expression in primary cells from patients with XLA. Together, our data demonstrate that SCOs can restore BTK function and that BTK-targeting SCOs have potential as personalized medicine in patients with XLA.

Btk regulates macrophage polarization in response to lipopolysaccharide

Bacterial Lipopolysaccharide (LPS) is a strong inducer of inflammation and does so by inducing polarization of macrophages to the classic inflammatory M1 population. Given the role of Btk as a critical signal transducer downstream of TLR4, we investigated its role in M1/M2 induction. In Btk deficient (Btk^−\−) mice we observed markedly reduced recruitment of M1 macrophages following intraperitoneal administration of LPS. Ex vivo analysis demonstrated an impaired ability of Btk^−/− macrophages to polarize into M1 macrophages, instead showing enhanced induction of immunosuppressive M2-associated markers in response to M1 polarizing stimuli, a finding accompanied by reduced phosphorylation of STAT1 and enhanced STAT6 phosphorylation. In addition to STAT activation, M1 and M2 polarizing signals modulate the expression of inflammatory genes via differential activation of transcription factors and regulatory proteins, including NF-κB and SHIP1. In keeping with a critical role for Btk in macrophage polarization, we observed reduced levels of NF-κB p65 and Akt phosphorylation, as well as reduced induction of the M1 associated marker iNOS in Btk^−/− macrophages in response to M1 polarizing stimuli. Additionally enhanced expression of SHIP1, a key negative regulator of macrophage polarisation, was observed in Btk^−/− macrophages in response to M2 polarizing stimuli. Employing classic models of allergic M2 inflammation, treatment of Btk^−/− mice with either Schistosoma mansoni eggs or chitin resulted in increased recruitment of M2 macrophages and induction of M2-associated genes. This demonstrates an enhanced M2 skew in the absence of Btk, thus promoting the development of allergic inflammation.