Master Transcription Factor Reprogramming Unleashes Selective Translation Promoting Castration Resistance and Immune Evasion in Lethal Prostate Cancer.

Signaling rewiring allows tumors to survive therapy. Here we show that the decrease of the master regulator microphthalmia transcription factor (MITF) in lethal prostate cancer unleashes eukaryotic initiation factor 3B (eIF3B)-dependent translation reprogramming of key mRNAs conferring resistance to androgen deprivation therapy (ADT) and promoting immune evasion. Mechanistically, MITF represses through direct promoter binding eIF3B, which in turn regulates the translation of specific mRNAs. Genome-wide eIF3B enhanced cross-linking immunoprecipitation sequencing (eCLIP-seq) showed specialized binding to a UC-rich motif present in subsets of 5' untranslated regions. Indeed, translation of the androgen receptor and major histocompatibility complex I (MHC-I) through this motif is sensitive to eIF3B amount. Notably, pharmacologic targeting of eIF3B-dependent translation in preclinical models sensitizes prostate cancer to ADT and anti-PD-1 therapy. These findings uncover a hidden connection between transcriptional and translational rewiring promoting therapy-refractory lethal prostate cancer and provide a druggable mechanism that may transcend into effective combined therapeutic strategies. SIGNIFICANCE: Our study shows that specialized eIF3B-dependent translation of specific mRNAs released upon downregulation of the master transcription factor MITF confers castration resistance and immune evasion in lethal prostate cancer. Pharmacologic targeting of this mechanism delays castration resistance and increases immune-checkpoint efficacy. This article is featured in Selected Articles from This Issue, p. 2489.

CDK4: a master regulator of the cell cycle and its role in cancer.

The cell cycle is regulated in part by cyclins and their associated serine/threonine cyclin-dependent kinases, or CDKs. CDK4, in conjunction with the D-type cyclins, mediates progression through the G1 phase when the cell prepares to initiate DNA synthesis. Although Cdk4-null mutant mice are viable and cell proliferation is not significantly affected in vitro due to compensatory roles played by other CDKs, this gene plays a key role in mammalian development and cancer. This review discusses the role that CDK4 plays in cell cycle control, normal development and tumorigenesis as well as the current status and utility of approved small molecule CDK4/6 inhibitors that are currently being used as cancer therapeutics.

TGFß reprograms TNF stimulation of macrophages towards a non-canonical pathway driving inflammatory osteoclastogenesis.

It is well-established that receptor activator of NF-κB ligand (RANKL) is the inducer of physiological osteoclast differentiation. However, the specific drivers and mechanisms driving inflammatory osteoclast differentiation under pathological conditions remain obscure. This is especially true given that inflammatory cytokines such as tumor necrosis factor (TNF) demonstrate little to no ability to directly drive osteoclast differentiation. Here, we found that transforming growth factor ß (TGFß) priming enables TNF to effectively induce osteoclastogenesis, independently of the canonical RANKL pathway. Lack of TGFß signaling in macrophages suppresses inflammatory, but not basal, osteoclastogenesis and bone resorption in vivo. Mechanistically, TGFß priming reprograms the macrophage response to TNF by remodeling chromatin accessibility and histone modifications, and enables TNF to induce a previously unrecognized non-canonical osteoclastogenic program, which includes suppression of the TNF-induced IRF1-IFNß-IFN-stimulated-gene axis, IRF8 degradation and B-Myb induction. These mechanisms are active in rheumatoid arthritis, in which TGFß level is elevated and correlates with osteoclast activity. Our findings identify a TGFß/TNF-driven inflammatory osteoclastogenic program, and may lead to development of selective treatments for inflammatory osteolysis.

Posiphen Reduces the Levels of Huntingtin Protein through Translation Suppression.

Posiphen tartrate (Posiphen) is an orally available small molecule that targets a conserved regulatory element in the mRNAs of amyloid precursor protein (APP) and α-synuclein (αSYN) and inhibits their translation. APP and αSYN can cause neurodegeneration when their aggregates induce neurotoxicity. Therefore, Posiphen is a promising drug candidate for neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. Posiphen's safety has been demonstrated in three independent phase I clinical trials. Moreover, in a proof of concept study, Posiphen lowered neurotoxic proteins and inflammatory markers in cerebrospinal fluid of mild cognitive impaired patients. Herein we investigated whether Posiphen reduced the expression of other proteins, as assessed by stable isotope labeling with amino acids in cell culture (SILAC) followed by mass spectrometry (MS)-based proteomics. Neuroblastoma SH-SY5Y cells, an in vitro model of neuronal function, were used for the SILAC protein profiling response. Proteins whose expression was altered by Posiphen treatment were characterized for biological functions, pathways and networks analysis. The most significantly affected pathway was the Huntington's disease signaling pathway, which, along with huntingtin (HTT) protein, was down-regulated by Posiphen in the SH-SY5Y cells. The downregulation of HTT protein by Posiphen was confirmed by quantitative Western blotting and immunofluorescence. Unchanged mRNA levels of HTT and a comparable decay rate of HTT proteins after Posiphen treatment supported the coclusion that Posiphen reduced HTT via downregulation of the translation of HTT mRNA. Meanwhile, the downregulation of APP and αSYN proteins by Posiphen was also confirmed. The mRNAs encoding HTT, APP and αSYN contain an atypical iron response element (IRE) in their 5'-untranslated regions (5'-UTRs) that bind iron regulatory protein 1 (IRP1), and Posiphen specifically bound this complex. Conversely, Posiphen did not bind the IRP1/IRE complex of mRNAs with canonical IREs, and the translation of these mRNAs was not affected by Posiphen. Taken together, Posiphen shows high affinity binding to the IRE/IRP1 complex of mRNAs with an atypical IRE stem loop, inducing their translation suppression, including the mRNAs of neurotoxic proteins APP, αSYN and HTT.

Simultaneous CK2/TNIK/DYRK1 inhibition by 108600 suppresses triple negative breast cancer stem cells and chemotherapy-resistant disease.

Triple negative breast cancer (TNBC) remains challenging because of heterogeneous responses to chemotherapy. Incomplete response is associated with a greater risk of metastatic progression. Therefore, treatments that target chemotherapy-resistant TNBC and enhance chemosensitivity would improve outcomes for these high-risk patients. Breast cancer stem cell-like cells (BCSCs) have been proposed to represent a chemotherapy-resistant subpopulation responsible for tumor initiation, progression and metastases. Targeting this population could lead to improved TNBC disease control. Here, we describe a novel multi-kinase inhibitor, 108600, that targets the TNBC BCSC population. 108600 treatment suppresses growth, colony and mammosphere forming capacity of BCSCs and induces G2M arrest and apoptosis of TNBC cells. In vivo, 108600 treatment of mice bearing triple negative tumors results in the induction of apoptosis and overcomes chemotherapy resistance. Finally, treatment with 108600 and chemotherapy suppresses growth of pre-established TNBC metastases, providing additional support for the clinical translation of this agent to clinical trials.

Novel induction of CD40 expression by tumor cells with RAS/RAF/PI3K pathway inhibition augments response to checkpoint blockade.

BACKGROUND: While immune checkpoint blockade (ICB) is the current first-line treatment for metastatic melanoma, it is effective for ~ 52% of patients and has dangerous side effects. The objective here was to identify the feasibility and mechanism of RAS/RAF/PI3K pathway inhibition in melanoma to sensitize tumors to ICB therapy. METHODS: Rigosertib (RGS) is a non-ATP-competitive small molecule RAS mimetic. RGS monotherapy or in combination therapy with ICB were investigated using immunocompetent mouse models of BRAFwt and BRAFmut melanoma and analyzed in reference to patient data. RESULTS: RGS treatment (300 mg/kg) was well tolerated in mice and resulted in ~ 50% inhibition of tumor growth as monotherapy and ~ 70% inhibition in combination with αPD1 + αCTLA4. RGS-induced tumor growth inhibition depends on CD40 upregulation in melanoma cells followed by immunogenic cell death, leading to enriched dendritic cells and activated T cells in the tumor microenvironment. The RGS-initiated tumor suppression was partially reversed by either knockdown of CD40 expression in melanoma cells or depletion of CD8+ cytotoxic T cells. Treatment with either dabrafenib and trametinib or with RGS, increased CD40+SOX10+ melanoma cells in the tumors of melanoma patients and patient-derived xenografts. High CD40 expression level correlates with beneficial T-cell responses and better survival in a TCGA dataset from melanoma patients. Expression of CD40 by melanoma cells is associated with therapeutic response to RAF/MEK inhibition and ICB. CONCLUSIONS: Our data support the therapeutic use of RGS + αPD1 + αCTLA4 in RAS/RAF/PI3K pathway-activated melanomas and point to the need for clinical trials of RGS + ICB for melanoma patients who do not respond to ICB alone. TRIAL REGISTRATION: NCT01205815 (Sept 17, 2010).

A Contaminant Impurity, Not Rigosertib, Is a Tubulin Binding Agent.

Rigosertib is a styryl benzyl sulfone that inhibits growth of tumor cells and acts as a RAS mimetic by binding to Ras binding domains of RAS effectors. A recent study attributed rigosertib's mechanism of action to microtubule binding. In that study, rigosertib was obtained from a commercial vendor. We compared the purity of clinical-grade and commercially sourced rigosertib and found that commercially sourced rigosertib contains approximately 5% ON01500, a potent inhibitor of tubulin polymerization. Clinical-grade rigosertib, which is free of this impurity, does not exhibit tubulin-binding activity. Cell lines expressing mutant ß-tubulin have also been reported to be resistant to rigosertib. However, our study showed that these cells failed to proliferate in the presence of rigosertib at concentrations that are lethal to wild-type cells. Rigosertib induced a senescence-like phenotype in the small percentage of surviving cells, which could be incorrectly scored as resistant using short-term cultures.

Nuclear Pores Promote Lethal Prostate Cancer by Increasing POM121-Driven E2F1, MYC, and AR Nuclear Import.

Nuclear pore complexes (NPCs) regulate nuclear-cytoplasmic transport, transcription, and genome integrity in eukaryotic cells. However, their functional roles in cancer remain poorly understood. We interrogated the evolutionary transcriptomic landscape of NPC components, nucleoporins (Nups), from primary to advanced metastatic human prostate cancer (PC). Focused loss-of-function genetic screen of top-upregulated Nups in aggressive PC models identified POM121 as a key contributor to PC aggressiveness. Mechanistically, POM121 promoted PC progression by enhancing importin-dependent nuclear transport of key oncogenic (E2F1, MYC) and PC-specific (AR-GATA2) transcription factors, uncovering a pharmacologically targetable axis that, when inhibited, decreased tumor growth, restored standard therapy efficacy, and improved survival in patient-derived pre-clinical models. Our studies molecularly establish a role of NPCs in PC progression and give a rationale for NPC-regulated nuclear import targeting as a therapeutic strategy for lethal PC. These findings may have implications for understanding how NPC deregulation contributes to the pathogenesis of other tumor types.

Targeting protein kinase CK2 and CDK4/6 pathways with a multi-kinase inhibitor ON108110 suppresses pro-survival signaling and growth in mantle cell lymphoma and T-acute lymphoblastic leukemia.

Overexpression and constitutive activation of CYCLIN D1 and Casein Kinase 2 are common features of many hematologic malignancies, including mantle cell lymphoma (MCL) and leukemias such as T-cell acute lymphoblastic leukemia (T-ALL). Although both CK2 and CDK4 inhibitors have shown promising results against these tumor types, none of these agents have achieved objective responses in the clinic as monotherapies. Because both proteins play key roles in these and other hematological malignancies, we have analyzed the therapeutic potential of ON108110, a novel dual specificity ATP-competitive inhibitor of protein kinase CK2 as well as CDK4/6 in MCL and T-ALL. We show that in cell growth inhibition assays, MCL and T-ALL cell lines exhibited increased sensitivity to ON108110 when compared to other tumor types. Treatment with ON108110 reduced the level of phosphorylated RB-family proteins. In addition, ON108110 treatment resulted in concentration dependent inhibition of PTEN phosphorylation and a concomitant decrease in PI3K-AKT signaling mediated by CK2. Accordingly, cells treated with ON108110 rapidly accumulated in the G0/G1 stage of the cell cycle as a function of increasing concentration followed by rapid onset of apoptosis. Together, these results indicate that dual inhibition of CK2 and CDK4/6 may be an efficient treatment of MCL and T-ALLs displaying upregulation of CK2/PI3K and CDK4 signaling pathways.

JNK-signaling: A multiplexing hub in programmed cell death.

Jun N-terminal kinases or JNKs have been shown to be involved in a wide array of signaling events underlying tumorigenesis and tumor progression. Through its interaction with a diverse set of signaling proteins and adaptors, JNKs regulate cell proliferation, invasive migration, therapy resistance, and programmed cell death. JNKs have been shown to play a role in apoptotic as well as non-apoptotic programmed cell death mechanisms including those of necroptosis, ferroptosis, pyroptosis, and autophagy. Most of the tumorigenic regulatory functions of JNKs can be related to their ability to module cell death via these programmed cell death mechanisms. JNKs stimulate or inhibit cell death in a context-dependent manner by stimulating the expression of specific genes as well as by modulating the activities of pro- and anti-apoptotic proteins through distinct phosphorylation events. This review summarizes our current understanding of the role of JNK in programmed cell death and its impact on cancer growth, progression, and therapy.

Drugging the 'undruggable' cancer targets.

The term 'undruggable' was coined to describe proteins that could not be targeted pharmacologically. However, progress is being made to 'drug' many of these targets, and therefore more appropriate terms might be 'difficult to drug' or 'yet to be drugged'. Many desirable targets in cancer fall into this category, including the RAS and MYC oncogenes, and pharmacologically targeting these intractable proteins is now a key challenge in cancer research that requires innovation and the development of new technologies. In this Viewpoint article, we asked four scientists working in this field for their opinions on the most crucial advances, as well as the challenges and what the future holds for this important area of research.

Stage-Specific Human Induced Pluripotent Stem Cells Map the Progression of Myeloid Transformation to Transplantable Leukemia.

Myeloid malignancy is increasingly viewed as a disease spectrum, comprising hematopoietic disorders that extend across a phenotypic continuum ranging from clonal hematopoiesis to myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). In this study, we derived a collection of induced pluripotent stem cell (iPSC) lines capturing a range of disease stages encompassing preleukemia, low-risk MDS, high-risk MDS, and secondary AML. Upon their differentiation, we found hematopoietic phenotypes of graded severity and/or stage specificity that together delineate a phenotypic roadmap of disease progression culminating in serially transplantable leukemia. We also show that disease stage transitions, both reversal and progression, can be modeled in this system using genetic correction or introduction of mutations via CRISPR/Cas9 and that this iPSC-based approach can be used to uncover disease-stage-specific responses to drugs. Our study therefore provides insight into the cellular events demarcating the initiation and progression of myeloid transformation and a new platform for testing genetic and pharmacological interventions.

Aberrant expression of JNK-associated leucine-zipper protein, JLP, promotes accelerated growth of ovarian cancer.

Ovarian cancer is the most fatal gynecologic cancer with poor prognosis. Etiological factors underlying ovarian cancer genesis and progression are poorly understood. Previously, we have shown that JNK-associated Leucine zipper Protein (JLP), promotes oncogenic signaling. Investigating the role of JLP in ovarian cancer, our present study indicates that JLP is overexpressed in ovarian cancer tissue and ovarian cancer cells. Transient overexpression of JLP promotes proliferation and invasive migration of ovarian cancer cells. In addition, ectopic expression of JLP confers long-term survival and clonogenic potential to normal fallopian tube-derived epithelial cells. Coimmunoprecipitation and colocalization analyses demonstrate the in vivo interaction of JLP and JNK, which is stimulated by lysophosphatidic acid (LPA), an oncogenic lipid growth factor in ovarian cancer. We also show that LPA stimulates the translocation of JLP-JNK complex to the perinuclear region of SKOV3-ip cells. JLP-knockdown using shRNA abrogates LPA-stimulated activation of JNK as well as LPA-stimulated proliferation and invasive migration of SKOV3-ip cells. Studies using ovarian cancer xenograft mouse model indicate that the mice bearing JLP-silenced xenografts exhibits reduced tumor volume. Analysis of the xenograft tumor tissues indicate a reduction in the levels of JLP, JNK, phosphorylated-JNK, c-Jun and phosphorylated-c-Jun in JLP-silenced xenografts, thereby correlating the attenuated JLP-JNK signaling node with suppressed tumor growth. Thus, our results identify a critical role for JLP-signaling axis in ovarian cancer and provide evidence that targeting this signaling node could provide a new avenue for therapy.

Angiomotin stabilization by tankyrase inhibitors antagonizes constitutive TEAD-dependent transcription and proliferation of human tumor cells with Hippo pathway core component mutations.

The evolutionarily conserved Hippo inhibitory pathway plays critical roles in tissue homeostasis and organ size control, while mutations affecting certain core components contribute to tumorigenesis. Here we demonstrate that proliferation of Hippo pathway mutant human tumor cells exhibiting high constitutive TEAD transcriptional activity was markedly inhibited by dominant negative TEAD4, which did not inhibit the growth of Hippo wild-type cells with low levels of regulatable TEAD-mediated transcription. The tankyrase inhibitor, XAV939, identified in a screen for inhibitors of TEAD transcriptional activity, phenocopied these effects independently of its other known functions by stabilizing angiomotin and sequestering YAP in the cytosol. We also identified one intrinsically XAV939 resistant Hippo mutant tumor line exhibiting lower and less durable angiomotin stabilization. Thus, angiomotin stabilization provides a new mechanism for targeting tumors with mutations in Hippo pathway core components as well as a biomarker for sensitivity to such therapy.

A Small Molecule RAS-Mimetic Disrupts RAS Association with Effector Proteins to Block Signaling.

Oncogenic activation of RAS genes via point mutations occurs in 20%-30% of human cancers. The development of effective RAS inhibitors has been challenging, necessitating new approaches to inhibit this oncogenic protein. Functional studies have shown that the switch region of RAS interacts with a large number of effector proteins containing a common RAS-binding domain (RBD). Because RBD-mediated interactions are essential for RAS signaling, blocking RBD association with small molecules constitutes an attractive therapeutic approach. Here, we present evidence that rigosertib, a styryl-benzyl sulfone, acts as a RAS-mimetic and interacts with the RBDs of RAF kinases, resulting in their inability to bind to RAS, disruption of RAF activation, and inhibition of the RAS-RAF-MEK pathway. We also find that ribosertib binds to the RBDs of Ral-GDS and PI3Ks. These results suggest that targeting of RBDs across multiple signaling pathways by rigosertib may represent an effective strategy for inactivation of RAS signaling.

Dual Targeting of CDK4 and ARK5 Using a Novel Kinase Inhibitor ON123300 Exerts Potent Anticancer Activity against Multiple Myeloma.

Multiple myeloma is a fatal plasma cell neoplasm accounting for over 10,000 deaths in the United States each year. Despite new therapies, multiple myeloma remains incurable, and patients ultimately develop drug resistance and succumb to the disease. The response to selective CDK4/6 inhibitors has been modest in multiple myeloma, potentially because of incomplete targeting of other critical myeloma oncogenic kinases. As a substantial number of multiple myeloma cell lines and primary samples were found to express AMPK-related protein kinase 5(ARK5), a member of the AMPK family associated with tumor growth and invasion, we examined whether dual inhibition of CDK4 and ARK5 kinases using ON123300 results in a better therapeutic outcome. Treatment of multiple myeloma cell lines and primary samples with ON123300 in vitro resulted in rapid induction of cell-cycle arrest followed by apoptosis. ON123300-mediated ARK5 inhibition or ARK5-specific siRNAs resulted in the inhibition of the mTOR/S6K pathway and upregulation of the AMPK kinase cascade. AMPK upregulation resulted in increased SIRT1 levels and destabilization of steady-state MYC protein. Furthermore, ON123300 was very effective in inhibiting tumor growth in mouse xenograft assays. In addition, multiple myeloma cells sensitive to ON123300 were found to have a unique genomic signature that can guide the clinical development of ON123300. Our study provides preclinical evidence that ON123300 is unique in simultaneously inhibiting key oncogenic pathways in multiple myeloma and supports further development of ARK5 inhibition as a therapeutic approach in multiple myeloma.

Discovery of 2-(1H-indol-5-ylamino)-6-(2,4-difluorophenylsulfonyl)-8-methylpyrido[2,3-d]pyrimidin-7(8H)-one (7ao) as a potent selective inhibitor of Polo like kinase 2 (PLK2).

Several families of protein kinases have been shown to play a critical role in the regulation of cell cycle progression, particularly progression through mitosis. These kinase families include the Aurora kinases, the Mps1 gene product and the Polo Like family of protein kinases (PLKs). The PLK family consists of five members and of these, the role of PLK1 in human cancer is well documented. PLK2 (SNK), which is highly homologous to PLK1, has been shown to play a critical role in centriole duplication and is also believed to play a regulatory role in the survival pathway by physically stabilizing the TSC1/2 complex in tumor cells under hypoxic conditions. As a part of our research program, we have developed a library of novel ATP mimetic chemotypes that are cytotoxic against a panel of cancer cell lines. We show that one of these chemotypes, the 6-arylsulfonyl pyridopyrimidinones, induces apoptosis of human tumor cell lines in nanomolar concentrations. The most potent of these compounds, 7ao, was found to be a highly specific inhibitor of PLK2 when profiled against a panel of 288 wild type, 55 mutant and 12 lipid kinases. Here, we describe the synthesis, structure activity relationship, in vitro kinase specificity and biological activity of the lead compound, 7ao.

Dual inhibition of CDK4/Rb and PI3K/AKT/mTOR pathways by ON123300 induces synthetic lethality in mantle cell lymphomas.

This study describes the characterization of a novel kinase inhibitor, ON123300, which inhibits CDK4/6 (cyclin-dependent kinases 4 and 6) and phosphatidylinositol 3 kinase-δ (PI3K-δ) and exhibits potent activity against mantle cell lymphomas (MCLs) both in vitro and in vivo. We examined the effects of PD0332991 and ON123300 on cell cycle progression, modulation of the retinoblastoma (Rb) and PI3K/AKT pathways, and the induction of apoptosis in MCL cell lines and patient-derived samples. When Granta 519 and Z138C cells were incubated with PD0332991 and ON123300, both compounds were equally efficient in their ability to inhibit the phosphorylation of Rb family proteins. However, only ON123300 inhibited the phosphorylation of proteins associated with the PI3K/AKT pathway. Cells treated with PD0332991 rapidly accumulated in the G0/G1 phase of cell cycle as a function of increasing concentration. Although ON123300-treated cells arrested similarly at lower concentrations, higher concentrations resulted in the induction of apoptosis, which was not observed in PD0332991-treated samples. Mouse xenograft assays also showed a strong inhibition of MCL tumor growth in ON123300-treated animals. Finally, treatment of ibrutinib-sensitive and -resistant patient-derived MCLs with ON123300 also triggered apoptosis and inhibition of the Rb and PI3K/AKT pathways, suggesting that this compound might be an effective agent in MCL, including ibrutinib-resistant forms of the disease.

JNK-associated Leucine Zipper Protein Functions as a Docking Platform for Polo-like Kinase 1 and Regulation of the Associating Transcription Factor Forkhead Box Protein K1.

JLP (JNK-associated leucine zipper protein) is a scaffolding protein that interacts with various signaling proteins associated with coordinated regulation of cellular process such as endocytosis, motility, neurite outgrowth, cell proliferation, and apoptosis. Here we identified PLK1 (Polo-like kinase 1) as a novel interaction partner of JLP through mass spectrometric approaches. Our results indicate that JLP is phospho-primed by PLK1 on Thr-351, which is recognized by the Polo box domain of PLK1 leading to phosphorylation of JLP at additional sites. Stable isotope labeling by amino acids in cell culture and quantitative LC-MS/MS analysis was performed to identify PLK1-dependent JLP-interacting proteins. Treatment of cells with the PLK1 kinase inhibitor BI2536 suppressed binding of the Forkhead box protein K1 (FOXK1) transcriptional repressor to JLP. JLP was found to interact with PLK1 and FOXK1 during mitosis. Moreover, knockdown of PLK1 affected the interaction between JLP and FOXK1. FOXK1 is a known transcriptional repressor of the CDK inhibitor p21/WAF1, and knockdown of JLP resulted in increased FOXK1 protein levels and a reduction of p21 transcript levels. Our results suggest a novel mechanism by which FOXK1 protein levels and activity are regulated by associating with JLP and PLK1.

Identification and characterization of a cell division-regulating kinase AKB1 (associated kinase of Trypanosoma brucei 14-3-3) through proteomics study of the Tb14-3-3 binding proteins.

We used a proteomics approach to identify the binding partners of Trypanosoma brucei 14-3-3 (Tb14-3-3) which led to the identification of a novel kinase, AKB1. The binding between these two proteins was mediated by an amphipathic groove structure in Tb14-3-3 and 1-438 amino acid sequence of AKB1. Recombinant AKB1 but not its ATP-binding-deficient mutant (DFG to NFG) possessed an auto-phosphorylation activity as well as a kinase activity towards a peptide substrate in vitro. However, the autophosphorylation was not required for the binding of AKB1 to Tb14-3-3. Interestingly, the kinase activity of AKB1 was inhibited by calcium, and the kinase was found to utilize GTP, and dATP in addition to ATP as phospho-donors. AKB1 formed homodimers through a leucine-zipper structure. Either knockdown of AKB1 or overexpression of AKB1, but not kinase-dead AKB1 mutant, deregulated cytokinesis and cell division, suggesting that kinase activity of AKB1 is crucial for its function. Furthermore, we showed that AKB1 exists in a detergent insoluble fraction. Laser confocal microscopy revealed that the majority of AKB1 is co-localized with α-tubulin. Taken together, these findings suggest that AKB1 might regulate cytokinesis and cell division by phosphorylating cytoskeleton-associated proteins.