Pten regulates spindle pole movement through Dlg1-mediated recruitment of Eg5 to centrosomes

HN1 expression contributes to mitotic fidelity through Aurora A-PLK1-Eg5 axis

Hematological and neurological expressed 1 (HN1) is homolog of Jupiter protein from Drosophila melanogaster where it functions as a microtubule-associated protein. However, in mammalian cells, HN1 is associated partially with y-tubulin in centrosomes, Stathmin for stabilizing microtubules, and Cdh1 for regulating Cyclin B1 for cell cycle regulation. Moreover, HN1 overexpression leads to early mitotic exit as well. Other molecular functions and interactions of HN1 are not clear yet. Here, based on our previous analysis where HN1 was shown to cluster supernumerary centrosomes and maintain mitotic spindle assembly, we further investigated the role of HN1 in centrosome maintenance and mitotic fidelity in PC-3 prostate and MDA-MB231 mammary cancer cell lines. The maturation-associated roles of HN1 during cell division by examining the AuroraA-PLK1 axis involving a plus end kinesin, Eg5 as well as pericentriolar matrix protein (PCM1) as components of centrosomes were established. We found that HN1 co-localized to centrioles with Eg5 and Aurora A to suppress aberrant spindle formation to ensure the fidelity of centriole/centrosome duplication when overexpressed. Consistently, depleting the HN1 expression using siRNA or shRNA resulted in an increased number of dysregulated mitotic spindle structures, where Aurora A as well as PLK1 co-localizations with Eg5 and PCM1 were disrupted. Further, the PLK1 and Aurora A kinase's phosphorylations also decreased, confirming the hypothesis that the cells struggle in mitotic progression, display nuclear and cytokinetic abnormalities with supernumerary but immature mononucleated centrosomes. In summary, we described the role of HN1 in centrosome nucleation/maturation in PLK1-Eg5 axis and concomitant mitotic spindle formation in human cells.

PTEN-Long inhibits the biological behaviors of glioma cells

OBJECTIVES

PTEN-Long is a translational variant of phosphatase and tensin homolog (PTEN). This study aimed to assess the effect of PTEN-Long on the biological characteristics of glioma cells and related mechanisms.

METHODS

A vector stably expressing PTEN-Long was established and transfected into cells, serving as the overexpression group, while a set of empty vectors served as the negative control group. Real-time reverse transcription-polymerase chain reaction (RT-PCR) and western blot were used to detect the expression of PTEN-Long and phosphatidylinositol 3-kinase, Protein kinase B, andnuclear factor-κB (PI3K-AKT-NF-κB). Cell proliferation was assessed with the Cell Counting Kit 8 (CCK8) assay, migration through the scratch test, and invasion by the transwell chamber assay. Cell cycle analysis was performed using flow cytometry. The volume and weight of subcutaneous tumors in nude mice were also evaluated.

RESULTS

PTEN-Long expression led to downregulation of p-Akt, NF-κB p65, p-NF-κB p65, and Bcl-xl, and up-regulation of IκBα. In addition, it inhibited glioma cell proliferation, induced cell cycle arrest in the G0/G1 phase, and reduced cell migration and invasion. Moreover, PTEN-Long inhibited the growth of subcutaneous glioma in nude mice.

CONCLUSIONS

PTEN-Long inhibits the proliferation, migration, and invasion and induces apoptosis in glioma cells by inhibiting PI3K-AKT-NF-κb signaling, implying that PTEN-Long may be a new target for glioma treatment.

DLG1 functions upstream of SDCCAG3 and IFT20 to control ciliary targeting of polycystin-2

Polarized vesicular trafficking directs specific receptors and ion channels to cilia, but the underlying mechanisms are poorly understood. Here we describe a role for DLG1, a core component of the Scribble polarity complex, in regulating ciliary protein trafficking in kidney epithelial cells. Conditional knockout of Dlg1 in mouse kidney causes ciliary elongation and cystogenesis, and cell-based proximity labeling proteomics and fluorescence microscopy show alterations in the ciliary proteome upon loss of DLG1. Specifically, the retromer-associated protein SDCCAG3, IFT20, and polycystin-2 (PC2) are reduced in the cilia of DLG1-deficient cells compared to control cells. This phenotype is recapitulated in vivo and rescuable by re-expression of wild-type DLG1, but not a Congenital Anomalies of the Kidney and Urinary Tract (CAKUT)-associated DLG1 variant, p.T489R. Finally, biochemical approaches and Alpha Fold modelling suggest that SDCCAG3 and IFT20 form a complex that associates, at least indirectly, with DLG1. Our work identifies a key role for DLG1 in regulating ciliary protein composition and suggests that ciliary dysfunction of the p.T489R DLG1 variant may contribute to CAKUT.

The two sides of chromosomal instability: drivers and brakes in cancer

Chromosomal instability (CIN) is a hallmark of cancer and is associated with tumor cell malignancy. CIN triggers a chain reaction in cells leading to chromosomal abnormalities, including deviations from the normal chromosome number or structural changes in chromosomes. CIN arises from errors in DNA replication and chromosome segregation during cell division, leading to the formation of cells with abnormal number and/or structure of chromosomes. Errors in DNA replication result from abnormal replication licensing as well as replication stress, such as double-strand breaks and stalled replication forks; meanwhile, errors in chromosome segregation stem from defects in chromosome segregation machinery, including centrosome amplification, erroneous microtubule-kinetochore attachments, spindle assembly checkpoint, or defective sister chromatids cohesion. In normal cells, CIN is deleterious and is associated with DNA damage, proteotoxic stress, metabolic alteration, cell cycle arrest, and senescence. Paradoxically, despite these negative consequences, CIN is one of the hallmarks of cancer found in over 90% of solid tumors and in blood cancers. Furthermore, CIN could endow tumors with enhanced adaptation capabilities due to increased intratumor heterogeneity, thereby facilitating adaptive resistance to therapies; however, excessive CIN could induce tumor cells death, leading to the "just-right" model for CIN in tumors. Elucidating the complex nature of CIN is crucial for understanding the dynamics of tumorigenesis and for developing effective anti-tumor treatments. This review provides an overview of causes and consequences of CIN, as well as the paradox of CIN, a phenomenon that continues to perplex researchers. Finally, this review explores the potential of CIN-based anti-tumor therapy.

Mitotic Functions and Characters of KIF11 in Cancers

Mitosis mediates the accurate separation of daughter cells, and abnormalities are closely related to cancer progression. KIF11, a member of the kinesin family, plays a vital role in the formation and maintenance of the mitotic spindle. Recently, an increasing quantity of data have demonstrated the upregulated expression of KIF11 in various cancers, promoting the emergence and progression of cancers. This suggests the great potential of KIF11 as a prognostic biomarker and therapeutic target. However, the molecular mechanisms of KIF11 in cancers have not been systematically summarized. Therefore, we first discuss the functions of the protein encoded by KIF11 during mitosis and connect the abnormal expression of KIF11 with its clinical significance. Then, we elucidate the mechanism of KIF11 to promote various hallmarks of cancers. Finally, we provide an overview of KIF11 inhibitors and outline areas for future work.

DLG1 functions upstream of SDCCAG3 and IFT20 to control ciliary targeting of polycystin-2

Polarized vesicular trafficking directs specific receptors and ion channels to cilia, but the underlying mechanisms are poorly understood. Here we describe a role for DLG1, a core component of the Scribble polarity complex, in regulating ciliary protein trafficking in kidney epithelial cells. Conditional knockout of Dlg1 in mouse kidney caused ciliary elongation and cystogenesis, and cell-based proximity labelling proteomics and fluorescence microscopy showed alterations in the ciliary proteome upon loss of DLG1. Specifically, the retromer-associated protein SDCCAG3, IFT20 and polycystin-2 (PC2) were reduced in cilia of DLG1 deficient cells compared to control cells. This phenotype was recapitulated in vivo and rescuable by re-expression of wildtype DLG1, but not a Congenital Anomalies of the Kidney and Urinary Tract (CAKUT)-associated DLG1 variant, p.T489R. Finally, biochemical approaches and Alpha Fold modelling suggested that SDCCAG3 and IFT20 form a complex that associates, at least indirectly, with DLG1. Our work identifies a key role for DLG1 in regulating ciliary protein composition and suggests that ciliary dysfunction of the p.T489R DLG1 variant may contribute to CAKUT.

Hyperphosphorylated PTEN exerts oncogenic properties

PTEN is a multifaceted tumor suppressor that is highly sensitive to alterations in expression or function. The PTEN C-tail domain, which is rich in phosphorylation sites, has been implicated in PTEN stability, localization, catalytic activity, and protein interactions, but its role in tumorigenesis remains unclear. To address this, we utilized several mouse strains with nonlethal C-tail mutations. Mice homozygous for a deletion that includes S370, S380, T382 and T383 contain low PTEN levels and hyperactive AKT but are not tumor prone. Analysis of mice containing nonphosphorylatable or phosphomimetic versions of S380, a residue hyperphosphorylated in human gastric cancers, reveal that PTEN stability and ability to inhibit PI3K-AKT depends on dynamic phosphorylation-dephosphorylation of this residue. While phosphomimetic S380 drives neoplastic growth in prostate by promoting nuclear accumulation of β-catenin, nonphosphorylatable S380 is not tumorigenic. These data suggest that C-tail hyperphosphorylation creates oncogenic PTEN and is a potential target for anti-cancer therapy.

Phospho PTEN mediated dephosphorylation of mitotic kinase PLK1 and Aurora Kinase A prevents aneuploidy and preserves genomic stability

PTEN, dual phosphatase tumor suppressor protein, is found to be frequently mutated in various cancers. Post-translational modification of PTEN is important for its sub-cellular localization and catalytic functions. But how these modifications affect cytological damage and aneuploidy is not studied in detail. We focus on the role of phosphatase activity along with C-terminal phosphorylation of PTEN in perspective of cytological damage like micronucleus, nuclear bud, and nuclear bridge formation. Our data suggest that wild-type PTEN, but not phospho-mutant PTEN significantly reduces cytological damage in PTEN null PC3 cells. In case of phosphatase-dead PTEN, cytological damage markers are increased during 24 h recovery after DNA damage. When we use phosphorylation and phosphatase-dead dual mutant PTEN, the extent of different cytological DNA damage parameters are similar to phosphatase-dead PTEN. We also find that both of those activities are essential for maintaining chromosome numbers. PTEN null cells exhibit significantly aberrant γ-tubulin pole formation during metaphase. Interestingly, we observed that p-PTEN localized to spindle poles along with PLK1 and Aurora Kinase A. Further depletion of phosphorylation and phosphatase activity of PTEN increases the expression of p-Aurora Kinase A (T288) and p-PLK1 (T210), compared to cells expressing wild-type PTEN. Again, wild-type PTEN but not phosphorylation-dead mutant is able to physically interact with PLK1 and Aurora Kinase A. Thus, our study suggests that the phosphorylation-dependent interaction of PTEN with PLK1 and Aurora Kinase A causes dephosphorylation of those mitotic kinases and by lowering their hyperphosphorylation status, PTEN prevents aberrant chromosome segregation in metaphase.

Chromosome instability in neuroblastoma: A pathway to aggressive disease

For over 100-years, genomic instability has been investigated as a central player in the pathogenesis of human cancer. Conceptually, genomic instability includes an array of alterations from small deletions/insertions to whole chromosome alterations, referred to as chromosome instability. Chromosome instability has a paradoxical impact in cancer. In most instances, the introduction of chromosome instability has a negative impact on cellular fitness whereas in cancer it is usually associated with a worse prognosis. One exception is the case of neuroblastoma, the most common solid tumor outside of the brain in children. Neuroblastoma tumors have two distinct patterns of genome instability: whole-chromosome aneuploidy, which is associated with a better prognosis, or segmental chromosomal alterations, which is a potent negative prognostic factor. Through a computational screen, we found that low levels of the de- ubiquitinating enzyme USP24 have a highly significant negative impact on survival in neuroblastoma. At the molecular level, USP24 loss leads to destabilization of the microtubule assembly factor CRMP2 - producing mitotic errors and leading to chromosome missegregation and whole-chromosome aneuploidy. This apparent paradox may be reconciled through a model in which whole chromosome aneuploidy leads to the subsequent development of segmental chromosome alterations. Here we review the mechanisms behind chromosome instability and the evidence for the progressive development of segmental alterations from existing numerical aneuploidy in support of a multi-step model of neuroblastoma progression.

The phosphorylation and dephosphorylation switch of VCP/p97 regulates the architecture of centrosome and spindle

The proper orientation of centrosome and spindle is essential for genome stability; however, the mechanism that governs these processes remains elusive. Here, we demonstrated that polo-like kinase 1 (Plk1), a key mitotic kinase, phosphorylates residue Thr76 in VCP/p97 (an AAA-ATPase), at the centrosome from prophase to anaphase. This phosphorylation process recruits VCP to the centrosome and in this way, it regulates centrosome orientation. VCP exhibits strong co-localization with Eg5 (a mitotic kinesin motor), at the mitotic spindle, and the dephosphorylation of Thr76 in VCP is required for the enrichment of both VCP and Eg5 at the spindle, thus ensuring proper spindle architecture and chromosome segregation. We also showed that the phosphatase, PTEN, is responsible for the dephosphorylation of Thr76 in VCP; when PTEN was knocked down, the normal spread of VCP from the centrosome to the spindle was abolished. Cryo-EM structures of VCPT76A and VCPT76E, which represent dephosphorylated and phosphorylated states of VCP, respectively, revealed that the Thr76 phosphorylation modulates VCP by altering the inter-domain and inter-subunit interactions, and ultimately the nucleotide-binding pocket conformation. Interestingly, the tumor growth in nude mice implanted with VCPT76A-reconstituted cancer cells was significantly slower when compared with those implanted with VCPWT-reconstituted cancer cells. Collectively, our findings demonstrate that the phosphorylation and dephosphorylation switch of VCP regulates the architecture of centrosome and spindle for faithful chromosome segregation.

The Mechanisms of lncRNA-Mediated Multidrug Resistance and the Clinical Application Prospects of lncRNAs in Breast Cancer

Simple Summary

Multidrug resistance (MDR) is a major cause of breast cancer (BC) chemotherapy failure. Long noncoding RNAs (lncRNAs) have been shown closely related to the chemoresistance of BC. In this work, the mechanisms of lncRNA-mediated MDR in BC were elaborated from eight sections, including apoptosis, autophagy, DNA repair, cell cycle, drug efflux, epithelial-mesenchymal transition, epigenetic modification and the tumor microenvironment. Additionally, we also discuss the clinical significance of lncRNAs, which may be biomarkers for diagnosis, therapy and prognosis.

Abstract

Breast cancer (BC) is a highly heterogeneous disease and presents a great threat to female health worldwide. Chemotherapy is one of the predominant strategies for the treatment of BC; however, multidrug resistance (MDR) has seriously affected or hindered the effect of chemotherapy. Recently, a growing number of studies have indicated that lncRNAs play vital and varied roles in BC chemoresistance, including apoptosis, autophagy, DNA repair, cell cycle, drug efflux, epithelial-mesenchymal transition (EMT), epigenetic modification and the tumor microenvironment (TME). Although thousands of lncRNAs have been implicated in the chemoresistance of BC, a systematic review of their regulatory mechanisms remains to be performed. In this review, we systematically summarized the mechanisms of MDR and the functions of lncRNAs mediated in the chemoresistance of BC from the latest literature. These findings significantly enhance the current understanding of lncRNAs and suggest that they may be promising prognostic biomarkers for BC patients receiving chemotherapy, as well as therapeutic targets to prevent or reverse chemoresistance.

NAT10 regulates mitotic cell fate by acetylating Eg5 to control bipolar spindle assembly and chromosome segregation

Cell fate of mitotic cell is controlled by spindle assembly. Deficient spindle assembly results in mitotic catastrophe leading to cell death to maintain cellular homeostasis. Therefore, inducing mitotic catastrophe provides a strategy for tumor therapy. Nucleolar acetyltransferase NAT10 has been found to regulate various cellular processes to maintain cell homeostasis. Here we report that NAT10 regulates mitotic cell fate by acetylating Eg5. NAT10 depletion results in multinuclear giant cells, which is the hallmark of mitotic catastrophe. Live-cell imaging showed that knockdown of NAT10 dramatically prolongs the mitotic time and induces defective chromosome segregation including chromosome misalignment, bridge and lagging. NAT10 binds and co-localizes with Eg5 in the centrosome during mitosis. Depletion of NAT10 reduces the centrosome loading of Eg5 and impairs the poleward movement of centrosome, leading to monopolar and asymmetrical spindle formation. Furthermore, NAT10 stabilizes Eg5 through its acetyltransferase function. NAT10 acetylates Eg5 at K771 to control Eg5 stabilization. We generated K771-Ac specific antibody and showed that Eg5 K771-Ac specifically localizes in the centrosome during mitosis. Additionally, K771 acetylation is required for the motor function of Eg5. The hyper-acetylation mimic Flag-Eg5 K771Q but not Flag-Eg5 rescued the NAT10 depletion-induced defective spindle formation and mitotic catastrophe, demonstrating that NAT10 controls mitosis through acetylating Eg5 K771. Collectively, we identify Eg5 as an important substrate of NAT10 in the control of mitosis and provide K771 as an essential acetylation site in the stabilization and motor function of Eg5. Our findings reveal that targeting the NAT10-mediated Eg5 K771 acetylation provides a potential strategy for tumor therapy.

Non-canonical function of nuclear PTEN and its implication on tumorigenesis

Suppression of genomic instability is the key to prevent tumor development. PTEN is a unique tumor suppressor protein having both lipid and protein phosphatase activities. Interestingly though it is a cytoplasmic protein, but a significant pool of PTEN can also be localized in nucleus. The function of cytoplasmic PTEN is well defined and extensively studied in various literatures focusing mainly on the negative regulation of oncogenic PI-3Kinase-AKT pathway but functional regulation of nuclear PTEN is less defined and therefore it is a fascinating subject of research in cancer biology. Post-translation modulation of PTEN such as phosphorylation, sumorylation, acetylation and methylation also regulates its cellular localization, protein-protein association and catalytic function. Loss or mutation in PTEN is associated with the development of tumors in various tissues from the brain to prostate. Here we have summarized the role of nuclear PTEN and its epigenetic modulation in various DNA metabolic pathways, for example, DNA damage response, DNA repair, DNA replication, DNA segregation etc. Further, pathways involved in nuclear PTEN degradation are also discussed. Additionally, we also emphasize probable potential targets associated with PTEN pathway for chemotherapeutic purpose.

Microtubule motors in centrosome homeostasis: A target for cancer therapy?

Cancer is a grievous concern to human health, owing to a massive heterogeneity in its cause and impact. Dysregulation (numerical, positional and/or structural) of centrosomes is one of the notable factors among those that promote onset and progression of cancers. In a normal dividing cell, a pair of centrosomes forms two poles, thereby governing the formation of a bipolar spindle assembly. A large number of cancer cells, however, harbor supernumerary centrosomes, which mimic the bipolar arrangement in normal cells by centrosome clustering (CC) into two opposite poles, thus developing a pseudo-bipolar spindle assembly. Manipulation of centrosome homeostasis is the paramount pre-requisite for the evasive strategy of CC in cancers. Out of the varied factors that uphold centrosome integrity, microtubule motors (MiMos) play a critical role. Categorized as dyneins and kinesins, MiMos are involved in cohesion of centrosomes, and also facilitate the maintenance of the numerical, positional and structural integrity of centrosomes. Herein, we elucidate the decisive mechanisms undertaken by MiMos to mediate centrosome homeostasis, and how dysregulation of the same might lead to CC in cancer cells. Understanding the impact of MiMos on CC might open up avenues toward a credible therapeutic target against diverse cancers.

FoxM1 insufficiency hyperactivates Ect2-RhoA-mDia1 signaling to drive cancer

FoxM1 activates genes that regulate S-G2-M cell-cycle progression and, when overexpressed, is associated with poor clinical outcome in multiple cancers. Here we identify FoxM1 as a tumor suppressor in mice that, through its N-terminal domain, binds to and inhibits Ect2 to limit the activity of RhoA GTPase and its effector mDia1, a catalyst of cortical actin nucleation. FoxM1 insufficiency impedes centrosome movement through excessive cortical actin polymerization, thereby causing the formation of non-perpendicular mitotic spindles that missegregate chromosomes and drive tumorigenesis in mice. Importantly, low FOXM1 expression correlates with RhoA GTPase hyperactivity in multiple human cancer types, indicating that suppression of the newly discovered Ect2-RhoAmDia1 oncogenic axis by FoxM1 is clinically relevant. Furthermore, by dissecting the domain requirements through which FoxM1 inhibits Ect2 GEF activity, we provide mechanistic insight for the development of pharmacological approaches that target protumorigenic RhoA activity.

Whole-transcriptome sequencing profiling identifies functional and prognostic signatures in patients with PTPRZ1-MET fusion-negative secondary glioblastoma multiforme

Gliomas are the most common type of primary brain tumor in adults with a high mortality rate. Low-grade gliomas progress to glioblastoma multiforme (GBM) in the majority of cases, forming secondary GBM (sGBM), followed by rapid fatal clinical outcomes. Protein tyrosine phosphatase receptor type Z1 (PTPRZ1)-MET proto-oncogene receptor tyrosine kinase (MET) (ZM) fusion has been identified as a biomarker for sGBM that is involved in glioma progression, but the mechanism of gliomagenesis and pathology of ZM-negative sGBM has remained to be fully elucidated. A whole-transcriptome signature is thus required to improve the outcome prediction for patients with sGBM without ZM fusion. In the present study, whole-transcriptome sequencing on 42 sGBM samples with or without ZM fusion from the Chinese Glioma Genome Atlas database identified mRNAs with differential expression between patients with and without ZM fusion and the most significant survival-associated genes were identified. A 6-gene signature was identified as a novel prognostic model reflecting survival probability in patients with ZM-negative sGBM. Clinical characteristics in patients with a high or low risk score value were analyzed with the Kaplan-Meier method and a two-sided log-rank test. In addition, ZM-negative sGBM patients with a high risk score exhibited an increase in immune cells, NF-κB-induced pathway activation and a decrease in endothelial cells compared with those with a low risk score. The present study demonstrated the potential use of a next-generation sequencing-based cancer gene signature in patients with ZM-negative sGBM, indicating possible clinical therapeutic strategies for further treatment of such patients.

PTEN as a Guardian of the Genome: Pathways and Targets

Faithful transmission of genetic information is only possible with the structural and functional integrity of the genome. PTEN has been recognized as a guardian of the genome since the identification of its noncanonical localization and function in the nucleus. Yet, the role of PTEN in guarding the genome relies on integration of diverse mechanisms elicited by its canonical activity in antagonizing PI3K as well as emerging noncanonical functions. In the nucleus, PTEN maintains the structural integrity of chromosomes and the architecture of heterochromatin by physically interacting with chromosomal and nucleosomal components. PTEN also controls the functional integrity of key genetic transmission machineries by promoting proper assembly of the replisome and mitotic spindles. Deregulation of PTEN signaling impairs genome integrity, leading to spontaneous replication/mitotic stress and subsequent stress tolerance. Identification of novel targets of PTEN signaling and illumination of the interplay of diverse PTEN pathways in genome maintenance will help us better understand mechanisms underlying tumor evolution and therapeutic resistance.

BubR1 allelic effects drive phenotypic heterogeneity in mosaic-variegated aneuploidy progeria syndrome

Mosaic-variegated aneuploidy (MVA) syndrome is a rare childhood disorder characterized by biallelic BUBR1, CEP57, or TRIP13 aberrations; increased chromosome missegregation; and a broad spectrum of clinical features, including various cancers, congenital defects, and progeroid pathologies. To investigate the mechanisms underlying this disorder and its phenotypic heterogeneity, we mimicked the BUBR1L1012P mutation in mice (BubR1L1002P) and combined it with 2 other MVA variants, BUBR1X753 and BUBR1H, generating a truncated protein and low amounts of wild-type protein, respectively. Whereas BubR1X753/L1002P and BubR1H/X753 mice died prematurely, BubR1H/L1002P mice were viable and exhibited many MVA features, including cancer predisposition and various progeroid phenotypes, such as short lifespan, dwarfism, lipodystrophy, sarcopenia, and low cardiac stress tolerance. Strikingly, although these mice had a reduction in total BUBR1 and spectrum of MVA phenotypes similar to that of BubR1H/H mice, several progeroid pathologies were attenuated in severity, which in skeletal muscle coincided with reduced senescence-associated secretory phenotype complexity. Additionally, mice carrying monoallelic BubR1 mutations were prone to select MVA-related pathologies later in life, with predisposition to sarcopenia correlating with mTORC1 hyperactivity. Together, these data demonstrate that BUBR1 allelic effects beyond protein level and aneuploidy contribute to disease heterogeneity in both MVA patients and heterozygous carriers of MVA mutations.

MiR-301a Promotes Cell Proliferation by Repressing PTEN in Renal Cell Carcinoma

Objective

Renal cell carcinoma (RCC) displays an increasing incidence and mortality rate worldwide in recent years. More and more evidence demonstrated microRNAs function as positive or negative regulatory factors in many cancers, while the role of miR-301a in RCC is still unclear.

Material and Methods

The expression and clinical significance of miR-301a were assessed via bioinformatic software on open microarray datasets of the Cancer Genome Atlas (TCGA) and then confirmed by quantitative real-time PCR (qRT-PCR) in RCC cell lines. Loss of function assays were performed in RCC cell lines both in vitro and in vivo. Cell Counting Kit-8 (CCK-8), flow cytometry, luciferase reporter assays, Western blotting, and immunohistochemistry were employed to explore the mechanisms of the effect of miR-301a on RCC.

Results

By analyzing RCC clinical specimens and cell lines, we found a uniform increased miR-301a in expression in comparison with normal renal tissue or normal human proximal tubule epithelial cell line (HK-2). In addition, miR-301a upregulation correlated advanced stage and poor prognosis of clear cell RCC (ccRCC). Anti-miR-301a could inhibit growth and cell cycle G1/S transition in RCC cell lines. Moreover, we found that PTEN was identified as a direct target of miR-301a that might partially interrupt miR-301a-induced G1/S transition. Importantly, nude-mouse models revealed that knockdown of miR-301a delayed tumor growth.

Conclusion

These results indicate that miR-301a functions as a tumor-promoting miRNA through regulating PTEN expression, representing a novel therapeutic target for RCC.

Discs large homolog 1 regulates B-cell proliferation and antibody production

Antibody production results from B-cell activation and proliferation upon antigen binding. Discs large homolog 1 (Dlg1), a scaffold protein from the membrane-associated guanylate kinase family, has been shown to regulate the antigen receptor signaling and cell polarity in lymphocytes; however, the physiological function of Dlg1 in humoral responses is not completely clear. Here, we addressed this question using a conditional knockout (KO) mouse model with Dlg1 deficiency in different B-cell subsets by crossing dlg1fl/fl mice with either mb1cre/+ or aicdacre/+ mice, respectively. In both mouse models, we observed that Dlg1 deficiency in B cells (Dlg1-KO B cells) led to obvious hyper-antibody responses upon immunization, the effect of which was more obvious in antigen-recall responses. Mechanistically, we found that Dlg1-KO B cells exhibited hyper-proliferation compared with wild-type B cells upon antigen stimulation, suggesting that the hyper-antibody responses are likely induced by the hyper-proliferation of Dlg1-KO B cells. Indeed, further studies demonstrated that Dlg1 deficiency in B cells led to the down-regulation of a tumor suppressor, FoxO1. Thus, all these results reveal an unexpected function of Dlg1 in restraining hyper-antibody responses through the inhibition of FoxO1 and thus antigen-binding-induced proliferation in B cells.

The Centrosome Linker and Its Role in Cancer and Genetic Disorders

Centrosome cohesion, the joining of the two centrosomes of a cell, is increasingly appreciated as a major regulator of cell functions such as Golgi organization and cilia positioning. One major element of centrosome cohesion is the centrosome linker that consists of a growing number of proteins. The timely disassembly of the centrosome linker enables centrosomes to separate and assemble a functional bipolar mitotic spindle that is crucial for maintaining genomic integrity. Exciting new findings link centrosome linker defects to cell transformation and genetic disorders. We review recent data on the molecular mechanisms of the assembly and disassembly of the centrosome linker, and discuss how defects in the proper execution of these processes cause DNA damage and genomic instability leading to disease.

Kinesin-5 Is Dispensable for Bipolar Spindle Formation and Elongation in Candida albicans, but Simultaneous Loss of Kinesin-14 Activity Is Lethal

Mitotic spindles assume a bipolar architecture through the concerted actions of microtubules, motors, and cross-linking proteins. In most eukaryotes, kinesin-5 motors are essential to this process, and cells will fail to form a bipolar spindle without kinesin-5 activity. Remarkably, inactivation of kinesin-14 motors can rescue this kinesin-5 deficiency by reestablishing the balance of antagonistic forces needed to drive spindle pole separation and spindle assembly. We show that the yeast form of the opportunistic fungus Candida albicans assembles bipolar spindles in the absence of its sole kinesin-5, CaKip1, even though this motor exhibits stereotypical cell-cycle-dependent localization patterns within the mitotic spindle. However, cells lacking CaKip1 function have shorter metaphase spindles and longer and more numerous astral microtubules. They also show defective hyphal development. Interestingly, a small population of CaKip1-deficient spindles break apart and reform two bipolar spindles in a single nucleus. These spindles then separate, dividing the nucleus, and then elongate simultaneously in the mother and bud or across the bud neck, resulting in multinucleate cells. These data suggest that kinesin-5-independent mechanisms drive assembly and elongation of the mitotic spindle in C. albicans and that CaKip1 is important for bipolar spindle integrity. We also found that simultaneous loss of kinesin-5 and kinesin-14 (CaKar3Cik1) activity is lethal. This implies a divergence from the antagonistic force paradigm that has been ascribed to these motors, which could be linked to the high mitotic error rate that C. albicans experiences and often exploits as a generator of diversity.IMPORTANCE Candida albicans is one of the most prevalent fungal pathogens of humans and can infect a broad range of niches within its host. This organism frequently acquires resistance to antifungal agents through rapid generation of genetic diversity, with aneuploidy serving as a particularly important adaptive mechanism. This paper describes an investigation of the sole kinesin-5 in C. albicans, which is a major regulator of chromosome segregation. Contrary to other eukaryotes studied thus far, C. albicans does not require kinesin-5 function for bipolar spindle assembly or spindle elongation. Rather, this motor protein associates with the spindle throughout mitosis to maintain spindle integrity. Furthermore, kinesin-5 loss is synthetically lethal with loss of kinesin-14-canonically an opposing force producer to kinesin-5 in spindle assembly and anaphase. These results suggest a significant evolutionary rewiring of microtubule motor functions in the C. albicans mitotic spindle, which may have implications in the genetic instability of this pathogen.

Multifaceted Regulation of PTEN Subcellular Distributions and Biological Functions

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a tumor suppressor gene frequently found to be inactivated in over 30% of human cancers. PTEN encodes a 54-kDa lipid phosphatase that serves as a gatekeeper of the phosphoinositide 3-kinase pathway involved in the promotion of multiple pro-tumorigenic phenotypes. Although the PTEN protein plays a pivotal role in carcinogenesis, cumulative evidence has implicated it as a key signaling molecule in several other diseases as well, such as diabetes, Alzheimer's disease, and autism spectrum disorders. This finding suggests that diverse cell types, especially differentiated cells, express PTEN. At the cellular level, PTEN is widely distributed in all subcellular compartments and organelles. Surprisingly, the cytoplasmic compartment, not the plasma membrane, is the predominant subcellular location of PTEN. More recently, the finding of a secreted 'long' isoform of PTEN and the presence of PTEN in the cell nucleus further revealed unexpected biological functions of this multifaceted molecule. At the regulatory level, PTEN activity, stability, and subcellular distribution are modulated by a fascinating array of post-translational modification events, including phosphorylation, ubiquitination, and sumoylation. Dysregulation of these regulatory mechanisms has been observed in various human diseases. In this review, we provide an up-to-date overview of the knowledge gained in the last decade on how different functional domains of PTEN regulate its biological functions, with special emphasis on its subcellular distribution. This review also highlights the findings of published studies that have reported how mutational alterations in specific PTEN domains can lead to pathogenesis in humans.

Perspective: Potential Impact and Therapeutic Implications of Oncogenic PI3K Activation on Chromosomal Instability

Genetic activation of the class I PI3K pathway is very common in cancer. This mostly results from oncogenic mutations in PIK3CA, the gene encoding the ubiquitously expressed PI3Kα catalytic subunit, or from inactivation of the PTEN tumour suppressor, a lipid phosphatase that opposes class I PI3K signalling. The clinical impact of PI3K inhibitors in solid tumours, aimed at dampening cancer-cell-intrinsic PI3K activity, has thus far been limited. Challenges include poor drug tolerance, incomplete pathway inhibition and pre-existing or inhibitor-induced resistance. The principle of pharmacologically targeting cancer-cell-intrinsic PI3K activity also assumes that all cancer-promoting effects of PI3K activation are reversible, which might not be the case. Emerging evidence suggests that genetic PI3K pathway activation can induce and/or allow cells to tolerate chromosomal instability, which-even if occurring in a low fraction of the cell population-might help to facilitate and/or drive tumour evolution. While it is clear that such genomic events cannot be reverted pharmacologically, a role for PI3K in the regulation of chromosomal instability could be exploited by using PI3K pathway inhibitors to prevent those genomic events from happening and/or reduce the pace at which they are occurring, thereby dampening cancer development or progression. Such an impact might be most effective in tumours with clonal PI3K activation and achievable at lower drug doses than the maximum-tolerated doses of PI3K inhibitors currently used in the clinic.

Ccne1 Overexpression Causes Chromosome Instability in Liver Cells and Liver Tumor Development in Mice

BACKGROUND & AIMS

The CCNE1 locus, which encodes cyclin E1, is amplified in many types of cancer cells and is activated in hepatocellular carcinomas (HCCs) from patients infected with hepatitis B virus or adeno-associated virus type 2, due to integration of the virus nearby. We investigated cell-cycle and oncogenic effects of cyclin E1 overexpression in tissues of mice.

METHODS

We generated mice with doxycycline-inducible expression of Ccne1 (Ccne1^T mice) and activated overexpression of cyclin E1 from age 3 weeks onward. At 14 months of age, livers were collected from mice that overexpress cyclin E1 and nontransgenic mice (controls) and analyzed for tumor burden and by histology. Mouse embryonic fibroblasts (MEFs) and hepatocytes from Ccne1^T and control mice were analyzed to determine the extent to which cyclin E1 overexpression perturbs S-phase entry, DNA replication, and numbers and structures of chromosomes. Tissues from 4-month-old Ccne1^T and control mice (at that age were free of tumors) were analyzed for chromosome alterations, to investigate the mechanisms by which cyclin E1 predisposes hepatocytes to transformation.

RESULTS

Ccne1^T mice developed more hepatocellular adenomas and HCCs than control mice. Tumors developed only in livers of Ccne1^T mice, despite high levels of cyclin E1 in other tissues. Ccne1^T MEFs had defects that promoted chromosome missegregation and aneuploidy, including incomplete replication of DNA, centrosome amplification, and formation of nonperpendicular mitotic spindles. Whereas Ccne1^T mice accumulated near-diploid aneuploid cells in multiple tissues and organs, polyploidization was observed only in hepatocytes, with losses and gains of whole chromosomes, DNA damage, and oxidative stress.

CONCLUSIONS

Livers, but not other tissues of mice with inducible overexpression of cyclin E1, develop tumors. More hepatocytes from the cyclin E1-overexpressing mice were polyploid than from control mice, and had losses or gains of whole chromosomes, DNA damage, and oxidative stress; all of these have been observed in human HCC cells. The increased risk of HCC in patients with hepatitis B virus or adeno-associated virus type 2 infection might involve activation of cyclin E1 and its effects on chromosomes and genomes of liver cells.

The balance of forces generated by kinesins controls spindle polarity and chromosomal heterogeneity in tetraploid cells

Chromosomal instability, one of the most prominent features of tumour cells, causes aneuploidy. Tetraploidy is thought to be an intermediate on the path to aneuploidy, but the mechanistic relationship between the two states is poorly understood. Here, we show that spindle polarity (e.g., bipolarity or multipolarity) in tetraploid cells depends on the level of functional phospho-Eg5, a mitotic kinesin, localised at the spindle. Multipolar spindles are formed in cells with high levels of phospho-Eg5. This process is suppressed by inhibition of Eg5 or expression of a non-phosphorylatable Eg5 mutant, as well as by changing the balance between opposing forces required for centrosome separation. Tetraploid cells with high levels of functional Eg5 give rise to a heterogeneous aneuploid population via multipolar division, whereas those with low levels of functional Eg5 continue to undergo bipolar division and remain tetraploid. Furthermore, Eg5 expression levels correlate with ploidy status in tumour specimens. We provide a novel explanation for the tetraploid intermediate model: spindle polarity and subsequent tetraploid cell behaviour are determined by the balance of forces generated by mitotic kinesins at the spindle.

Mitotic live-cell imaging at different timescales

Mitosis is a highly dynamic and choreographed process in which chromosomes are captured by the mitotic spindle and physically segregated into the two daughter cells to ensure faithful transmission of the genetic material. Live-cell fluorescence microscopy enables these dynamics to be analyzed over diverse temporal scales. Here we present the methodologies to study chromosome segregation at three timescales: we first show how automated tracking of kinetochores enables investigation of mitotic spindle and chromosome dynamics in the seconds-to-minutes timescale; next we highlight how new DNA live dyes allow the study of chromosome segregation over a period of several hours in any cell line; finally, we demonstrate how image sequences acquired over several days can reveal the fate of whole cell populations over several consecutive cell divisions.

Myeloid Disease Mutations of Splicing Factor SRSF2 Cause G2-M Arrest and Skewed Differentiation of Human Hematopoietic Stem and Progenitor Cells

Myeloid malignancies, including myelodysplastic syndromes, chronic myelomonocytic leukemia, and acute myeloid leukemia, are characterized by abnormal proliferation and differentiation of hematopoietic stem and progenitor cells (HSPCs). Reports on analysis of bone marrow samples from patients have revealed a high incidence of mutations in splicing factors in early stem and progenitor cell clones, but the mechanisms underlying transformation of HSPCs harboring these mutations remain unknown. Using ex vivo cultures of primary human CD34⁺ cells as a model, we find that mutations in splicing factors SRSF2 and U2AF1 exert distinct effects on proliferation and differentiation of HSPCs. SRSF2 mutations cause a dramatic inhibition of proliferation via a G2-M phase arrest and induction of apoptosis. U2AF1 mutations, conversely, do not significantly affect proliferation. Mutations in both SRSF2 and U2AF1 cause abnormal differentiation by skewing granulo-monocytic differentiation toward monocytes but elicit diverse effects on megakaryo-erythroid differentiation. The SRSF2 mutations skew differentiation toward megakaryocytes whereas U2AF1 mutations cause an increase in the erythroid cell populations. These distinct functional consequences indicate that SRSF2 and U2AF1 mutations have cell context-specific effects and that the generation of myeloid disease phenotype by mutations in the genes coding these two proteins likely involves different intracellular mechanisms. Stem Cells 2018;36:1663-1675.

Mosaic-variegated aneuploidy syndrome mutation or haploinsufficiency in Cep57 impairs tumor suppression

A homozygous truncating frameshift mutation in CEP57 (CEP57T/T) has been identified in a subset of mosaic-variegated aneuploidy (MVA) patients; however, the physiological roles of the centrosome-associated protein CEP57 that contribute to disease are unknown. To investigate these, we have generated a mouse model mimicking this disease mutation. Cep57T/T mice died within 24 hours after birth with short, curly tails and severely impaired vertebral ossification. Osteoblasts in lumbosacral vertebrae of Cep57T/T mice were deficient for Fgf2, a Cep57 binding partner implicated in diverse biological processes, including bone formation. Furthermore, a broad spectrum of tissues of Cep57T/T mice had severe aneuploidy at birth, consistent with the MVA patient phenotype. Cep57T/T mouse embryonic fibroblasts and patient-derived skin fibroblasts failed to undergo centrosome maturation in G2 phase, causing premature centriole disjunction, centrosome amplification, aberrant spindle formation, and high rates of chromosome missegregation. Mice heterozygous for the truncating frameshift mutation or a Cep57-null allele were overtly indistinguishable from WT mice despite reduced Cep57 protein levels, yet prone to aneuploidization and cancer, with tumors lacking evidence for loss of heterozygosity. This study identifies Cep57 as a haploinsufficient tumor suppressor with biologically diverse roles in centrosome maturation and Fgf2-mediated bone formation.

Non-canonical functions of the mitotic kinesin Eg5

Kinesins are widely expressed, microtubule-dependent motors that play vital roles in microtubule-associated cellular activities, such as cell division and intracellular transport. Eg5, also known as kinesin-5 or kinesin spindle protein, is a member of the kinesin family that contributes to the formation and maintenance of the bipolar mitotic spindle during cell division. Small-molecule compounds that inhibit Eg5 activity have been shown to impair spindle assembly, block mitotic progression, and possess anti-cancer activity. Recent studies focusing on the localization and functions of Eg5 in plants have demonstrated that in addition to spindle organization, this motor protein has non-canonical functions, such as chromosome segregation and cytokinesis, that have not been observed in animals. In this review, we discuss the structure, function, and localization of Eg5 in various organisms, highlighting the specific role of this protein in plants. We also propose directions for the future studies of novel Eg5 functions based on the lessons learned from plants.

The impact of mitotic errors on cell proliferation and tumorigenesis

This review by Levine and Holland reviews the sources of mitotic errors in human tumors and their effect on cell fitness and transformation. They discuss new findings that suggest that chromosome missegregation can produce a proinflammatory environment and impact tumor responsiveness to immunotherapy and survey the vulnerabilities exposed by cell division errors and how they can be exploited therapeutically.

Mitosis is a delicate event that must be executed with high fidelity to ensure genomic stability. Recent work has provided insight into how mitotic errors shape cancer genomes by driving both numerical and structural alterations in chromosomes that contribute to tumor initiation and progression. Here, we review the sources of mitotic errors in human tumors and their effect on cell fitness and transformation. We discuss new findings that suggest that chromosome missegregation can produce a proinflammatory environment and impact tumor responsiveness to immunotherapy. Finally, we survey the vulnerabilities exposed by cell division errors and how they can be exploited therapeutically.

The Phosphatase PTPL1 Is Required for PTEN-Mediated Regulation of Apical Membrane Size

PTEN is a tumor suppressor that is frequently lost in epithelial malignancies. A part of the tumor-suppressive properties of PTEN is attributed to its function in cell polarization and consequently its role in maintaining epithelial tissue integrity. However, surprisingly little is known about the function and regulation of PTEN during epithelial cell polarization. We used clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9-mediated gene disruption to delete PTEN in intestinal epithelial Ls174T:W4 cells, which upon differentiation form a microvillus-covered apical membrane (brush border) on a part of the cell cortex, independent of cell-cell junctions. We show that loss of PTEN results in the formation of a larger brush border that, in a fraction of the cells, even spans the entire plasma membrane, revealing that PTEN functions in the regulation of apical membrane size. Depletion of the phosphatase PTPL1 resulted in a similar defect. PTPL1 interacts with PTEN, and this interaction is necessary for apical membrane enrichment of PTEN. Importantly, phosphatase activity of PTPL1 is not required, indicating that PTPL1 functions as an anchor protein in this process. Our work thus demonstrates a novel function for PTEN during cell polarization in controlling apical membrane size and identifies PTPL1 as a critical apical membrane anchor for PTEN in this process.

PTEN PDZ-binding domain suppresses mammary carcinogenesis in the MMTV-PyMT breast cancer model

Phosphatase and tension homolog (PTEN) is a potent tumor suppressor that possesses a PDZ-binding domain (PDZ-BD) at the end of its carboxyl terminus, whose functions during tumorigenesis remains unclear. Here, we crossed a mouse strain with germline deletion of PTEN PDZ-BD with MMTV-PyMT breast cancer model, and found that knockout (KO) mice display normal development of mammary glands, but have both increased breast tumorigenicity and lung metastasis. Orthotopic allograft experiments suggest the loss of PTEN PDZ-BD in breast cancer cells rather than in tumor microenvironment plays a prominent role in increasing tumor burden. Through RNA-sequencing, we observed a significant downregulation of myoepithelial marker genes in both KO primary breast cancer and orthotopic allografts. Moreover, these myoepithelial marker genes are significantly downregulated in human breast cancer tissues, and are associated with poorer clinical prognosis. In addition, several homeobox genes were also identified to be downreguated in KO breast cancer, whose expressions showed significant positive correlation with myoepithelial marker genes. Overall, our findings suggest a novel tumor suppressive role of PTEN PDZ-BD in a murine model of breast cancer, and the mechanism involves the dysregulation of homeobox genes which may result in defective myoepithelial differentiation in breast cancer cells.

Once and only once: mechanisms of centriole duplication and their deregulation in disease

Centrioles are conserved microtubule-based organelles that form the core of the centrosome and act as templates for the formation of cilia and flagella. Centrioles have important roles in most microtubule-related processes, including motility, cell division and cell signalling. To coordinate these diverse cellular processes, centriole number must be tightly controlled. In cycling cells, one new centriole is formed next to each pre-existing centriole in every cell cycle. Advances in imaging, proteomics, structural biology and genome editing have revealed new insights into centriole biogenesis, how centriole numbers are controlled and how alterations in these processes contribute to diseases such as cancer and neurodevelopmental disorders. Moreover, recent work has uncovered the existence of surveillance pathways that limit the proliferation of cells with numerical centriole aberrations. Owing to this progress, we now have a better understanding of the molecular mechanisms governing centriole biogenesis, opening up new possibilities for targeting these pathways in the context of human disease.

Identification of a PTEN mutation with reduced protein stability, phosphatase activity, and nuclear localization in Hong Kong patients with autistic features, neurodevelopmental delays, and macrocephaly

PTEN is a tumor suppressor gene inactivated in over 30% of human cancers. It encodes a lipid phosphatase that serves as a gatekeeper of the phosphoinositide 3-kinase signaling pathway. Germline mutation frequently occurs in this gene in patients diagnosed with PTEN Hamartoma Tumor Syndrome (PHTS). PHTS individuals are characterized by macrocephaly, benign growth of multiple tissues and increased tumor risk. In addition, autistic phenotypes are found in 10-20% of individuals carrying the germline PTEN mutation with macrocephaly. In this report, 13 suspected PHTS patients were screened for mutation in the PTEN gene. A missense variant (c. 302T > C) substituting the isoleucine at codon 101 to a threonine, a single nucleotide insertion (c. 327-328insC) causing a frame shift mutation and termination at codon 109, and a nonsense variant (c. 1003C > T) truncated the protein at codon 335 were identified. The I101T mutation significantly reduced PTEN protein expression levels by 2.5- to 4.0-fold. Mechanistically, I101T reduced the protein half-life of PTEN possibly due to enhanced polyubiquitination at Lysine 13. However, the I101T mutant retained almost 30% of the lipid phosphatase activity of the wild-type protein. Finally, the I101T mutant has reduced phosphorylation at a PTEN auto-dephosphorylation site at Threonine 366 and a lowered ratio of nuclear to cytosolic protein level. These partial losses of multiple PTEN biochemical functions may contribute to the tissue overgrowth and autistic features of this PHTS patient. Autism Res 2018, 11: 1098-1109. © 2018 The Authors Autism Research published by International Society for Autism Research and Wiley Periodicals, Inc. LAY SUMMARY: The genetics of autism spectrum disorders is highly complex with individual risk influenced by both genetic and environmental factors. Mutation in the human PTEN gene confers a high risk of developing autistic behavior. This report revealed that PTEN mutations occurred in 23% of a selected group of Hong Kong patients harboring autistic features with gross overgrowth symptoms. Detailed characterization of a PTEN mutation revealed reduced protein stability as one of the underlying mechanisms responsible for reduced PTEN activity.

Differential gene expression induced by anti-cancer agent plumbagin is mediated by androgen receptor in prostate cancer cells

Treatment of mice harboring PTEN-P2 tumors in the prostate or on prostate tissue in vivo with 5-hydroxy-2-methyl-1,4-naphthoquinone, also known as plumbagin, results in tumor regression in castrated mice, but not in intact mice. This suggested that dihydrotestosterone (DHT) production in the testes may prevent cell death due to plumbagin treatment, but the underlying mechanism is not understood. We performed RNA-seq analysis on cells treated with combinations of plumbagin and DHT, and analyzed differential gene expression, to gain insight into the interactions between androgen and plumbgin. DHT and plumbagin synergize to alter the expression of many genes that are not differentially regulated by either single agent when used alone. These experiments revealed that, for many genes, increases in mRNAs caused by DHT are sharply down-regulated by plumbagin, and that many transcripts change in response to plumbagin in a DHT-dependent manner. This suggests that androgen receptor mediates some of the effects of plumbagin on gene expression.

Interference of HTLV-1 Tax Protein with Cell Polarity Regulators: Defining the Subcellular Localization of the Tax-DLG1 Interaction

Human T cell leukemia virus (HTLV)-1 Tax (Tax) protein is very important in viral replication and cell transformation. Tax localizes in the nucleus and cytoplasm in association with organelles. Some activities of Tax depend on interactions with PDZ (PSD-95/Discs Large/Z0-1) domain-containing proteins such as Discs large protein 1 (DLG1) which is involved in cell polarity and proliferation. The DLG1 interaction results in a cytoplasmic co-localization pattern resembling vesicular aggregates, the nature of which is still unknown. To further explore the role of PDZ proteins in HTLV-1 cell transformation, we deeply investigated the Tax-DLG1 association. By fluorescence resonance energy transfer (FRET), we detected, for the first time, the direct binding of Tax to DLG1 within the cell. We showed that the interaction specifically affects the cellular distribution of not only DLG1, but also Tax. After studying different cell structures, we demonstrated that the aggregates distribute into the Golgi apparatus in spatial association with the microtubule-organizing center (MTOC). This study contributes to understand the biological significance of Tax-PDZ interactions.

PTEN Regulates Glucose Transporter Recycling by Impairing SNX27 Retromer Assembly

The tumor suppressor PTEN executes cellular functions predominantly through its phosphatase activity. Here we identified a phosphatase-independent role for PTEN during vesicular trafficking of the glucose transporter GLUT1. PTEN physically interacts with SNX27, a component of the retromer complex that recycles transmembrane receptors such as GLUT1 from endosomes to the plasma membrane. PTEN binding with SNX27 prevents GLUT1 accumulation at the plasma membrane because of defective recycling and thus reduces cellular glucose uptake. Mechanistically, PTEN blocks the association of SNX27 with VPS26 and thereby hinders assembly of a functional retromer complex during the receptor recycling process. Importantly, we found a PTEN somatic mutation (T401I) that is defective in disrupting the association between SNX27 and VPS26, suggesting a critical role for PTEN in controlling optimal GLUT1 levels at the membrane to prevent tumor progression. Together, our results reveal a fundamental role of PTEN in the regulation of the SNX27 retromer pathway, which governs glucose transport and might contribute to PTEN tumor suppressor function.

PTEN in the maintenance of genome integrity: From DNA replication to chromosome segregation

Faithful DNA replication and accurate chromosome segregation are the key machineries of genetic transmission. Disruption of these processes represents a hallmark of cancer and often results from loss of tumor suppressors. PTEN is an important tumor suppressor that is frequently mutated or deleted in human cancer. Loss of PTEN has been associated with aneuploidy and poor prognosis in cancer patients. In mice, Pten deletion or mutation drives genomic instability and tumor development. PTEN deficiency induces DNA replication stress, confers stress tolerance, and disrupts mitotic spindle architecture, leading to accumulation of structural and numerical chromosome instability. Therefore, PTEN guards the genome by controlling multiple processes of chromosome inheritance. Here, we summarize current understanding of the PTEN function in promoting high-fidelity transmission of genetic information. We also discuss the PTEN pathways of genome maintenance and highlight potential targets for cancer treatment.

Src family kinase phosphorylation of the motor domain of the human kinesin-5, Eg5

Spindle formation in mammalian cells requires precise spatial and temporal regulation of the kinesin-5, Eg5, which generates outward force to establish spindle bipolarity. Our results demonstrate that Eg5 is phosphorylated in cultured cells by Src family kinases (SFKs) at three sites in the motor head: Y125, Y211, and Y231. Mutation of these sites diminishes motor activity in vitro, and replacement of endogenous Eg5 with phosphomimetic Y211 in LLC-Pk1 cells results in monopolar spindles, consistent with loss of Eg5 activity. Cells treated with SFK inhibitors show defects in spindle formation, similar to those in cells expressing the nonphosphorylatable Y211 mutant, and distinct from inhibition of other mitotic kinases. We propose that this phosphoregulatory mechanism tunes Eg5 enzymatic activity for optimal spindle morphology.

Cell Cycle Control by PTEN

Continuous and error-free chromosome inheritance through the cell cycle is essential for genomic stability and tumor suppression. However, accumulation of aberrant genetic materials often causes the cell cycle to go awry, leading to malignant transformation. In response to genotoxic stress, cells employ diverse adaptive mechanisms to halt or exit the cell cycle temporarily or permanently. The intrinsic machinery of cycling, resting, and exiting shapes the cellular response to extrinsic stimuli, whereas prevalent disruption of the cell cycle machinery in tumor cells often confers resistance to anticancer therapy. Phosphatase and tensin homolog (PTEN) is a tumor suppressor and a guardian of the genome that is frequently mutated or deleted in human cancer. Moreover, it is increasingly evident that PTEN deficiency disrupts the fundamental processes of genetic transmission. Cells lacking PTEN exhibit cell cycle deregulation and cell fate reprogramming. Here, we review the role of PTEN in regulating the key processes in and out of cell cycle to optimize genomic integrity.

Cyclin A2 is an RNA binding protein that controls Mre11 mRNA translation

Cyclin A2 activates the cyclin-dependent kinases Cdk1 and Cdk2 and is expressed at elevated levels from S phase until early mitosis. We found that mutant mice that cannot elevate cyclin A2 are chromosomally unstable and tumor-prone. Underlying the chromosomal instability is a failure to up-regulate the meiotic recombination 11 (Mre11) nuclease in S phase, which leads to impaired resolution of stalled replication forks, insufficient repair of double-stranded DNA breaks, and improper segregation of sister chromosomes. Unexpectedly, cyclin A2 controlled Mre11 abundance through a C-terminal RNA binding domain that selectively and directly binds Mre11 transcripts to mediate polysome loading and translation. These data reveal cyclin A2 as a mechanistically diverse regulator of DNA replication combining multifaceted kinase-dependent functions with a kinase-independent, RNA binding-dependent role that ensures adequate repair of common replication errors.

PTEN at the interface of immune tolerance and tumor suppression

BACKGROUND

PTEN is well known to function as a tumor suppressor that antagonizes oncogenic signaling and maintains genomic stability. The PTEN gene is frequently deleted or mutated in human cancers and the wide cancer spectrum associated with PTEN deficiency has been recapitulated in a variety of mouse models of Pten deletion or mutation. Pten mutations are highly penetrant in causing various types of spontaneous tumors that often exhibit resistance to anticancer therapies including immunotherapy. Recent studies demonstrate that PTEN also regulates immune functionality.

OBJECTIVE

To understand the multifaceted functions of PTEN as both a tumor suppressor and an immune regulator.

METHODS

This review will summarize the emerging knowledge of PTEN function in cancer immunoediting. In addition, the mechanisms underlying functional integration of various PTEN pathways in regulating cancer evolution and tumor immunity will be highlighted.

RESULTS

Recent preclinical and clinical studies revealed the essential role of PTEN in maintaining immune homeostasis, which significantly expands the repertoire of PTEN functions. Mechanistically, aberrant PTEN signaling alters the interplay between the immune system and tumors, leading to immunosuppression and tumor escape.

CONCLUSION

Rational design of personalized anti-cancer treatment requires mechanistic understanding of diverse PTEN signaling pathways in modulation of the crosstalk between tumor and immune cells.

PTEN: Local and Global Modulation of Neuronal Function in Health and Disease

Phosphatase and tensin homolog deleted on chromosome ten (PTEN) was recently revealed to be a synaptic player during plasticity events in addition to its well-established role as a general controlling factor in cell proliferation and neuronal growth during development. Alterations of these direct actions of PTEN at synapses may lead to synaptic dysfunction with behavioral and cognitive consequences. A recent paradigmatic example of this situation, Alzheimer's disease (AD), is associated with excessive recruitment of PTEN into synapses leading to pathological synaptic depression. By contrast, some forms of autism are characterized by failure to weaken synaptic connections, which may be related to insufficient PTEN signaling. Understanding the modulation of synaptic function by PTEN in these pathologies may contribute to the development of new therapies.