S6K1 is involved in polyploidization through its phosphorylation at Thr421/Ser424

Capivasertib combines with docetaxel to enhance anti-tumour activity through inhibition of AKT-mediated survival mechanisms in prostate cancer

BACKGROUND/OBJECTIVE

To explore the anti-tumour activity of combining AKT inhibition and docetaxel in PTEN protein null and WT prostate tumours.

METHODS

Mechanisms associated with docetaxel capivasertib treatment activity in prostate cancer were examined using a panel of in vivo tumour models and cell lines.

RESULTS

Combining docetaxel and capivasertib had increased activity in PTEN null and WT prostate tumour models in vivo. In vitro short-term docetaxel treatment caused cell cycle arrest in the majority of cells. However, a sub-population of docetaxel-persister cells did not undergo G2/M arrest but upregulated phosphorylation of PI3K/AKT pathway effectors GSK3β, p70S6K, 4E-BP1, but to a lesser extent AKT. In vivo acute docetaxel treatment induced p70S6K and 4E-BP1 phosphorylation. Treating PTEN null and WT docetaxel-persister cells with capivasertib reduced PI3K/AKT pathway activation and cell cycle progression. In vitro and in vivo it reduced proliferation and increased apoptosis or DNA damage though effects were more marked in PTEN null cells. Docetaxel-persister cells were partly reliant on GSK3β as a GSK3β inhibitor AZD2858 reversed capivasertib-induced apoptosis and DNA damage.

CONCLUSION

Capivasertib can enhance anti-tumour effects of docetaxel by targeting residual docetaxel-persister cells, independent of PTEN status, to induce apoptosis and DNA damage in part through GSK3β.

Aryl Hydrocarbon Receptor: From Homeostasis to Tumor Progression

Transcription factor aryl hydrocarbon receptor (AHR) has emerged as one of the main regulators involved both in different homeostatic cell functions and tumor progression. Being a member of the family of basic-helix-loop-helix (bHLH) transcriptional regulators, this intracellular receptor has become a key member in differentiation, pluripotency, chromatin dynamics and cell reprogramming processes, with plenty of new targets identified in the last decade. Besides this role in tissue homeostasis, one enthralling feature of AHR is its capacity of acting as an oncogene or tumor suppressor depending on the specific organ, tissue and cell type. Together with its well-known modulation of cell adhesion and migration in a cell-type specific manner in epithelial-mesenchymal transition (EMT), this duality has also contributed to the arise of its clinical interest, highlighting a new potential as therapeutic tool, diagnosis and prognosis marker. Therefore, a deregulation of AHR-controlled pathways may have a causal role in contributing to physiological and homeostatic failures, tumor progression and dissemination. With that firmly in mind, this review will address the remarkable capability of AHR to exert a different function influenced by the phenotype of the target cell and its potential consequences.

The role of autophagy in escaping therapy-induced polyploidy/senescence

Autophagy is an evolutionarily conserved process necessary to maintain cell homeostasis in response to various forms of stress such as nutrient deprivation and hypoxia as well as functioning to remove damaged molecules and organelles. The role of autophagy in cancer varies depending on the stage of cancer. Cancer therapeutics can also simultaneously evoke cancer cell senescence and ploidy increase. Both cancer cell senescence and polyploidization are reversible by depolyploidization giving rise to the progeny. Autophagy activation may be indispensable for cancer cell escape from senescence/polyploidy. As cancer cell polyploidy is proposed to be involved in cancer origin, the role of autophagy in polyploidization/depolyploidization of senescent cancer cells seems to be crucial. Accordingly, this review is an attempt to understand the complicated interrelationships between reversible cell senescence/polyploidy and autophagy.

Aryl Hydrocarbon Receptor Promotes Liver Polyploidization and Inhibits PI3K, ERK, and Wnt/β-Catenin Signaling

Aryl hydrocarbon receptor (AhR) deficiency alters tissue homeostasis. However, how AhR regulates organ maturation and differentiation remains mostly unknown. Liver differentiation entails a polyploidization process fundamental for cell growth, metabolism, and stress responses. Here, we report that AhR regulates polyploidization during the preweaning-to-adult mouse liver maturation. Preweaning AhR-null (AhR−/−) livers had smaller hepatocytes, hypercellularity, altered cell cycle regulation, and enhanced proliferation. Those phenotypes persisted in adult AhR−/− mice and correlated with compromised polyploidy, predominance of diploid hepatocytes, and enlarged centrosomes. Phosphatidylinositol-3-phosphate kinase (PI3K), extracellular signal-regulated kinase (ERK), and Wnt/β-catenin signaling remained upregulated from preweaning to adult AhR-null liver, likely increasing mammalian target of rapamycin (mTOR) activation. Metabolomics revealed the deregulation of mitochondrial oxidative phosphorylation intermediates succinate and fumarate in AhR−/− liver. Consistently, PI3K, ERK, and Wnt/β-catenin inhibition partially rescued polyploidy in AhR−/− mice. Thus, AhR may integrate survival, proliferation, and metabolism for liver polyploidization. Since tumor cells tend to be polyploid, AhR modulation could have therapeutic value in the liver.

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AhR is required for liver polyploidization during preweaning-to-adult transition

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INS-R/PI3K/AKT, ERK, Wnt/β-Cat and mTOR are downregulated during liver polyploidization

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Reduced polyploidy relates with enhanced mitochondrial metabolism in AhR-null liver

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Understanding how AhR modulates polyploidy may provide strategies against cancer

PLK1 regulates spindle association of phosphorylated eukaryotic translation initiation factor 4E-binding protein and spindle function in mouse oocytes

Oocyte meiotic spindles are associated with spindle-enriched mRNAs, phosphorylated ribosome protein S6, and phosphorylated variants of the key translational regulator, eukaryotic translation initiation factor 4E-binding protein 1 (eIF4E-BP1), consistent with translational control of localized mRNAs by eIF4E-BP1 in facilitating spindle formation and stability. Using specific kinase inhibitors, we determined which kinases regulate phosphorylation status of eIF4E-BP1 associated with meiotic spindles in mouse oocytes and effects of kinase inhibition on chromosome congression and spindle formation. Neither ataxia telangiectasia-mutated kinase nor mechanistic target of rapamycin inhibition significantly affected phosphorylation status of spindle-associated eIF4E-BP1 at the phosphorylation sites examined. Spindle-associated phospho-eIF4E-BP1, spindle formation, and chromosome congression were strongly disrupted by polo-like kinase I (PLK1) inhibition at both metaphase I (MI) and MII. In addition, direct inhibition of eIF4E-BP1 via 4EGI led to spindle defects at MI, indicating a direct role for eIF4E-BP1 phosphorylation in meiotic spindle formation. PLK1 also regulated microtubule dynamics throughout the ooplasm, indicating likely coordination between spindle dynamics and broader ooplasm cytoskeletal dynamics. Because diverse upstream signaling pathways converge on PLK1, these results implicate PLK1 as a major regulatory nexus coupling endogenous and exogenous signals via eIF4E-BP1 to the regulation of spindle formation and stability.

Effects of vascular endothelial growth factors and their receptors on megakaryocytes and platelets and related diseases

It is well known that vascular endothelial growth factors (VEGFs) and their receptors (vascular endothelial growth factor receptors, VEGFRs) are expressed in different tissues, and VEGF-VEGFR loops regulate a wide range of responses, including metabolic homeostasis, cell proliferation, migration and tubuleogenesis. As ligands, VEGFs act on three structurally related VEGFRs (VEGFR1, VEGFR2 and VEGFR3 [also termed FLT1, KDR and FLT4, respectively]) that deliver downstream signals. Haematopoietic stem cells (HSCs), megakaryocytic cell lines, cultured megakaryocytes (MKs), primary MKs and abnormal MKs express and secrete VEGFs. During the development from HSCs to MKs, VEGFR1, VEGFR2 and VEGFR3 are expressed at different developmental stages, respectively, and re-expressed, e.g., VEGFR2, and play different roles in commitment, differentiation, proliferation, survival and polyplodization of HSCs/MKs via autocrine, paracrine and/or even intracrine loops. Moreover, VEGFs and their receptors are abnormally expressed in MK-related diseases, including myeloproliferative neoplasms, myelodysplastic syndromes and acute megakaryocytic leukaemia (a rare subtype of acute myeloid leukaemia), and they lead to the disordered proliferation/differentiation of bone marrow cells and angiogenesis, indicating that they are closely related to these diseases. Thus, targeting VEGF-VEGFR loops may be of potential therapeutic value.

Polyploidy Formation in Doxorubicin-Treated Cancer Cells Can Favor Escape from Senescence

Cancer cells can undergo stress-induced premature senescence, which is considered to be a desirable outcome of anticancer treatment. However, the escape from senescence and cancer cell repopulation give rise to some doubts concerning the effectiveness of the senescence-induced anticancer therapy. Similarly, it is postulated that polyploidization of cancer cells is connected with disease relapse. We postulate that cancer cell polyploidization associated with senescence is the culprit of atypical cell divisions leading to cancer cell regrowth. Accordingly, we aimed to dissociate between these two phenomena. We induced senescence in HCT 116 cells by pulse treatment with doxorubicin and observed transiently increased ploidy, abnormal nuclear morphology, and various distributions of some proteins (e.g., p21, Ki-67, SA-β-galactosidase) in the subnuclei. Doxorubicin-treated HCT 116 cells displayed an increased production of reactive oxygen species (ROS) possibly caused by an increased amount of mitochondria, which are characterized by low membrane potential. A decrease in the level of ROS by Trolox partially protected the cells from polyploidization but not from senescence. Interestingly, a decreased level of ROS prevented the cells from escaping senescence. We also show that MCF7 cells senesce, but this is not accompanied by the increase of ploidy upon doxorubicin treatment. Moreover, they were stably growth arrested, thus proving that polyploidy but not senescence per se enables to regain the ability to proliferate. Our preliminary results indicate that the different propensity of the HCT 116 and MCF7 cells to increase ploidy upon cell senescence could be caused by a different level of the mTOR and/or Pim-1 kinases.

Phosphorylation of ribosomal protein S6 kinase 1 at Thr421/Ser424 and dephosphorylation at Thr389 regulates SP600125-induced polyploidization of megakaryocytic cell lines

Megakaryocytes (MKs) are one of the few cell types that become polyploid; however, the mechanisms by which these cells are designated to become polyploid are not fully understood. In this investigation, we successfully established two relatively synchronous polyploid cell models by inducing Dami and CMK cells with SP600125. We found that SP600125 induced the polyploidization of Dami and CMK cells, concomitant with the phosphorylation of ribosomal protein S6 kinase 1 (S6K1) at Thr421/Ser424 and dephosphorylation at Thr389. The polyploidization was partially blocked by H-89, a cAMP-dependent protein kinase (PKA) inhibitor, through direct binding to S6K1, leading to dephosphorylation at Thr421/Ser424 and phosphorylation at Thr389, independent of PKA. Overexpression of a rapamycin-resistant mutant of S6K1 further enhanced the inhibitory effect of LY294002 on the SP600125-induced polyploidization of Dami and CMK cells. SP600125 also induced the polyploidization of Meg-01 cells, which are derived from a patient with chronic myelogenous leukemia, without causing a significant change in S6K1 phosphorylation. Additionally, SP600125 induced the polyploidization of HEL cells, which are derived from a patient with erythroleukemia, and phosphorylation at Thr389 of S6K1 was detected. However, the polyploidization of both Meg-01 cells and HEL cells as a result of SP600125 treatment was lower than that of SP600125-induced Dami and CMK cells, and it was not blocked by H-89 despite the increased phosphorylation of S6K1 at Thr389 in both cell lines in response to H-89. Given that the Dami and CMK cell lines were derived from patients with acute megakaryocytic leukemia (AMKL) and expressed high levels of platelet-specific antigens, our data suggested that SP600125-induced polyploidization is cell-type specific, that these cell lines were more differentiated, and that phosphorylation at Thr421/Ser424 and dephosphorylation at Thr389 of S6K1 may play an important role in the SP600125-induced polyploidization of these cell lines synergistically with other signaling pathways.

Inhibition of mTOR pathway sensitizes acute myeloid leukemia cells to aurora inhibitors by suppression of glycolytic metabolism

Aurora kinases are overexpressed in large numbers of tumors and considered as potential therapeutic targets. In this study, we found that the Aurora kinases inhibitors MK-0457 (MK) and ZM447439 (ZM) induced polyploidization in acute myeloid leukemia (AML) cell lines. The level of glycolytic metabolism was significantly increased in the polyploidy cells, which were sensitive to glycolysis inhibitor 2-deoxy-D-glucose (2DG), suggesting that polyploidy cells might be eliminated by metabolism deprivation. Indeed, inhibition of mTOR pathway by mTOR inhibitors (rapamycin and PP242) or 2DG promoted not only apoptosis but also autophagy in the polyploidy cells induced by Aurora inhibitors. Mechanically, PP242 or2DGdecreased the level of glucose uptake and lactate production in polyploidy cells as well as the expression of p62/SQSTM1. Moreover, knockdown of p62/SQSTM1 sensitized cells to the Aurora inhibitor whereas overexpression of p62/SQSTM1 reduced drug efficacy. Thus, our results revealed that inhibition of mTOR pathway decreased the glycolytic metabolism of the polyploidy cells, and increased the efficacy of Aurora kinases inhibitors, providing a novel approach of combination treatment in AML.

Association of maternal mRNA and phosphorylated EIF4EBP1 variants with the spindle in mouse oocytes: localized translational control supporting female meiosis in mammals

In contrast to other species, localized maternal mRNAs are not believed to be prominent features of mammalian oocytes. We find by cDNA microarray analysis enrichment for maternal mRNAs encoding spindle and other proteins on the mouse oocyte metaphase II (MII) spindle. We also find that the key translational regulator, EIF4EBP1, undergoes a dynamic and complex spatially regulated pattern of phosphorylation at sites that regulate its association with EIF4E and its ability to repress translation. These phosphorylation variants appear at different positions along the spindle at different stages of meiosis. These results indicate that dynamic spatially restricted patterns of EIF4EBP1 phosphorylation may promote localized mRNA translation to support spindle formation, maintenance, function, and other nearby processes. Regulated EIF4EBP1 phosphorylation at the spindle may help coordinate spindle formation with progression through the cell cycle. The discovery that EIF4EBP1 may be part of an overall mechanism that integrates and couples cell cycle progression to mRNA translation and subsequent spindle formation and function may be relevant to understanding mechanisms leading to diminished oocyte quality, and potential means of avoiding such defects. The localization of maternal mRNAs at the spindle is evolutionarily conserved between mammals and other vertebrates and is also seen in mitotic cells, indicating that EIF4EBP1 control of localized mRNA translation is likely key to correct segregation of genetic material across cell types.

Arabidopsis S6 kinase mutants display chromosome instability and altered RBR1-E2F pathway activity

The 40S ribosomal protein S6 kinase (S6K) is a conserved component of signalling pathways controlling growth in eukaryotes. To study S6K function in plants, we isolated single- and double-knockout mutations and RNA-interference (RNAi)-silencing lines in the linked Arabidopsis S6K1 and S6K2 genes. Hemizygous s6k1s6k2/++ mutant and S6K1 RNAi lines show high phenotypic instability with variation in size, increased trichome branching, produce non-viable pollen and high levels of aborted seeds. Analysis of their DNA content by flow cytometry, as well as chromosome counting using DAPI staining and fluorescence in situ hybridization, revealed an increase in ploidy and aneuploidy. In agreement with this data, we found that S6K1 associates with the Retinoblastoma-related 1 (RBR1)-E2FB complex and this is partly mediated by its N-terminal LVxCxE motif. Moreover, the S6K1-RBR1 association regulates RBR1 nuclear localization, as well as E2F-dependent expression of cell cycle genes. Arabidopsis cells grown under nutrient-limiting conditions require S6K for repression of cell proliferation. The data suggest a new function for plant S6K as a repressor of cell proliferation and required for maintenance of chromosome stability and ploidy levels.