A regulatory feedback loop between HIF-1α and PIM2 in HepG2 cells

Targeting Echinococcus multilocularis PIM kinase for improving anti-parasitic chemotherapy

BACKGROUND

The potentially lethal zoonosis alveolar echinococcosis (AE) is caused by the metacestode larval stage of the tapeworm Echinococcus multilocularis. Current AE treatment options are limited and rely on surgery as well as on chemotherapy involving benzimidazoles (BZ). BZ treatment, however, is mostly parasitostatic only, must be given for prolonged time periods, and is associated with adverse side effects. Novel treatment options are thus urgently needed.

METHODOLOGY/PRINCIPAL FINDINGS

By applying a broad range of kinase inhibitors to E. multilocularis stem cell cultures we identified the proto-oncogene PIM kinase as a promising target for anti-AE chemotherapy. The gene encoding the respective E. multilocularis ortholog, EmPim, was characterized and in situ hybridization assays indicated its expression in parasite stem cells. By yeast two-hybrid assays we demonstrate interaction of EmPim with E. multilocularis CDC25, indicating an involvement of EmPim in parasite cell cycle regulation. Small molecule compounds SGI-1776 and CX-6258, originally found to effectively inhibit human PIM kinases, exhibited detrimental effects on in vitro cultured parasite metacestode vesicles and prevented the formation of mature vesicles from parasite stem cell cultures. To improve compound specificity for EmPim, we applied a high throughput in silico modelling approach, leading to the identification of compound Z196138710. When applied to in vitro cultured metacestode vesicles and parasite cell cultures, Z196138710 proved equally detrimental as SGI-1776 and CX-6258 but displayed significantly reduced toxicity towards human HEK293T and HepG2 cells.

CONCLUSIONS/SIGNIFICANCE

Repurposing of kinase inhibitors initially designed to affect mammalian kinases for helminth disease treatment is often hampered by adverse side effects of respective compounds on human cells. Here we demonstrate the utility of high throughput in silico approaches to design small molecule compounds of higher specificity for parasite cells. We propose EmPim as a promising target for respective approaches towards AE treatment.

The Role of PIM Kinases in Pediatric Solid Tumors

PIM kinases have been identified as potential therapeutic targets in several malignancies. Here, we provide an in-depth review of PIM kinases, including their structure, expression, activity, regulation, and role in pediatric carcinogenesis. Also included is a brief summary of the currently available pharmaceutical agents targeting PIM kinases and existing clinical trials.

CXCL2 benefits acute myeloid leukemia cells in hypoxia

INTRODUCTION

Drug resistance and relapse of acute myeloid leukemia (AML) is still an important problem in the treatment of leukemia. Leukemia outbreak causes severe hypoxia in bone marrow (BM), remolding BM microenvironment (niche), and transforming hematopoietic stem cell (HSC) niche into leukemia stem cell (LSC) niche. AML cells and the microenvironment usually conduct "cross-talk" through cytokines to anchor resistant AML cells into LSC niche, thus supporting their survival. Therefore, this study was aimed to investigate the role of CXCL2 in the hypoxic AML niche.

METHODS

AML hypoxic niche was simulated by hypoxic culture of THP-1 and HL-60 cells in vitro, thus to study the effects of CXCL2 on the proliferation and migration of AML cells. The expression of hypoxia-inducible factor-1α (HIF-1α) and the activation of survival-related kinases such as PIM2 and mTOR under CoCl₂ -simulated hypoxic conditions were detected. The correlation between CXCL2 and the prognosis of AML with big data was verified.

RESULTS

(a) CXCL2 promoted the proliferation and migration of AML cells. (b) CXCL2 up-regulated the expression of PIM2 by enhancing the transcriptional activity of HIF-1α. (c) CXCL2 activated mTOR in AML cells. (d) CXCL2 was associated with poor prognosis in AML.

CONCLUSION

CXCL2 promotes survival, migration, and drug resistance pathway of AML cells in hypoxia and is associated with poor prognosis in AML. Therefore, CXCL2 can be considered as an important factor in promoting the development of AML cells in hypoxia.

Protein kinase PIM2: A simple PIM family kinase with complex functions in cancer metabolism and therapeutics

PIM2 (proviral integration site for Moloney murine leukemia virus 2) kinase plays an important role as an oncogene in multiple cancers, such as leukemia, liver, lung, myeloma, prostate and breast cancers. PIM2 is largely expressed in both leukemia and solid tumors, and it promotes the transcriptional activation of genes involved in cell survival, cell proliferation, and cell-cycle progression. Many tumorigenic signaling molecules have been identified as substrates for PIM2 kinase, and a variety of inhibitors have been developed for its kinase activity, including SMI-4a, SMI-16a, SGI-1776, JP11646 and DHPCC-9. Here, we summarize the signaling pathways involved in PIM2 kinase regulation and PIM2 mechanisms in various neoplastic diseases. We also discuss the current status and future perspectives for the development of PIM2 kinase inhibitors to combat human cancer, and PIM2 will become a therapeutic target in cancers in the future.

Phosphorylation of HSF1 by PIM2 Induces PD-L1 Expression and Promotes Tumor Growth in Breast Cancer

Heat shock transcription factor 1 (HSF1) is the master regulator of the proteotoxic stress response, which plays a key role in breast cancer tumorigenesis. However, the mechanisms underlying regulation of HSF1 protein stability are still unclear. Here, we show that HSF1 protein stability is regulated by PIM2-mediated phosphorylation of HSF1 at Thr120, which disrupts the binding of HSF1 to the E3 ubiquitin ligase FBXW7. In addition, HSF1 Thr120 phosphorylation promoted proteostasis and carboplatin-induced autophagy. Interestingly, HSF1 Thr120 phosphorylation induced HSF1 binding to the PD-L1 promoter and enhanced PD-L1 expression. Furthermore, HSF1 Thr120 phosphorylation promoted breast cancer tumorigenesis in vitro and in vivo. PIM2, pThr120-HSF1, and PD-L1 expression positively correlated with each other in breast cancer tissues. Collectively, these findings identify PIM2-mediated HSF1 phosphorylation at Thr120 as an essential mechanism that regulates breast tumor growth and potential therapeutic target for breast cancer. SIGNIFICANCE: These findings identify heat shock transcription factor 1 as a new substrate for PIM2 kinase and establish its role in breast tumor progression.

Negative regulation of AMPKα1 by PIM2 promotes aerobic glycolysis and tumorigenesis in endometrial cancer

Endometrial cancer (EC) is one of the most common gynecologic malignancies. However, the molecular mechanisms underlying the development and progression of EC remain unclear. Here, we demonstrated that the protein proviral insertion in murine lymphomas 2 (PIM2) was necessary for maintaining EC tumorigenesis in vivo and in vitro, and could inhibit AMPKα1 kinase activity in EC cells. Specifically, we found that PIM2 bound to AMPKα1, and directly phosphorylated it on Thr467. Phosphorylation of AMPKα1 by PIM2 led to decreasing AMPKα1 kinase activity, which in turn promoted aerobic glycolysis and tumor growth. In addition, PIM2 expression positively correlated with AMPKα1 Thr467 phosphorylation in EC tissues. Further, treatment with a combination of the PIM2 inhibitor SMI-4a and the AMPKα1 activator AICAR could effectively inhibit tumor growth. Thus, our findings provide insight into the role of PIM2 and AMPKα1 in EC and suggest that combination targeting of these proteins may represent a new strategy for EC treatment.

PIM2-mediated phosphorylation of hexokinase 2 is critical for tumor growth and paclitaxel resistance in breast cancer

Hexokinase-II (HK2) is a key enzyme involved in glycolysis, which is required for breast cancer progression. However, the underlying post-translational mechanisms of HK2 activity are poorly understood. Here, we showed that Proviral Insertion in Murine Lymphomas 2 (PIM2) directly bound to HK2 and phosphorylated HK2 on Thr473. Biochemical analyses demonstrated that phosphorylated HK2 Thr473 promoted its protein stability through the chaperone-mediated autophagy (CMA) pathway, and the levels of PIM2 and pThr473-HK2 proteins were positively correlated with each other in human breast cancer. Furthermore, phosphorylation of HK2 on Thr473 increased HK2 enzyme activity and glycolysis, and enhanced glucose starvation-induced autophagy. As a result, phosphorylated HK2 Thr473 promoted breast cancer cell growth in vitro and in vivo. Interestingly, PIM2 kinase inhibitor SMI-4a could abrogate the effects of phosphorylated HK2 Thr473 on paclitaxel resistance in vitro and in vivo. Taken together, our findings indicated that PIM2 was a novel regulator of HK2, and suggested a new strategy to treat breast cancer.

PIM-2 protein kinase negatively regulates T cell responses in transplantation and tumor immunity

PIM kinase family members play a crucial role in promoting cell survival and proliferation via phosphorylation of their target substrates. In this study, we investigated the role of the PIM kinases with respect to T cell responses in transplantation and tumor immunity. We found that the PIM-2 isoform negatively regulated T cell responses to alloantigen, in contrast to the PIM-1 and PIM-3 isoforms, which acted as positive regulators. T cells deficient in PIM-2 demonstrated increased T cell differentiation toward Th1 subset, proliferation, and migration to target organs after allogeneic bone marrow transplantation, resulting in dramatically accelerated graft-versus-host disease (GVHD) severity. Restoration of PIM-2 expression markedly attenuated the pathogenicity of PIM-2-deficient T cells to induce GVHD. On the other hand, mice deficient in PIM-2 readily rejected syngeneic tumor, which was primarily dependent on CD8+ T cells. Furthermore, silencing PIM-2 in polyclonal or antigen-specific CD8+ T cells substantially enhanced their antitumor response in adoptive T cell immunotherapy. We conclude that PIM-2 kinase plays a prominent role in suppressing T cell responses, and provide a strong rationale to target PIM-2 for cancer immunotherapy.

PIM2 interacts with tristetraprolin and promotes breast cancer tumorigenesis

Tristetraprolin (TTP) is an AU‐rich element‐binding protein that regulates mRNA stability and plays important roles in cancer. The mechanisms by which TTP is regulated in breast cancer are poorly understood. Using multiple biochemical approaches, we found that proviral insertion in murine lymphomas 2 (PIM2) is a novel binding partner of TTP. Interestingly, PIM2 decreased TTP protein levels independent of its kinase activity. PIM2 instead targeted TTP protein for degradation via the ubiquitin‐proteasome pathway. Furthermore, immunohistochemical staining showed that PIM2 and TTP protein levels were negatively correlated in human breast cancer samples. Indeed, PIM2 overexpression de‐repressed TTP‐mediated inhibition of breast cancer cell proliferation and migration in vitro and promoted breast tumor xenograft growth in vivo. These findings demonstrate an important role for the PIM2‐TTP complex in breast cancer tumorigenesis, suggesting that PIM2 may represent a potential therapeutic target for breast cancer treatment.

mTORC1 suppresses PIM3 expression via miR-33 encoded by the SREBP loci

The mechanistic target of rapamycin complex 1 (mTORC1) is a central regulator of cell growth that is often aberrantly activated in cancer. However, mTORC1 inhibitors, such as rapamycin, have limited effectiveness as single agent cancer therapies, with feedback mechanisms inherent to the signaling network thought to diminish the anti-tumor effects of mTORC1 inhibition. Here, we identify the protein kinase and proto-oncogene PIM3 as being repressed downstream of mTORC1 signaling. PIM3 expression is suppressed in cells with loss of the tuberous sclerosis complex (TSC) tumor suppressors, which exhibit growth factor-independent activation of mTORC1, and in the mouse liver upon feeding-induced activation of mTORC1. Inhibition of mTORC1 with rapamycin induces PIM3 transcript and protein levels in a variety of settings. Suppression of PIM3 involves the sterol regulatory element-binding (SREBP) transcription factors SREBP1 and 2, whose activation and mRNA expression are stimulated by mTORC1 signaling. We find that PIM3 repression is mediated by miR-33, an intronic microRNA encoded within the SREBP loci, the expression of which is decreased with rapamycin. These results demonstrate that PIM3 is induced upon mTORC1 inhibition, with potential implications for the effects of mTORC1 inhibitors in TSC, cancers, and the many other disease settings influenced by aberrant mTORC1 signaling.

Novel inhibition of PIM2 kinase has significant anti-tumor efficacy in multiple myeloma

The PIM kinase family (PIM1, 2 and 3) have a central role in integrating growth and survival signals, and are expressed in a wide range of solid and hematological malignancies. We now confirm that PIM2 is overexpressed in multiple myeloma (MM) patients, and within MM group it is overexpressed in the high-risk MF subset (activation of proto-oncogenes MAF/MAFB). This is consistent with our finding of PIM2's role in key signaling pathways (IL-6, CD28 activation) that confer chemotherapy resistance in MM cells. These studies have identified a novel PIM2-selective non-ATP competitive inhibitor (JP11646) that has a 4 to 760-fold greater suppression of MM proliferation and viability than ATP-competitive PIM inhibitors. This increased efficacy is due not only to the inhibition of PIM2 kinase activity, but also to a novel mechanism involving specific downregulation of PIM2 mRNA and protein expression not seen with the ATP competitive inhibitors. Treatment with JP11646 in xenogeneic myeloma murine models demonstrated significant reduction in tumor burden and increased median survival. Altogether our findings suggest the existence of previously unrecognized feedback loop(s) where PIM2 kinase activity regulates PIM2 gene expression in malignant cells, and that JP11646 represents a novel class of PIM2 inhibitors that interdicts this feedback.

PKM2 Thr454 phosphorylation increases its nuclear translocation and promotes xenograft tumor growth in A549 human lung cancer cells

Pyruvate kinase M2 (PKM2) is a key enzyme of glycolysis which is highly expressed in many tumor cells, and plays an important role in the Warburg effect. In previous study, we found PIM2 phosphorylates PKM2 at Thr454 residue (Yu, etl 2013). However, the functions of PKM2 Thr454 modification in cancer cells still remain unclear. Here we find PKM2 translocates into the nucleus after Thr454 phosphorylation. Replacement of wild type PKM2 with a mutant (T454A) enhances mitochondrial respiration, decreases pentose phosphate pathway, and enhances chemosensitivity in A549 cells. In addition, the mutant (T454A) PKM2 reduces xenograft tumor growth in nude mice. These findings demonstrate that PKM2 T454 phosphorylation is a potential therapeutic target in lung cancer.

Chinese Herbs Interfering with Cancer Reprogramming Metabolism

Emerging evidence promotes a reassessment of metabolic reprogramming regulation in cancer research. Although there exists a long history of Chinese herbs applied in cancer treatment, few reports have addressed the effects of Chinese herbal components on metabolic reprogramming, which is a central cancer hallmark involved in the slowing or prevention of chemoresistance in cancer cells. In this review, we have focused on four core elements altered by metabolic reprogramming in cancer cells. These include glucose transport, glycolysis, mitochondrial oxidative phosphorylation, and fatty acid synthesis. With this focus, we have summarized recent advances in metabolic reprogramming of cancer cells in response to specific Chinese herbal components. We propose that exploring Chinese herbal interference in cancer metabolic reprogramming might identify new therapeutic targets for cancer and more ways in which to approach metabolism-related diseases.

Interaction with Pyruvate Kinase M2 Destabilizes Tristetraprolin by Proteasome Degradation and Regulates Cell Proliferation in Breast Cancer

Pyruvate kinase M2 (PKM2), which is predominantly expressed in most cancers, plays a key role in the Warburg effect. However, how PKM2 functions as a tumor supportive protein has not been fully elucidated. Here, we identified tristetraprolin (TTP), an AU-rich, element-binding protein that regulates mRNA stability, as a new binding partner of PKM2. Our data reveal that PKM2 suppresses TTP protein levels by promoting its phosphorylation, ubiquitination, and proteasome degradation, reducing its mRNA turnover ability and ultimately impairing cell viability in breast cancer cells. The p38/mitogen-activated protein kinase (MAPK) pathway might be involved in PKM2-mediated TTP degradation, while treatment with the p38 inhibitor or siRNA abolished PKM2-induced TTP protein degradation. These findings demonstrate that PKM2-TTP association is crucial for regulating breast cancer cell proliferation and is therefore a potential therapeutic target in cancer.

Elevated PIM2 gene expression is associated with poor survival of patients with acute myeloid leukemia

The PIM2 gene encodes the serine/threonine kinase involved in cell survival and apoptosis. The aim of the study was to evaluate the expression of the PIM2 gene in acute myeloid leukemia (AML) and to examine its role in apoptosis of the blastic cells. We analyzed the PIM2 expression in 148 patients: 91 with AML, 57 with acute lymphoblastic leukemia and 24 healthy controls by Real-Time PCR and Western blot. Inhibition of the PIM2 gene in human leukemic HL60 cell line was performed with RNAi and apoptosis rate was analyzed. Our results indicate that overexpression of PIM2 in AML is associated with low complete remission rate, high-risk cytogenetics, shorter leukemia-free survival, and event-free survival. Cytometric analysis of HL60/PAC-GFP and HL60/PAC-GFP-shPIM2 cells revealed an increase in the number of apoptotic cells after inhibition of PIM2 gene. In summary, the elevated expression of PIM2 in blastic cells is associated with poor prognosis of AML patients and their resistance to induction therapy.

PIM kinase (and Akt) biology and signaling in tumors

The initiation and progression of human cancer is frequently linked to the uncontrolled activation of survival kinases. Two such pro-survival kinases that are commonly amplified in cancer are PIM and Akt. These oncogenic proteins are serine/threonine kinases that regulate tumorigenesis by phosphorylating substrates that control the cell cycle, cellular metabolism, proliferation, and survival. Growing evidence suggests that cross-talk exists between the PIM and Akt kinases, indicating that they control partially overlapping survival signaling pathways that are critical to the initiation, progression, and metastatic spread of many types of cancer. The PI3K/Akt signaling pathway is activated in many human tumors, and it is well established as a promising anticancer target. Likewise, based on the role of PIM kinases in normal and tumor tissues, it is clear that this family of kinases represents an interesting target for anticancer therapy. Pharmacological inhibition of PIM has the potential to significantly influence the efficacy of standard and targeted therapies. This review focuses on the regulation of PIM kinases, their role in tumorigenesis, and the biological impact of their interaction with the Akt signaling pathway on the efficacy of cancer therapy.

Pim-2 Modulates Aerobic Glycolysis and Energy Production during the Development of Colorectal Tumors

Tumor cells have higher rates of glucose uptake and aerobic glycolysis to meet energy demands for proliferation and metastasis. The characteristics of increased glucose uptake, accompanied with aerobic glycolysis, has been exploited for the diagnosis of cancers. Although much progress has been made, the mechanisms regulating tumor aerobic glycolysis and energy production are still not fully understood. Here, we demonstrate that Pim-2 is required for glycolysis and energy production in colorectal tumor cells. Our results show that Pim-2 is highly expressed in colorectal tumor cells, and may be induced by nutrient stimulation. Activation of Pim-2 in colorectal cells led to increase glucose utilization and aerobic glycolysis, as well as energy production. While knockdown of Pim-2 decreased energy production in colorectal tumor cells and increased their susceptibility to apoptosis. Moreover, the effects of Pim-2 kinase on aerobic glycolysis seem to be partly dependent on mTORC1 signaling, because inhibition of mTORC1 activity reversed the aerobic glycolysis mediated by Pim-2. Our findings suggest that Pim-2-mediated aerobic glycolysis is critical for monitoring Warburg effect in colorectal tumor cells, highlighting Pim-2 as a potential metabolic target for colorectal tumor therapy.

Neuroprotection by Orexin-A via HIF-1α induction in a cellular model of Parkinson's disease

Orexin-A, a neuropeptide secreted by hypothalamic neurons, may be neuroprotective in many neurological conditions such as cerebral ischaemia. One mechanism postulated to be involved in the neuroprotection by Orexin-A is the induction of hypoxia inducible factor 1 alpha (HIF-1α). Parkinson's disease (PD) is a progressive neurodegenerative disorder and mitochondrial dysfunction has been demonstrated to play a role in its pathogenesis. Mitochondrial dysfunction may cause reduction of O2 consumption and subsequently activate prolyl hydroxylase, which leads to decreased level of HIF-1α. In this study, we used MPP(+)-treated SH-SY5Y cells as an in vitro cellular model of PD to test the role of Orexin-A as an inducer of HIF-1α. Our results showed that Orexin-A not only induced HIF-1α but also activated downstream targets of HIF-1α, such as vascular endothelial growth factor and erythropoietin. Thus, Orexin-A treatment attenuated MPP(+)-induced cell injury and this effect was blocked when HIF-1α was suppressed. Hence, we conclude that induction of HIF-1α is one of the mechanisms involved in the neuroprotection by Orexin-A.