Mcl-1 Stability Research Articles

The CDK inhibitor purvalanol A induces neutrophil apoptosis and increases the turnover rate of Mcl-1: potential role of p38-MAPK in regulation of Mcl-1 turnover.

Human neutrophils are terminally differentiated cells that do not replicate and yet express a number of enzymes, notably cell cycle-dependent kinases (CDKs), that are associated normally with control of DNA synthesis and cell cycle progression. In neutrophils, CDKs appear to function mainly to regulate apoptosis, although the mechanisms by which they regulate this process are largely unknown. Here we show that the CDK2 inhibitor, purvalanol A, induces a rapid decrease in myeloid cell leukaemia factor-1 (Mcl-1) levels in human neutrophils and peripheral blood mononuclear cells (PBMCs), but only induces apoptosis in neutrophils which are dependent upon expression on this protein for survival. This rapid decrease in cellular Mcl-1 protein levels was due to a purvalanol A-induced decrease in stability, with the half-life of the protein decreasing from approximately 2h in control cells to just over 1h after addition of the CDK2 inhibitor: it also blocked the granulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent stabilization of Mcl-1. Purvanalol A blocked GM-CSF-stimulated activation of extracellular-regulated kinase (Erk) and signal transducer and activator of transcription (STAT)-3, and stimulated an additive activation of protein kinase B (Akt) with GM-CSF. Purvalanol A alone stimulated a rapid and sustained activation of p38-mitogen-activated protein kinase (MAPK) and the pan p38-MAPK inhibitor, BIRB796, partly blocked the purvalanol A-induced apoptosis and Mcl-1 loss. These novel effects of purvalanol A may result, at least in part, from blocking GM-CSF-mediated Erk activation. In addition, we propose that purvalanol A-induced activation of p38-MAPK is, at least in part, responsible for its rapid effects on Mcl-1 turnover and acceleration of neutrophil apoptosis.

Deubiquitinase USP13 dictates MCL1 stability and sensitivity to BH3 mimetic inhibitors

MCL1 is a pivot member of the anti-apoptotic BCL-2 family proteins. While a distinctive feature of MCL1 resides in its efficient ubiquitination and destruction, the deubiquitinase USP9X has been implicated in the preservation of MCL1 expression by removing the polyubiquitin chains. Here we perform an unbiased siRNA screen and identify that the second deubiquitinase, USP13, regulates MCL1 stability in lung and ovarian cancer cells. Mechanistically, USP13 interacts with and stabilizes MCL1 via deubiquitination. As a result, USP13 depletion using CRISPR/Cas9 nuclease system inhibits tumor growth in xenografted nude mice. We further report that genetic or pharmacological inhibition of USP13 considerably reduces MCL1 protein abundance and significantly increases tumor cell sensitivity to BH3 mimetic inhibitors targeting BCL-2 and BCL-XL. Collectively, we nominate USP13 as a novel deubiquitinase which regulates MCL1 turnover in diverse solid tumors and propose that USP13 may be a potential therapeutic target for the treatment of various malignancies.

Mcl-1 stabilization confers resistance to taxol in human gastric cancer.

Taxol has been extensively used as an antineoplastic drug to treat human gastric cancer. However, the acquired drug resistance invariably develops and greatly limits the therapeutic efficacy of Taxol. Identification of the underlying resistance mechanisms may inform the development of new therapies of gastric cancers to Taxol treatment. Here we report that upregulation of Mcl-1 (Myeloid cell leukemia-1) confers acquired resistance to Taxol in human gastric cancer. Mcl-1 is shown to be stabilized in Taxol -resistant gastric cancer cells because of the hyper-activation of the PI3K/Akt signaling pathway. The increased Mcl-1 prevents of the permeabilization of the outer mitochondrial membrane, thereby blocking the Taxol-induced apoptosis. Furthermore, inhibition of Mcl-1 or PI3K/Akt pathway significantly reversed the resistant phenotype of Taxol-resistant human gastric cancer cells. Taken together, our findings broaden the view of PI3K/Akt pathway as an important regulator in Taxol acquired resistance, and implicate Mcl-1 as a specific therapeutic target for the treatment of Taxol-resistant human gastric cancer.

FBXO4 inhibits lung cancer cell survival by targeting Mcl-1 for degradation

Mcl-1 (myeloid cell leukemia 1) is a prosurvival member of the Bcl-2 family and plays a critical role in cell survival by suppressing apoptosis through inhibiting the activity of proapoptotic proteins. It has been reported that Mcl-1 is frequently overexpressed in lung cancer. However, the exact molecular mechanism underlying Mcl-1 elevation in lung cancer is largely unknown. Here, we reported that Mcl-1 protein levels inversely correlate with FBXO4 expression, but not other F-box proteins examined, in lung cancer cell lines and lung cancer patient samples. Mechanically, FBXO4 is the E3 ubiquitin ligase to interact with and promote Mcl-1 ubiquitination and degradation. As a result, knockdown of Fbxo4 dramatically elevates Mcl-1 protein levels and increases cell survival and resistance to chemotherapeutic drugs, whereas ectopic expression of FBXO4 displays opposite phenotypes. Therefore, our study suggests that the protein stability of Mcl-1 is governed by FBXO4, which plays an important role in cell survival and chemotherapy for lung cancer.

Targeting FBW7 as a Strategy to Overcome Resistance to Targeted Therapy in Non-Small Cell Lung Cancer.

Inhibition of EGFR and anaplastic lymphoma kinase (ALK) signaling is highly effective in a subgroup of non-small cell lung cancer (NSCLC) patients with distinct clinicopathologic features. However, resistance to EGFR and ALK inhibitors inevitably occurs, and the molecular mechanism underlying resistance is not fully understood. In this study, we report a PI3K/Akt- and MEK/ERK-independent resistance mechanism by which loss of the E3 ubiquitin ligase F-box and WD repeat domain containing 7 (FBW7α) leads to targeted therapy resistance via stabilization of antiapoptotic protein MCL-1. Using a panel of in vitro and in vivo studies, we showed that the regulatory machinery responsible for MCL-1 protein degradation was a step-wise event involving phosphorylation and nucleus translocation. ERK cooperated with GSKβ to phosphorylate MCL-1 Ser159 residue, which enabled MCL-1 to translocate into the nucleus and bind FBW7. Defects in this sequence impaired MCL-1 degradation and cell apoptosis, recapitulating phenotypes observed in FBW7 deficiency. Downregulation of FBW7 was found in EGFR inhibitor-resistant human NSCLC specimens and correlated with increased MCL-1 protein expression. Reactivation of FBW7 sensitized resistant cells to targeted therapy and facilitated MCL-1 degradation. Overall, our study provides proof-of-principle insight into a PI3K/Akt- and MEK/ERK-independent resistant model and suggests that targeting FBW7 can overcome resistance to targeted therapy. Cancer Res; 77(13); 3527-39. ©2017 AACR.

STK11 Loss Stabilizes MCL1 and Confers Targetable Drug Resistance in KRAS Mutant NSCLC

The combined KRAS/STK11 (serine‐threonine kinase 11, LKB1) mutated genotype is prevalent and predictive of poor clinical outcome in NSCLC as tumors are drug resistant. Here, we demonstrate that the bromodomain and extraterminal inhibitor (BETi) JQ1 can induce apoptosis in KRASm NSCLC by targeting the pro‐apoptotic BIM anti‐apoptotic BCL2/BCL‐XL axis, but not in KRASm/STK11m due to additional elevated MCL1. Specifically, loss of STK11 stabilizes anti‐apoptotic MCL1 protein via activation of the PI3K‐mTOR signaling axis. In NSCLC cell line models, we have demonstrated that overexpressing myristoylated‐PI3K increased MCL1 expression whereas the PI3K/mTOR inhibitor BEZ235 reduced MCL1 in a dose, time, and proteasome‐dependent, yet relatively GSK3β‐independent, manner. Furthermore, MCL1 stability also attenuates the antitumor efficacy of the direct BCL2/BCL‐XL inhibitor, ABT‐263 (Navitoclax) in KRASm/STK11m cells. However, combination of BETi or ABT‐263 with MCL1 protein reduction by siRNA or BEZ235, or direct MCL1 inhibition by the BH3 mimetic, A1210477, could sensitize resistant cells to apoptosis while no monotherapy was effective. Therefore, STK11 mutation or aberrant PI3K/mTOR pathway activations emerge as biomarkers of BET‐ or BCL2/BCL‐XL inhibitor resistance, suggesting patient selection for combined MCL1 inhibition.Support or Funding InformationThis work is supported by research Scholar grant RSG‐14‐229‐01 from the American Cancer Society and United Against Lung Cancer Legacy Program (Lung Cancer Research Foundation). This work is also supported by research fellowship from Sumitomo life social welfare services foundation (E.K), MINECO (SAF2010‐21769), ISCIII (RD12/0036/0045) and Generalitat Valenciana (ACOMP/2013/156 and ACIF/2013/239) (J.C.), and National Institutes of Health grants CA140594, CA122794, CA163896, CA166480 (K.K.W)

Chlamydia trachomatis-containing vacuole serves as deubiquitination platform to stabilize Mcl-1 and to interfere with host defense.

Obligate intracellular Chlamydia trachomatis replicate in a membrane-bound vacuole called inclusion, which serves as a signaling interface with the host cell. Here, we show that the chlamydial deubiquitinating enzyme (Cdu) 1 localizes in the inclusion membrane and faces the cytosol with the active deubiquitinating enzyme domain. The structure of this domain revealed high similarity to mammalian deubiquitinases with a unique α-helix close to the substrate-binding pocket. We identified the apoptosis regulator Mcl-1 as a target that interacts with Cdu1 and is stabilized by deubiquitination at the chlamydial inclusion. A chlamydial transposon insertion mutant in the Cdu1-encoding gene exhibited increased Mcl-1 and inclusion ubiquitination and reduced Mcl-1 stabilization. Additionally, inactivation of Cdu1 led to increased sensitivity of C. trachomatis for IFNγ and impaired infection in mice. Thus, the chlamydial inclusion serves as an enriched site for a deubiquitinating activity exerting a function in selective stabilization of host proteins and protection from host defense.

Macrophages confer survival signals via CCR1-dependent translational MCL-1 induction in chronic lymphocytic leukemia

Protective interactions with bystander cells in micro-environmental niches, such as lymph nodes (LNs), contribute to survival and therapy resistance of chronic lymphocytic leukemia (CLL) cells. This is caused by a shift in expression of B-cell lymphoma 2 (BCL-2) family members. Pro-survival proteins B-cell lymphoma-extra large (BCL-XL), BCL-2-related protein A1 (BFL-1) and myeloid leukemia cell differentiation protein 1 (MCL-1) are upregulated by LN-residing T cells through CD40L interaction, presumably via nuclear factor (NF)-κB signaling. Macrophages (Mφs) also reside in the LN, and are assumed to provide important supportive functions for CLL cells. However, if and how Mφs are able to induce survival is incompletely known. We first established that Mφs induced survival because of an exclusive upregulation of MCL-1. Next, we investigated the mechanism underlying MCL-1 induction by Mφs in comparison with CD40L. Genome-wide expression profiling of in vitro Mφ- and CD40L-stimulated CLL cells indicated activation of the phosphoinositide 3-kinase (PI3K)-V-Akt murine thymoma viral oncogene homolog (AKT)-mammalian target of rapamycin (mTOR) pathway, which was confirmed in ex vivo CLL LN material. Inhibition of PI3K-AKT-mTOR signaling abrogated MCL-1 upregulation and survival by Mφs, as well as CD40 stimulation. MCL-1 can be regulated at multiple levels, and we established that AKT leads to increased MCL-1 translation, but does not affect MCL-1 transcription or protein stabilization. Furthermore, among Mφ-secreted factors that could activate AKT, we found that induction of MCL-1 and survival critically depended on C-C motif chemokine receptor-1 (CCR1). In conclusion, this study indicates that two distinct micro-environmental factors, CD40L and Mφs, signal via CCR1 to induce AKT activation resulting in translational stabilization of MCL-1, and hence can contribute to CLL cell survival.

Mutant BRAF upregulates MCL-1 to confer apoptosis resistance that is reversed by MCL-1 antagonism and cobimetinib in colorectal cancer.

603 Background: Oncogenic BRAFV600E mutations activate MAP kinase signaling and are associated with treatment resistance and poor prognosis in patients with colorectal cancer (CRC). In BRAFV600E mutant CRCs, treatment failure may be related to BRAFV600E-mediated apoptosis resistance that occurs by an as yet undefined mechanism. Methods: BRAF isogenic RKO CRC cells and RKO, HT29, WiDr cell lines were treated with cobimetinib ± the small molecule MCL-1 inhibitor, A-1210477. Apoptosis was measured by Annexin V staining and caspase cleavage. Gene knockdown or overexpression was achieved by lentivirus; ERK siRNA was utilized. Competitive RT-PCR was performed for MCL-1 mRNA expression. HT-29 cells with control or MCL-1 shRNA were xenografted into SCID mice, treated with cobimetinib or vehicle, and tumor volume was measured. Results: We found that BRAFV600E can upregulate anti-apoptotic MCL-1 in a gene dose-dependent manner using CRC cell lines isogenic for BRAF. BRAFV600E-induced MCL-1 upregulation was confirmed by ectopic BRAFV600E expression that activated MEK/ERK signaling to phosphorylate (MCL-1Thr163) and stabilize MCL-1. Upregulation of MCL-1 was mediated by MEK/ERK shown by ERK siRNA that suppressed MCL-1. Stabilization of MCL-1 by phosphorylation was shown by a phosphorylation-mimicking mutant and an unphosphorylated MCL-1 mutant that decreased or increased MCL-1 protein turnover, respectively.MEK /ERK inhibition by cobimetinib suppressed MCL-1 expression/phosphorylation and induced pro-apoptotic BIM to a greater extent than did vemurafenib in BRAFV600E cell lines. MCL-1 knockdown vs control shRNA significantly enhanced cobimetinib-induced apoptosis in vitro and in HT29 colon cancer xenografts. A-1210477 also enhanced cobimetinib-induced apoptosis in vitrothat was due to disruption of the interaction of MCL-1 with pro-apoptotic BAK and BIM. Knockdown of BIM attenuated BAX, but not BAK, activation by cobimetinib plus A-1210477. Conclusions: BRAFV600E-mediated MEK/ERK activation can upregulate MCL-1 by phosphorylation/stabilization to confer apoptosis resistance that can be reversed by MCL-1 antagonism.

Co-targeting translation and proteasome rapidly kills colon cancer cells with mutant RAS/RAF via ER stress.

Colorectal cancers with mutant RAS/RAF are therapy refractory. Deregulated mRNA translation has become an emerging target in cancer treatment. We recently reported that mTOR inhibitors induce apoptosis via ER stress and the extrinsic pathway upon acute inhibition of the eIF4F complex in colon cancer cells and xenografts, while mutant BRAF600E leads to therapeutic resistance via ERK-mediated Mcl-1 stabilization. In this study, we demonstrated that several other translation inhibitors also activate ER stress and the extrinsic apoptotic pathway. Co-targeting translation and proteasome using the combination of Episilvestrol and Bortezomib promoted strong ER stress and rapid killing of colon cancer cells with mutant RAS/RAF in culture and mice. This combination led to marked induction of ER stress and ATF4/CHOP, followed by DR5- and BAX-dependent apoptosis, but unexpectedly with maintained or even increased levels of prosurvival factors such as p-AKT, p-4E-BP1, Mcl-1, and eiF4E targets c-Myc and Bcl-xL. Our study supports that targeting deregulated proteostasis is a promising approach for treating advanced colon cancer via induction of destructive ER stress that overcomes multiple resistance mechanisms associated with translation inhibition.

Chaperone-mediated autophagy promotes lung cancer cell survival through selective stabilization of the pro-survival protein, MCL1

Autophagy is a dynamic recycling system using lysosomal proteolysis that produces new proteins and energy for cellular renovation and homeostasis. Although macroautophagy is known to serve as a survival pathway in many cancer cells, the role of chaperone-mediated autophagy (CMA), a selective protein degradation system, in cancer is not fully understood. Here, we demonstrated that lysosomal proteolysis, but not macroautophagy, attenuated apoptosis induced by the tyrosine kinase inhibitor, crizotinib, in the non-small-cell lung cancer (NSCLC) cell line, EBC1. In EBC1 cells, crizotinib induced BIM-dependent apoptosis, which was enhanced by inhibition of lysosomal proteolysis. Moreover, degradation of the pro-survival protein, MCL1, by the ubiquitin-proteasome system was induced by inhibition of lysosomal proteolysis, and by inhibition of the expression of the CMA mediators, HSC70 (heat shock cognate protein 70 kDa) and LAMP2A (lysosome membrane protein type 2A), suggesting the existence of a CMA-mediated MCL1 stabilization system in cancer cells. Indeed, the same MCL1 stabilization system was also observed in several NSCLC cell lines; in these cells, their specific molecular-targeted drug or ABT-263 (Navitoclax), the specific inhibitor of BCL-2 and BCL-XL, but not of MCL1, effectively induced apoptosis in combination with CMA inhibition. Therefore, our results indicate a novel mechanism of MCL1 stabilization in lung cancers by CMA, and a candidate efficient combination chemotherapy method against lung cancers.

Transformation of Chronic Lymphocytic Leukemia Towards Richter´s Syndrome Is Induced By AKT Activation

Richter's syndrome (RS) is an aggressive transformation of Chronic Lymphocytic Leukemia (CLL) to Diffuse Large B Cell Lymphoma (DLBCL) refractory to current therapies with dismal prognosis. Richter Syndrome arises from CLL cells independent of common DLBCL mutations. Frequently, mutations in p53, CDKN2 or cMyc genes are involved, but a significant proportion displays no specifically acquired driver mutation.We could observe activation of AKT in 6 out 48 Richter syndrome biopsies by positive staining for active phosphorylated AKT while in CLL lymph nodes, DLBCL and Burkitt´s Lymphoma no phospho-AKT by IHC could be observed.However in primary patient CLL cases we could detect varying levels of pAKT by Western blot, elevated levels were identified predominantly in patients harboring high-risk mutations such p53, ATM, NOTCH1 and XPO1. Furthermore, B-cell receptor mediated stimulation of the PI3K/AKT axis provided protection towards genotoxic stress induced apoptosis via post-translation stabilization of MCL1. This provides subsequently a synergistic induction of apoptosis by combining idelalisib and bendamustin.Thus we analyzed the functional impact of AKT signaling using a conditional constitutive allele for AKT (AKT-C) specifically activated using CD19-Cre and Cγ1-Cre fro post-GC-activation. AKT activation alone could not induce a malignant phenotype, however we could demonstrate that Eµ-Tcl-1 mice with AKT-C develop Richter Syndrome. Both in EµTCL1:CD19-CreAKT-C (TCA) and EµTCL1:Cγ1- CreAKT-C (TCγ1A) mice developed a high-grade lymphoma phenotype leading to decreased survival. Transformed cells displayed blastoid characteristics with significantly increased cellular size and the histomorphological features of DLBCL. Large transformed cells show high percentage of KI67-positive staining (>90%) and frequent mitotic figures.Here, AKT-mediated GSK-3b inhibition and subsequent cMyc and Mcl-1 stabilization might transform CLL to RS cells and combinatory treatments with DNA-damaging and PI3K-inhibiting compounds revealed promising therapeutic results. Collectively, we have identified AKT signaling as an oncogenic signaling pathway in progression of CLL towards Richter´s syndrome and generated the first murine Richter Syndrome model (TCA and TCγ1A) providing novel mechanistic insights into the molecular understanding of Richter’s transformation that is amenable to model therapeutic strategies and to address the efficacy of synergistic treatment combinations. DisclosuresKlapper:Roche, Novartis, Amgen, Takeda: Research Funding. Hallek:Amgen: Consultancy, Honoraria, Other: travel support, Research Funding, Speakers Bureau; Mundipharma: Consultancy, Honoraria, Other: travel support, Research Funding, Speakers Bureau; AbbVie: Consultancy, Honoraria, Other: travel support, Research Funding, Speakers Bureau; F. Hoffmann-LaRoche: Consultancy, Honoraria, Other: travel support, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Other: travel support, Research Funding, Speakers Bureau; Janssen-Cilag: Consultancy, Honoraria, Other: travel support, Research Funding, Speakers Bureau; Gilead: Consultancy, Honoraria, Other: travel support, Research Funding, Speakers Bureau.

Mutant BRAF Upregulates MCL-1 to Confer Apoptosis Resistance that Is Reversed by MCL-1 Antagonism and Cobimetinib in Colorectal Cancer.

Oncogenic BRAFV600E mutations activate MAPK signaling and are associated with treatment resistance and poor prognosis in patients with colorectal cancer. In BRAFV600E-mutant colorectal cancers, treatment failure may be related to BRAFV600E-mediated apoptosis resistance that occurs by an as yet undefined mechanism. We found that BRAFV600E can upregulate anti-apoptotic MCL-1 in a gene dose-dependent manner using colorectal cancer cell lines isogenic for BRAF BRAFV600E-induced MCL-1 upregulation was confirmed by ectopic BRAFV600E expression that activated MEK/ERK signaling to phosphorylate (MCL-1Thr163) and stabilize MCL-1. Upregulation of MCL-1 was mediated by MEK/ERK shown by the ability of ERK siRNA to suppress MCL-1. Stabilization of MCL-1 by phosphorylation was shown by a phosphorylation-mimicking mutant and an unphosphorylated MCL-1 mutant that decreased or increased MCL-1 protein turnover, respectively. MEK/ERK inhibition by cobimetinib suppressed MCL-1 expression/phosphorylation and induced proapoptotic BIM to a greater extent than did vemurafenib in BRAFV600E cell lines. MCL-1 knockdown versus control shRNA significantly enhanced cobimetinib-induced apoptosis in vitro and in HT29 colon cancer xenografts. The small-molecule MCL-1 inhibitor, A-1210477, also enhanced cobimetinib-induced apoptosis in vitro that was due to disruption of the interaction of MCL-1 with proapoptotic BAK and BIM. Knockdown of BIM attenuated BAX, but not BAK, activation by cobimetinib plus A-1210477. In summary, BRAFV600E-mediated MEK/ERK activation can upregulate MCL-1 by phosphorylation/stabilization to confer apoptosis resistance that can be reversed by MCL-1 antagonism combined with cobimetinib, suggesting a novel therapeutic strategy against BRAFV600E-mutant CRCs. Mol Cancer Ther; 15(12); 3015-27. ©2016 AACR.

Dual modulation of MCL-1 and mTOR determines the response to sunitinib.

Most patients who initially respond to treatment with the multi-tyrosine kinase inhibitor sunitinib eventually relapse. Therefore, developing a deeper understanding of the contribution of sunitinib's numerous targets to the clinical response or to resistance is crucial. Here, we have shown that cancer cells respond to clinically relevant doses of sunitinib by enhancing the stability of the antiapoptotic protein MCL-1 and inducing mTORC1 signaling, thus evoking little cytotoxicity. Inhibition of MCL-1 or mTORC1 signaling sensitized cells to clinically relevant doses of sunitinib in vitro and was synergistic with sunitinib in impairing tumor growth in vivo, indicating that these responses are triggered as prosurvival mechanisms that enable cells to tolerate the cytotoxic effects of sunitinib. Furthermore, higher doses of sunitinib were cytotoxic, triggered a decline in MCL-1 levels, and inhibited mTORC1 signaling. Mechanistically, we determined that sunitinib modulates MCL-1 stability by affecting its proteasomal degradation. Dual modulation of MCL-1 stability at different dose ranges of sunitinib was due to differential effects on ERK and GSK3β activity, and the latter also accounted for dual modulation of mTORC1 activity. Finally, comparison of patient samples prior to and following sunitinib treatment suggested that increases in MCL-1 levels and mTORC1 activity correlate with resistance to sunitinib in patients.

Amsacrine-induced apoptosis of human leukemia U937 cells is mediated by the inhibition of AKT- and ERK-induced stabilization of MCL1.

Previous studies have attributed the anticancer activity of amsacrine to its inhibitory effect on topoisomerase II. However, 9-aminoacridine derivatives, which have the same structural scaffold as amsacrine, induce cancer cell apoptosis by altering the expression of BCL2 family proteins. Therefore, in the present study, we assessed whether BCL2 family proteins mediated the cytotoxic effects of amsacrine on human leukemia U937 cells. Amsacrine-induced apoptosis of U937 cells was characterized by caspase-9 and caspase-3 activation, increased intracellular Ca2+ concentration, mitochondrial depolarization, and MCL1 down-regulation. Amsacrine induced MCL1 down-regulation by decreasing its stability. Further, amsacrine-treated U937 cells showed AKT degradation and Ca2+-mediated ERK inactivation. Blockade of ERK-mediated phosphorylation of MCL1 inhibited the effect of Pin1 on the stabilization of MCL1, and AKT degradation promoted GSK3β-mediated degradation of MCL1. Restoration of ERK phosphorylation and AKT expression abrogated amsacrine-induced MCL1 down-regulation. Moreover, MCL1 over-expression inhibited amsacrine-induced depolarization of mitochondria membrane and increased the viability of amsacrine-treated cells. Taken together, our data indicate that amsacrine abolishes ERK- and Pin1-mediated stabilization of MCL1 and promotes GSK3β-mediated degradation of MCL1, leading to activate mitochondria-mediated apoptosis pathway in U937 cells.

Anoxia and glucose supplementation preserve neutrophil viability and function

AbstractFunctional studies of human neutrophils and their transfusion for clinical purposes have been hampered by their short life span after isolation. Here, we demonstrate that neutrophil viability is maintained for 20 hours in culture media at 37°C under anoxic conditions with 3 mM glucose and 32 μg/mL dimethyloxalylglycine supplementation, as evidenced by stabilization of Mcl-1, proliferating cell nuclear antigen (PCNA), and pro-caspase-3. Notably, neutrophil morphology (nucleus shape and cell-surface markers) and functions (phagocytosis, degranulation, calcium release, chemotaxis, and reactive oxygen species production) were comparable to blood circulating neutrophils. The observed extension in neutrophil viability was reversed upon exposure to oxygen. Extending neutrophil life span allowed efficient transfection of plasmids (40% transfection efficiency) and short interfering RNA (interleukin-8, PCNA, and Bax), as a validation of effective and functional genetic manipulation of neutrophils both in vitro and in vivo. In vivo, transfusion of conditioned neutrophils in a neutropenic guinea pig model increased bacterial clearance of Shigella flexneri upon colonic infection, strongly suggesting that these conditioned neutrophils might be suitable for transfusion purposes. In summary, such conditioning of neutrophils in vitro should facilitate their study and offer new opportunities for genetic manipulation and therapeutic use.

Metformin enhances TRAIL-induced apoptosis by Mcl-1 degradation via Mule in colorectal cancer cells.

Metformin is an anti-diabetic drug with a promising anti-cancer potential. In this study, we show that subtoxic doses of metformin effectively sensitize human colorectal cancer (CRC) cells to tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), which induces apoptosis. Metformin alone did not induce apoptosis, but significantly potentiated TRAIL-induced apoptosis in CRC cells. CRC cells treated with metformin and TRAIL showed activation of the intrinsic and extrinsic pathways of caspase activation. We attempted to elucidate the underlying mechanism, and found that metformin significantly reduced the protein levels of myeloid cell leukemia 1 (Mcl-1) in CRC cells and, the overexpression of Mcl-1 inhibited cell death induced by metformin and/or TRAIL. Further experiments revealed that metformin did not affect mRNA levels, but increased proteasomal degradation and protein stability of Mcl-1. Knockdown of Mule triggered a significant decrease of Mcl-1 polyubiquitination. Metformin caused the dissociation of Noxa from Mcl-1, which allowed the binding of the BH3-containing ubiquitin ligase Mule followed by Mcl-1ubiquitination and degradation. The metformin-induced degradation of Mcl-1 required E3 ligase Mule, which is responsible for the polyubiquitination of Mcl-1. Our study is the first report indicating that metformin enhances TRAIL-induced apoptosis through Noxa and favors the interaction between Mcl-1 and Mule, which consequently affects Mcl-1 ubiquitination.

Abstract 4087: Mammary fibroblasts exert divergent effects on the survival of invasive breast cancer cells

Abstract Cancer development and progression are inherently inefficient processes riddled with anti-tumorigenic obstacles. Anoikis, or apoptosis induced by detachment from the extracellular matrix (ECM), represents one prominent hindrance to cancer progression that transformed cells must overcome in order to survive, particularly during the ECM-bereft metastatic cascade. Far from acting in isolation, we report that one mechanisms of anoikis evasion by invasive breast cancer cells involves the exploitation of carcinoma-associated fibroblasts (CAFs) from the surrounding tumor microenvironment. CAFs secrete insulin-like growth factor-binding proteins (IGFBPs) that facilitate non-canonical activation of integrin-linked kinase (ILK), activation of ERK/MAPK, and ultimately stabilization of the anti-apoptotic protein Mcl-1 to promote cancer cell survival during ECM detachment. Further investigation into the influence of the tumor microenvironment on cancer cell survival revealed that, contrary to the role of CAFs, normal mammary fibroblasts (NMFs) appear to exert anti-tumorigenic effects on ECM attached cancer cells. Utilizing conditioned media from NMFs, we have found that NMFs secrete factors that increase caspase activation in multiple cancer cell lines, suggestive of NMF-mediated cancer cell death. Because cancer progression necessitates the intermingling of cancer cells with normal stromal cells, particularly at early time points in primary tumor and metastases formation, we hypothesize that this NMFs pose yet another obstacle to disease progression that may compliment the process of anoikis by capping the metastatic cascade with environments that are inhospitable to cancer cell survival. Similar to anoikis evasion, our data suggests that cancer cells must evade NMF-induced death stimuli in order to survive, possibly through the accrual of CAFs in the tumor microenvironment to combat or replace the pro-apoptotic NMFs. Using traditional and 3D mammalian cell culture in combination with in vivo studies, we aim to delineate the roles of both CAFs and NMFs on cancer cell survival under conditions of differential ECM availability. A more complete understanding of the nuances dictating cancer cell-fibroblast interactions could yield informative data relevant to chemotherapeutic research and development. Citation Format: Kimberly Hagel, Kelsey Weigel, Meaghan Boyd, Luke McCormack, Matthew Champion, Zachary Schafer. Mammary fibroblasts exert divergent effects on the survival of invasive breast cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4087.

Abstract 3497: Metformin enhances TRAIL-induced apoptosis by Mcl-1 degradation via Mule in colorectal cancer cells

Abstract Recent studies have reported that metformin is an anti-diabetic drug, and is the potential a promising anti-cancer agent. The purpose of this study is to evaluate whether metformin effectively sensitize human colorectal cancer (CRC) cells to tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. Metformin alone did not induce apoptosis, but significantly potentiated TRAIL-induced apoptosis in CRC cells. CRC cells treated with metformin and TRAIL activated the intrinsic and extrinsic pathways of caspase activation. To elucidate the underlying mechanism, we found that metformin significantly reduced the protein levels of Mcl-1 (Myeloid cell leukemia 1) in CRC cells, and overexpression of Mcl-1 attenuated the cell death by metformin alone, or in combination with TRAIL. Further experiments revealed that metformin did not affect the mRNA level, but proteasomal degradation and protein stability of Mcl-1. The metformin-induced degradation of Mcl-1 required the E3 ligase Mule, which is responsible for the polyubiquitination of Mcl-1. Taken together, our study is the first report indicating that metformin enhances TRAIL-induced apoptosis through the degradation of Mcl-1 by the proteasome machinery. Citation Format: Seong Hye Park, Dae-Hee Lee, Jung Lim Kim, Sun Il Lee, Bo Ram Kim, Yoo Jin Na, Suk Young Lee, Hong-Jun Kim, Sung Yup Joung, Sanghee Kang, Sang Cheul Oh. Metformin enhances TRAIL-induced apoptosis by Mcl-1 degradation via Mule in colorectal cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3497.

Loss of PKCδ Induces Prostate Cancer Resistance to Paclitaxel through Activation of Wnt/β-Catenin Pathway and Mcl-1 Accumulation.

Prostate cancer is the leading cause of cancer-related death among men in developed countries. Although castration therapy is initially effective, prostate cancers progress to hormone-refractory disease and in this case taxane-based chemotherapy is widely used. Castration-resistant prostate cancer cells often develop resistance to chemotherapy agents and the search for new therapeutic strategies is necessary. In this article, we demonstrate that PKCδ silencing favors mitotic arrest after paclitaxel treatment in PC3 and LNCaP cells; however, this is associated with resistance to paclitaxel-induced apoptosis. In prostate cancer cells, PKCδ seems to exert a proapoptotic role, acting as a negative regulator of the canonical Wnt/β-catenin pathway. PKCδ silencing induces activation of Wnt/β-catenin pathway and the expression of its target genes, including Aurora kinase A, which is involved in activation of Akt and both factors play a key role in GSK3β inactivation and consequently in the stabilization of β-catenin and antiapoptotic protein Mcl-1. We also show that combined treatments with paclitaxel and Wnt/β-catenin or Akt inhibitors improve the apoptotic response to paclitaxel, even in the absence of PKCδ. Finally, we observe that high Gleason score prostate tumors lose PKCδ expression and this correlates with higher activation of β-catenin, inactivation of GSK3β, and higher levels of Aurora kinase A and Mcl-1 proteins. These findings suggest that targeting Wnt/β-catenin or Akt pathways may increase the efficacy of taxane chemotherapy in advanced human prostate cancers that have lost PKCδ expression. Mol Cancer Ther; 15(7); 1713-25. ©2016 AACR.