Estrogen-mediated upregulation of Noxa is associated with cell cycle progression in estrogen receptor-positive breast cancer cells

Homeostasis: apoptosis and cell cycle in normal and pathological prostate

Prostatic diseases such as hyperplasia and cancer are a consequence of glandular aging due to the loss of homeostasis. Glandular homeostasis is guaranteed by the delicate balance between production and cell death. Both cell renewal and apoptosis are part of this delicate balance. We will explore the predictive capacity for biochemical progression, following prostatectomy, of some members of the Bcl-2 family and of proteins involved in cell cycle inhibition in conjunction with established classical markers. The expression of Bcl-2, Bcl-xL, Mcl-1, Bax, Bim, Bad, PUMA, Noxa, p21, p27, Rb and p53 were analyzed by immunochemistry in 86 samples of radical prostatectomy and correlated with each of the markers established clinicopathological tests using statistical tests such as Sperman, Kaplan-Meier curves, unifactorial Cox, and multifactorial. The most relevant results are: (1) Positive correlation between: p27 with clinical T stage; and PUMA with pathological T stage; (2) Negative correlation between: Bcl-2 with clinical T stage, Bcl-xL with survival, Noxa and pRb with Gleason score.Our results suggest that the expression of Bcl-2, Bcl-xL, PUMA, Noxa, p27, and Rb were related to some of the classic markers established to predict biochemical progression after prostatectomy.

The Role of ERBB2/HER2 Tyrosine Kinase Receptor in the Regulation of Cell Death

HER2 (Human Epidermal Growth Factor Receptor 2), also known as ERBB2, CD340, and Neu protooncogene, is a member of the epidermal growth factor receptor (EGRF) family. Members of the ERBB family, including HER2, activate molecular cascades that stimulate proliferation and migration of cancer cells, as well as their resistance to the anticancer therapy. These proteins are often overexpressed and/or mutated in various cancer types and represent promising targets for the anti-cancer therapy. Currently, anti-HER2 drugs have been approved for the treatment of several types of solid tumors. HER2-specific therapy includes monoclonal antibodies and low-molecular weight inhibitors of tyrosine kinase receptors, such as lapatinib, neratinib, and pyrotinib. In addition to the activation of molecular pathways responsible for cell proliferation and survival under stress conditions, HER2 directly regulates programmed cell death. Here, we review the studies focused on the involvement of HER2 in various signaling pathways and its role in the regulation of apoptosis.

Pro-death signaling of cytoprotective heat shock factor 1: upregulation of NOXA leading to apoptosis in heat-sensitive cells

Heat shock can induce either cytoprotective mechanisms or cell death. We found that in certain human and mouse cells, including spermatocytes, activated heat shock factor 1 (HSF1) binds to sequences located in the intron(s) of the PMAIP1 (NOXA) gene and upregulates its expression which induces apoptosis. Such a mode of PMAIP1 activation is not dependent on p53. Therefore, HSF1 not only can activate the expression of genes encoding cytoprotective heat shock proteins, which prevents apoptosis, but it can also positively regulate the proapoptotic PMAIP1 gene, which facilitates cell death. This could be the primary cause of hyperthermia-induced elimination of heat-sensitive cells, yet other pro-death mechanisms might also be involved.

Ursolic acid facilitates apoptosis in rheumatoid arthritis synovial fibroblasts by inducing SP1-mediated Noxa expression and proteasomal degradation of Mcl-1

Rheumatoid arthritis (RA) is characterized by hyperplastic pannus formation mediated by activated synovial fibroblasts (RASFs) that cause joint destruction. We have shown earlier that RASFs exhibit resistance to apoptosis, primarily as a result of enhanced expression of myeloid cell leukemia-1 (Mcl-1). In this study, we discovered that ursolic acid (UA), a plant-derived pentacyclic triterpenoid, selectively induces B-cell lymphoma 2 homology 3-only protein Noxa in human RASFs. We observed that UA-induced Noxa expression was followed by a consequent decrease in Mcl-1 expression in a dose-dependent manner. Subsequent evaluation of the signaling pathways showed that UA-induced Noxa is primarily mediated by the JNK pathway in human RASFs. Chromatin immunoprecipitation (IP) studies into the promoter region of Noxa indicated the role of transcription factor specificity protein 1 in JNK-mediated Noxa expression. Furthermore, the results from IP studies and proximity ligation assays indicated that UA-induced Noxa colocalizes and associates with Mcl-1 to prime it for proteasomal degradation through K48-linked ubiquitination by the selective recruitment of Mcl-1 ubiquitin ligase E3, a homologous to E6-associated protein C terminus domain-containing E3 ubiquitin ligase. These findings unveil a novel mechanism of inducing apoptosis in RASFs and a potential adjunct therapeutic strategy of regulating synovial hyperplasia in RA.-Kim, E. Y., Sudini, K., Singh, A. K., Haque, M., Leaman, D., Khuder, S., Ahmed, S. Ursolic acid facilitates apoptosis in rheumatoid arthritis synovial fibroblasts by inducing SP1-mediated Noxa expression and proteasomal degradation of Mcl-1.

Dependence of p53-deficient cells on the DHX9 DExH-box helicase

DHX9 is a DExH-box helicase family member with key regulatory roles in a broad range of cellular processes. It participates at multiple levels of gene regulation, including DNA replication, transcription, translation, RNA transport, and microRNA processing. It has been implicated in tumorigenesis and recent evidence suggests that it may be a promising chemotherapeutic target. Previous studies have determined that DHX9 suppression elicits an apoptotic or senescence response by activating p53 signaling. Here, we show that DHX9 inhibition can also have deleterious effects in cells lacking functional p53. Loss of DHX9 led to increased cell death in p53-deficient mouse lymphomas and HCT116 human colon cancer cells, and G0/G1 cell cycle arrest in p53-deficient mouse embryonic fibroblasts. Analysis of mRNA levels for p53 transcriptional targets showed that a subset of p53 targets in the p53-null lymphomas and HCT116 cells were activated despite the absence of functional p53. This implies an alternative pathway of DHX9-mediated activation of cell death and cell cycle arrest in p53-deficient cells and supports the feasibility of targeting DHX9 in p53-deficient tumors.

Coamplification of miR-4728 protects HER2-amplified breast cancers from targeted therapy

In HER2-amplified breast cancers, HER2 inhibitors have been very successful as adjuvant therapy but not as monotherapy. Here, we demonstrate that coamplification of a HER2 intronic miRNA causes intrinsic resistance to HER2 inhibitors by indirectly down-regulating the pro-apoptotic NOXA. Importantly, coinhibition with MCL-1 inhibitors overcomes this resistance.

HER2 (ERBB2) amplification is a driving oncogenic event in breast cancer. Clinical trials have consistently shown the benefit of HER2 inhibitors (HER2i) in treating patients with both local and advanced HER2+ breast cancer. Despite this benefit, their efficacy as single agents is limited, unlike the robust responses to other receptor tyrosine kinase inhibitors like EGFR inhibitors in EGFR-mutant lung cancer. Interestingly, the lack of HER2i efficacy occurs despite sufficient intracellular signaling shutdown following HER2i treatment. Exploring possible intrinsic causes for this lack of response, we uncovered remarkably depressed levels of NOXA, an endogenous inhibitor of the antiapoptotic MCL-1, in HER2-amplified breast cancer. Upon investigation of the mechanism leading to low NOXA, we identified a micro-RNA encoded in an intron of HER2, termed miR-4728, that targets the mRNA of the Estrogen Receptor α (ESR1). Reduced ESR1 expression in turn prevents ERα-mediated transcription of NOXA, mitigating apoptosis following treatment with the HER2i lapatinib. Importantly, resistance can be overcome with pharmacological inhibition of MCL-1. More generally, while many cancers like EGFR-mutant lung cancer are driven by activated kinases that when drugged lead to robust monotherapeutic responses, we demonstrate that the efficacy of targeted therapies directed against oncogenes active through focal amplification may be mitigated by coamplified genes.

Estrogen receptor alpha (ERα/ESR1) mediates the p53-independent overexpression of MDM4/MDMX and MDM2 in human breast cancer

MDM2 and MDM4 are heterodimeric, non-redundant oncoproteins that potently inhibit the p53 tumor suppressor protein. MDM2 and MDM4 also enhance the tumorigenicity of breast cancer cells in in vitro and in vivo models and are overexpressed in primary human breast cancers. Prior studies have characterized Estrogen Receptor Alpha (ERα/ESR1) as a regulator of MDM2 expression and an MDM2- and p53-interacting protein. However, similar crosstalk between ERα and MDM4 has not been investigated. Moreover, signaling pathways that mediate the overexpression of MDM4 in human breast cancer remain to be elucidated. Using the Cancer Genome Atlas (TCGA) breast invasive carcinoma patient cohort, we have analyzed correlations between ERα status and MDM4 and MDM2 expression in primary, treatment-naïve, invasive breast carcinoma samples. We report that the expression of MDM4 and MDM2 is elevated in primary human breast cancers of luminal A/B subtypes and associates with ERα-positive disease, independently of p53 mutation status. Furthermore, in cell culture models, ERα positively regulates MDM4 and MDM2 expression via p53-independent mechanisms, and these effects can be blocked by the clinically-relevant endocrine therapies fulvestrant and tamoxifen. Additionally, ERα also positively regulates p53 expression. Lastly, we report that endogenous MDM4 negatively regulates ERα expression and forms a protein complex with ERα in breast cancer cell lines and primary human breast tumor tissue. This suggests direct signaling crosstalk and negative feedback loops between ERα and MDM4 expression in breast cancer cells. Collectively, these novel findings implicate ERα as a central component of the p53-MDM2-MDM4 signaling axis in human breast cancer.

The role of Nanog expression in tamoxifen-resistant breast cancer cells

There is an accumulation of evidence that shows a significant role of cancer stem cells in tumor initiation, proliferation, relapse, and metastasis. Nanog is the most important core transcription marker of stem cells, known by its role in maintaining pluripotency, proliferation, and differentiation. Therefore, this study aimed to examine the role of Nanog in breast cancer cell tamoxifen resistance and its implications in breast cancer treatment. In this study, the expression of the three core transcription markers Nanog, Oct3/4, and Sox2 were quantitatively evaluated using flow cytometry. Then, small interfering RNA (siRNA) against human Nanog was transfected into tamoxifen-resistant breast cancer cells via Lipofectamine 2000. Nanog gene expression in the cells was detected using reverse transcription polymerase chain reaction (RT-PCR). The change in cell proliferation was evaluated using the tetrazolium bromide method. An enzyme-linked immunosorbent assay was used to detect apoptosis of the transfected cells alone and in combination with 4-hydroxytamoxifen. The results showed a high level expression of Nanog, Oct3/4, and Sox2 in MDA-MB-231 and MCF7/tamoxifen resistant cells compared with MCF7/wild-type. siRNA-mediated Nanog gene silencing can efficiently inhibit cell proliferation and induce apoptosis of tamoxifen-resistant breast cancer cells. This study provides a basis for further study of the role of Nanog in developing resistance to tamoxifen, its implication in breast cancer management, and as a new strategy to enhance response to endocrine therapy.

Regulation of Noxa-mediated apoptosis in Helicobacter pylori-infected gastric epithelial cells

Helicobacter pylori induces the antiapoptotic protein myeloid cell leukemia 1 (Mcl1) in human gastric epithelial cells (GECs). Apoptosis of oncogenic protein Mcl1-expressing cells is mainly regulated by Noxa-mediated degradation of Mcl1. We wanted to elucidate the status of Noxa in H. pylori-infected GECs. For this, various GECs such as AGS, MKN45, and KATO III were either infected with H. pylori or left uninfected. The effect of infection was examined by immunoblotting, immunoprecipitation, chromatin immunoprecipitation assay, in vitro binding assay, flow cytometry, and confocal microscopy. Infected GECs, surgical samples collected from patients with gastric adenocarcinoma as well as biopsy samples from patients infected with H. pylori showed significant up-regulation of both Mcl1 and Noxa compared with noninfected samples. Coexistence of Mcl1 and Noxa was indicative of an impaired Mcl-Noxa interaction. We proved that Noxa was phosphorylated at Ser(13) residue by JNK in infected GECs, which caused cytoplasmic retention of Noxa. JNK inhibition enhanced Mcl1-Noxa interaction in the mitochondrial fraction of infected cells, whereas overexpression of nonphosphorylatable Noxa resulted in enhanced mitochondria-mediated apoptosis in the infected epithelium. Because phosphorylation-dephosphorylation can regulate the apoptotic function of Noxa, this could be a potential target molecule for future treatment approaches for H. pylori-induced gastric cancer.

Estrogen regulation of anti-apoptotic Bcl-2 family member Mcl-1 expression in breast cancer cells

Estrogen is implicated as an important factor in stimulating breast cancer cell proliferation, and presence of estrogen receptor (ER) is an indication of a good prognosis in breast cancer patients. Mcl-1 is an anti-apoptotic Bcl-2 family member that is often over expressed in breast tumors, correlating with poor survival. In breast cancer, it was been previously shown that epidermal growth factor receptors up-regulate Mcl-1 but the role of estrogen in increasing Mcl-1 expression was unknown. In ERα positive cell lines MCF-7 and ZR-75, estrogen treatment increased Mcl-1 expression at both the protein and mRNA level. In two ERα negative cell lines, SK-BR-3 and MDA-MB-231, estrogen failed to increase in Mcl-1 protein expression. We found that ERα antagonists decreased estrogen mediated Mcl-1 expression at both the protein and mRNA level. Upon knockdown of ERα, Mcl-1 mRNA expression after estrogen treatment was also decreased. We also found that ERα binds to the Mcl-1 promoter at a region upstream of the translation start site containing a half ERE site. Streptavidin-pull down assay showed that both ERα and transcription factor Sp1 bind to this region. These results suggest that estrogen is involved in regulating Mcl-1 expression specifically through a mechanism involving ERα.

Estrogen induces Vav1 expression in human breast cancer cells

Vav1, a guanine nucleotide exchange factor (GEF) for Rho family GTPases, is a hematopoietic protein involved in a variety of cellular events. In recent years, aberrant expression of Vav1 has been reported in non-hematopoietic cancers including human breast cancer. It remains to be answered how Vav1 is expressed and what Vav1 does in its non-resident tissues. In this study, we aimed to explore the mechanism for Vav1 expression in breast cancer cells in correlation with estrogen-ER pathway. We not only verified the ectopic expression of Vav1 in human breast cancer cell lines, but also observed that Vav1 expression was induced by 17β-estradiol (E₂), a typical estrogen receptor (ER) ligand, in ER-positive cell lines. On the other hand, Tamoxifen, a selective estrogen receptor modulator (SERM), and ICI 182,780, an ER antagonist, suppressed the expression of Vav1. The estrogen receptor modulating Vav1 expression was identified to be α form, not β. Furthermore, treatment of E₂ increased the transcription of vav1 gene by enhancing the promoter activity, though there was no recognizable estrogen response element (ERE). Nevertheless, two regions at the vav1 gene promoter were defined to be responsible for E₂-induced activation of vav1 promoter. Chromatin immunoprecipitation (ChIP) and co-immunoprecipitation (Co-IP) analyses suggested that ERα might access to the vav1 promoter via interacting with transcription factors, c-Myb and ELF-1. Consequently, the enhanced expression of Vav1 led to the elevation of Cyclin D1 and the progression of cell cycle. The present study implies that estrogen-ER modulates the transcription and expression of Vav1, which may contribute to the proliferation of cancerous cells.

Mitochondrial and postmitochondrial survival signaling in cancer

Cancer cells are resistant to conventional chemotherapy and radiotherapy, however, the molecular mechanisms of resistance to therapy remain unclear. Cellular survival machinery protects mitochondrial integrity against endogenous or exogenous stresses. Prodeath molecules orchestrate around mitochondria to initiate and execute cell death in cancer, and also play an underappreciated role in survival of cancer cells. Prosurvival mechanisms can operate at mitochondrial and postmitochondrial levels to attenuate core apoptotic death program. It is intriguing to explore how prosurvival and prodeath molecules crosstalk to regulate mitochondrial functions leading to increased cancer cell survival. This review describes some putative survival mechanisms at mitochondria, which may play a role in designing effective agents for cancer prevention and therapy. These survival pathways may also have significance in understanding other human pathophysiological conditions including diabetes, cardiovascular, autoimmune, and neurodegenerative diseases.

BAK and NOXA are critical determinants of mitochondrial apoptosis induced by bortezomib in mesothelioma

Based on promising preclinical efficacy associated with the 20S proteasome inhibitor bortezomib in malignant pleural mesothelioma (MPM), two phase II clinical trials have been initiated (EORTC 08052 and ICORG 05–10). However, the potential mechanisms underlying resistance to this targeted drug in MPM are still unknown. Functional genetic analyses were conducted to determine the key mitochondrial apoptotic regulators required for bortezomib sensitivity and to establish how their dysregulation may confer resistance. The multidomain proapoptotic protein BAK, but not its orthologue BAX, was found to be essential for bortezomib-induced apoptosis in MPM cell lines. Immunohistochemistry was performed on tissues from the ICORG-05 phase II trial and a TMA of archived mesotheliomas. Loss of BAK was found in 39% of specimens and loss of both BAX/BAK in 37% of samples. However, MPM tissues from patients who failed to respond to bortezomib and MPM cell lines selected for resistance to bortezomib conserved BAK expression. In contrast, c-Myc dependent transactivation of NOXA was abrogated in the resistant cell lines. In summary, the block of mitochondrial apoptosis is a limiting factor for achieving efficacy of bortezomib in MPM, and the observed loss of BAK expression or NOXA transactivation may be relevant mechanisms of resistance in the clinic.

SNF5 reexpression in malignant rhabdoid tumors regulates transcription of target genes by recruitment of SWI/SNF complexes and RNAPII to the transcription start site of their promoters

Malignant rhabdoid tumor (MRT), a highly aggressive cancer of young children, displays inactivation or loss of the hSNF5/INI1/SMARCB1 gene, a core subunit of the SWI/SNF chromatin-remodeling complex, in primary tumors and cell lines. We have previously reported that reexpression of hSNF5 in some MRT cell lines causes a G1 arrest via p21(CIP1/WAF1) (p21) mRNA induction in a p53-independent manner. However, the mechanism(s) by which hSNF5 reexpression activates gene transcription remains unclear. We initially searched for other hSNF5 target genes by asking whether hSNF5 loss altered regulation of other consensus p53 target genes. Our studies show that hSNF5 regulates only a subset of p53 target genes, including p21 and NOXA, in MRT cell lines. We also show that hSNF5 reexpression modulates SWI/SNF complex levels at the transcription start site (TSS) at both loci and leads to activation of transcription initiation through recruitment of RNA polymerase II (RNAPII) accompanied by H3K4 and H3K36 modifications. Furthermore, our results show lower NOXA expression in MRT cell lines compared with other human tumor cell lines, suggesting that hSNF5 loss may alter the expression of this important apoptotic gene. Thus, one mechanism for MRT development after hSNF5 loss may rely on reduced chromatin-remodeling activity of the SWI/SNF complex at the TSS of critical gene promoters. Furthermore, because we observe growth inhibition after NOXA expression in MRT cells, the NOXA pathway may provide a novel target with clinical relevancy for treatment of this aggressive disease.

Differential inhibitory potencies and mechanisms of the type I ribosome inactivating protein marmorin on estrogen receptor (ER)-positive and ER-negative breast cancer cells

Breast cancer is the second most common cancer with a high incidence rate worldwide. One of the promising therapeutic approaches on breast cancer is to use the drugs that target the estrogen receptor (ER). In the present investigation, marmorin, a type I ribosome inactivating protein from the mushroom Hypsizigus marmoreus, inhibited the survival of breast cancer in vitro and in vivo. It evinced more potent cytotoxicity toward estrogen receptor (ER)-positive MCF7 breast cancer cells than ER-negative MDA-MB-231 cells. Further study disclosed that marmorin undermined the expression level of estrogen receptor α (ERα) and significantly inhibited the proliferation of MCF7 cells induced by 17β-estradiol. Knockdown of ERα in MCF7 cells significantly attenuated the inhibitory effect of marmorin on proliferation, suggesting that the ERα-mediated pathway was implicated in the suppressive action of marmorin on ER-positive breast cancer cells. Moreover, marmorin induced time-dependent apoptosis in both MCF7 and MDA-MB-231 cells. It brought about G2/M-phase arrest, mitochondrial membrane potential depolarization and caspase-9 activation in MCF7 cells, and to a lesser extent in MDA-MB-231 cells. Marmorin triggered the death receptor apoptotic pathway (e.g. caspase-8 activation) and endoplasmic reticulum stress (ERS, as evidenced by phosphorylation of PERK and IRE1α, cleavage of caspase-12, and up-regulation of CHOP expression) in both MCF7 and MDA-MB-231 cells. In summary, marmorin exhibited inhibitory effect on breast cancer partially via diminution of ERα and apoptotic pathways mediated by mitochondrial, death receptor and ERS. The results advocate that marmorin is a potential candidate for breast cancer therapy.

Downregulation of Noxa by RAF/MEK inhibition counteracts cell death response in mutant B-RAF melanoma cells

FDA approval of new therapies in 2011 has greatly expanded the treatment options for metastatic melanoma. Patients with V600 mutant v-raf murine sarcoma viral oncogene homolog B1 (B-RAF) positive metastatic melanoma are now treated with the RAF inhibitor, vemurafenib (Zelboraf) as a first line therapy. Vemurafenib decreases tumor size by at least 30% in approximately 50% of patients and increases progression-free survival and overall patient survival compared to the previous standard-of-care, dacarbazine. However, some patients treated with vemurafenib fail to show significant tumor shrinkage, and most patients who initially respond to the drug eventually show disease progression. Therefore, there is a clinical need to improve efficacy and prevent resistance to vemurafenib. It has been previously shown that cell death resulting from RAF/mitogen-activated protein kinase kinase (MEK) inhibition is largely dependent on increased expression of pro-apoptotic, Bcl-2 homology domain (BH3)-only proteins, such as Bcl-2-like 11 (Bim-EL) and Bcl-2 modifying factor (Bmf). Here, we show that contrary to expression of Bim-EL and Bmf, the pro-apoptotic, BH3-only protein, phorbol-12-myristate-13-acetate-induced protein 1 (Noxa), is strongly downregulated after RAF/MEK inhibition. This downregulation occurs at both the protein and mRNA level of expression and is associated with the inhibition of cell cycle progression. Restoring expression of Noxa in combination with RAF/MEK inhibition enhances cell death. Co-expression of the pro-survival, B-cell CLL/lymphoma 2 (Bcl-2) family member, myeloid cell leukemia sequence 1 (Mcl-1), with Noxa fully mitigates the enhanced cell death associated with increased Noxa expression. These data indicate that manipulating the Noxa/Mcl-1 axis may enhance the efficacy of RAF/MEK inhibitors.

Bim, a proapoptotic protein, up-regulated via transcription factor E2F1-dependent mechanism, functions as a prosurvival molecule in cancer

Proapoptotic Bcl-2 homology 3-only protein Bim plays an important role in Bax/Bak-mediated cytochrome c release and apoptosis. Here, we provide evidence for a novel prosurvival function of Bim in cancer cells. Bim was constitutively overexpressed in multiple prostate and breast cancer cells as well as in primary tumor cells. Quantitative real time PCR analysis showed that Bim was transcriptionally up-regulated. We have identified eight endogenous E2F1-binding sites on the Bim promoter using in silico analysis. Luciferase assay demonstrated that Bim expression was E2F1-dependent as mutation of the E2F1-binding sites on the Bim promoter inhibited luciferase activities. In support, E2F1 silencing led to the loss of Bim expression in cancer cells. Bim primarily localized to mitochondrial and cytoskeleton-associated fractions. Bim silencing or microinjection of anti-Bim antibodies into the cell cytoplasm resulted in cell rounding, detachment, and subsequent apoptosis. We observed up-regulation of prosurvival proteins Bcl-xL and Mcl-1, which sequester Bim in cancer cells. In addition, a phosphorylated form of Bim was also elevated in cancer cells. These findings suggest that the constitutively overexpressed Bim may function as a prosurvival molecule in epithelial cancer cells, and phosphorylation and association with Bcl-xL/Mcl-1 block its proapoptotic functions.