A feedback loop between BEX2 and ErbB2 mediated by c-Jun signaling in breast cancer

BEX2 is a member of brain expressed X-linked gene family that is differentially expressed in primary breast tumors. We have previously demonstrated that BEX2 expression protects breast cancer cells against mitochondrial apoptosis and G1 cell cycle arrest. In addition, we have shown that BEX2 is a c-Jun target gene and, in turn, regulates the phosphorylation of c-Jun in breast cancer cells. In our study, we investigated BEX2 protein expression in a tissue microarray cohort of 225 breast tissue samples with known clinical, pathological and biomarker information. We observed that BEX2 protein was overexpressed in ～50% of malignant breast tumors compared to only 7% of benign breast samples. Notably, BEX2 positive tumors identified a subset of breast cancers with the overexpression of ErbB2 and phosphorylated c-Jun proteins. Furthermore, using in vitro models, we demonstrated that the mechanism of this association is a functional feedback loop involving ErbB2, c-Jun and BEX2 in breast cancer cells. In this feedback loop, ErbB2 overexpression results in an induction of c-Jun and BEX2 expression. Importantly, ErbB2 induction of BEX2 expression was abrogated by a dominant-negative mutant of c-Jun, suggesting that this effect was mediated through the regulation of c-Jun signaling. In turn, the overexpression of BEX2 led to an increase in both c-Jun-mediated induction of ErbB2 and c-Jun binding to the ErbB2 promoter in MCF-7 cells. Our study suggests that BEX2 protein is overexpressed in approximately half of breast cancers and has a positive feedback loop with ErbB2 mediated by c-Jun signaling in breast cancer cells.     

Overexpression of p65/RelA potentiates curcumin-induced apoptosis in HCT116 human colon cancer cells

Curcumin, the yellow pigment in the spice turmeric, has potent chemopreventive activities that involve diverse molecular pathways. It is widely believed that curcumin pro-apoptotic properties are mediated by downregulation of NF kappa B (NFkappaB). The p65/RelA subunit of NFkappaB may influence cell death, in part by activation of NFkappaB anti-apoptotic target genes including X-linked inhibitor of apoptosis (XIAP), A20, bcl-xL and inhibition of sustained activation of c-Jun N-terminal kinase (JNK). We have shown previously that curcumin inhibits NFkappaB, activates JNK and promotes apoptosis in HCT116 colorectal cancer cells. Here, we show that forced overexpression of p65 does not affect curcumin-induced JNK activation. Indeed, overexpression of p65 enhanced curcumin-mediated apoptosis as assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) assay and poly(ADP-ribose) polymerase (PARP) cleavage. This potentiating effect of p65 upon curcumin-mediated apoptosis was reversed by transfection of cells with an IkappaB super-repressor (DeltaNIkappaB). Curcumin treatment inhibited expression of NFkappaB anti-apoptotic target genes in mock-transfected and in p65-overexpressing HCT116 cells, although expression levels remained higher in the latter. Taken together, these results show that curcumin-mediated activation of JNK or induction of apoptosis does not require inhibition of p65. Furthermore, curcumin/p65 synergy in promotion of apoptosis cannot be attributed to active repression of NFkappaB anti-apoptotic genes.     

BEX2 regulates mitochondrial apoptosis and G1 cell cycle in breast cancer

We have recently demonstrated that BEX2 is differentially expressed in primary breast tumors and BEX2 expression is required for the Nerve Growth factor inhibition of ceramide‐induced apoptosis in breast cancer. In this study we investigate the functional role of BEX2 in the survival and growth of breast cancer cells. We demonstrate that BEX2 downregulation induces mitochondrial apoptosis and sensitizes breast cancer cells to the pro‐apoptotic effects of ceramide, doxorubicin and staurosporine. In addition, BEX2 overexpression protects the breast cancer cells against mitochondrial apoptosis. We show that this effect of BEX2 is mediated through the modulation of Bcl‐2 protein family, which involves the positive regulation of anti‐apoptotic member Bcl‐2 and the negative regulation of pro‐apoptotic members BAD, BAK1 and PUMA. Moreover, our data suggests that BEX2 expression is required for the normal cell cycle progression during G1 in breast cancer cells through the regulation of cyclin D1 and p21. To further support the significance of BEX2 in the pathogenesis of breast cancer we demonstrate that BEX2 overexpression is associated with a higher activation of the Bcl‐2/NF‐κB pathway in primary breast tumors. Furthermore, we show that BEX2 downregulation results in a higher expression and activity of protein phosphatase 2A. The modulation of protein phosphatase 2A, which is also known to mediate the cellular response to ceramide, provides a possible mechanism to explain the BEX2‐mediated cellular effects. This study demonstrates that BEX2 has a significant role in the regulation of mitochondrial apoptosis and G1 cell cycle in breast cancer.     

自噬通过p38/c-Jun信号通路促进乳腺癌细胞对他莫昔芬耐药的研究

目的 探讨自噬在乳腺癌细胞中对他莫昔芬耐药的影响。方法 免疫荧光法计数MCF-7及MCF-7/TAMR中含有自噬体的细胞比例及平均每个细胞中自噬体的个数;蛋白印迹法检测MCF-7和MCF-7/TAMR中p38、c-Jun和LC3表达的差异;逐步法检测当LC3的表达改变时,产生耐药细胞株时间的差异。结果 与MCF-7比较,MCF-7/TAMR中含有自噬体的细胞比例及平均每个细胞中自噬体的个数均明显增多;MCF-7/TAMR中LC3蛋白的表达水平明显增高;在诱导TAM耐药过程中LC3的表达水平与耐药细胞株的产生时间呈负相关。在MCF-7/TAMR中磷酸化的p38和c-Jun表达明显增加。结论 自噬促进乳腺癌细胞对他莫昔芬耐药,通过降低自噬相关蛋白的表达活性能够抑制乳腺癌耐药细胞的产生,这可能成为难治性乳腺癌治疗的新途径。     

NF-kappaB (p65/RelA) as a regulator of TNFalpha-mediated ML-1 cell differentiation.

ML-1 human myeloblastic leukemia cells, suspended in serum-depleted medium, proliferate when the insulin-like growth factor-1 (IGF-1) and transferrin (Tf) are supplied, but differentiate to monocytes when these factors are replaced by the tumor necrosis factor-alpha (TNF-alpha). Induction of differentiation, but not of proliferation, involved the selective activation of diverse members of the NF-kappaB family of proteins. In differentiation-induced cells, NF-kappaB (p65) was translocated from the cytoplasm to the nucleus, whereas NF-kappaB (p75) remained localized to the cytoplasm. In contrast, NF-kappaB (p52) was present in the nuclei of proliferation- as well as of differentiation-induced ML-1 cells. The differentiation-specific translocation of NF-kappaB (p65) from the cytoplasm to the nucleus was mediated by an increase in the level of NIK, the NF-kappaB-inducing kinase which, through phosphorylation of IkappaB kinase alpha (Ikappakalpha), causes a decrease in the level of IkappaBalpha, allowing p65 to move from the cytoplasm to the nucleus. The p52/p65 heterodimer formed in the nucleus, bound specifically to the promoter of the tumor suppressor protein p53, effecting a 25 to 30-fold increase in the level of this protein. As we reported previously (Li et al, Cancer Res 1998; 58: 4282-4287), that increase led to the decreased expression of proliferating cell nuclear antigen (PCNA) and to the loss of proliferation-associated DNA synthesis. The ensuing uncoupling of growth from differentiation was followed by the initiation of the monocyte-specific differentiation program.     

Tumor lactic acidosis suppresses CTL function by inhibition of p38 and JNK/c-Jun activation

Lactic acidosis is common to most solid tumors and has been found to affect infiltrating immune cells. Here we document effector phase inhibition of cytotoxic T cells (CTLs) involving complete blockage of cytokine production and partial impairment of lytic granule exocytosis. Lactic acidosis impaired TCR-triggered phosphorylation of JNK, c-Jun and p38, while not affecting MEK1 and ERK. The select targeting of signaling proteins involved in IFNγ production (JNK/c-Jun, p38) without affecting those jointly used in cytokine regulation and granule exocytosis (MEK1/ERK) explains the observed split effect of lactic acidosis on the CTL responses. CTL inhibition by lactic acidosis showed fast dynamics with immediate onset and reversion. Functional recovery by neutralizing the extracellular pH despite continuous presence of lactate holds promise that CTL activity can be improved in the milieu of solid tumors with appropriate anti-acidosis treatment, thereby increasing the efficacy of adoptive T cell therapy.     

BEX2 is overexpressed in a subset of primary breast cancers and mediates nerve growth factor/nuclear factor-kappaB inhibition of apoptosis in breast cancer cell lines

We have identified a novel subtype of estrogen receptor (ER)-positive breast cancers with improved outcome after tamoxifen treatment and characterized by overexpression of the gene BEX2. BEX2 and its homologue BEX1 have highly correlated expression and are part of a cluster enriched for ER response and apoptosis genes. BEX2 expression is induced after estradiol (E2) treatment with a peak at 3 h, suggesting BEX2 is an estrogen-regulated gene. BEX2 belongs to a family of genes, including BEX1, NGFRAP1 (alias BEX3), BEXL1 (alias BEX4), and NGFRAP1L1 (alias BEX5). Both BEX1 and NGFRAP1 interact with p75NTR and modulate nerve growth factor (NGF) signaling through nuclear factor-kappaB (NF-kappaB) to regulate cell cycle, apoptosis, and differentiation in neural tissues. In breast cancer cells, NGF inhibits C2-induced apoptosis through binding of p75NTR and NF-kappaB activation. Here, we show that BEX2 expression is necessary and sufficient for the NGF-mediated inhibition (through NF-kappaB activation) of C2-induced apoptosis. We also show that BEX2 modulates apoptosis of breast cancer cells in response to E2 (50 nmol/L) and tamoxifen (5 and 10 micromol/L). Furthermore, BEX2 overexpression enhances the antiproliferative effect of tamoxifen at pharmacologic dose (1 micromol/L). These data suggest that a NGF/BEX2/NF-kappaB pathway is involved in regulating apoptosis in breast cancer cells and in modulating response to tamoxifen in primary tumors.     

p95HER2 and breast cancer

A subtype of HER2-positive tumors with distinct biological and clinical features expresses a series of carboxy-terminal fragments collectively known as p95HER2. One of these fragments, named 100- to 115-kDa p95HER2 or 611-CTF, is hyperactive because of its ability to form homodimers maintained by intermolecular disulfide bonds. Despite lacking the majority of the extracellular domain, this HER2 fragment drives breast cancer progression in vivo. The recent availability of specific anti-p95 antibodies has confirmed previous results indicating that the expression of p95HER2 is predictive of poor prognosis and correlates with resistance to the treatment with trastuzumab, a therapeutic antibody directed against the extracellular domain of HER2.     

靶向p65基因的miRNA对人三阴性乳腺癌细胞裸鼠移植瘤生长的抑制作用

背景与目的:三阴性乳腺癌(triple-negative breast cancer,TNBC)是乳腺癌中预后较差的一个亚型,如何防治TNBC的快速生长成为近几年临床研究的热点之一。NF-κB信号通路在肿瘤发生、发展的各个环节中扮演重要角色,有望成为肿瘤基因治疗新的方向。本研究通过建立人TNBC裸鼠移植瘤模型,观察靶向沉默NF-κB p65亚基的微小RNA(microRNA,miRNA)治疗对TNBC裸鼠移植瘤生长及凋亡的影响,并初步探讨其可能的作用机制。方法:建立人TNBC细胞株MDA-MB-231裸鼠移植瘤动物模型,瘤旁注射p65miRNA质粒(p65miRNA组),同时以注射Neg-miRNA质粒和PBS作为Neg-miRNA对照组和空白对照组。监测肿瘤生长变化,测量肿瘤质量。流式细胞术(flow cytometry,FCM)检测肿瘤细胞凋亡的变化。免疫组化法检测肿瘤组织中p65的表达。Western blot法检测肿瘤组织中Bcl-2和Bax蛋白的表达水平。结果:经p65miRNA处理后,裸鼠肿瘤的生长受到明显抑制。FCM结果表明,p65miRNA组肿瘤细胞凋亡率为(31.08±3.52)%,明显高于Neg-miRNA组(5.76±1.02)%和空白对照组(4.29±0.86)%(P<0.05)。此外,p65miRNA组裸鼠肿瘤组织p65和Bcl-2的蛋白表达明显下调,Bax的蛋白表达显著上调。结论:p65miRNA能抑制人TNBC裸鼠皮下移植瘤的生长,且在体内可诱导肿瘤细胞凋亡。     

Correlation of p27 protein expression with HER-2/neu expression in breast cancer

Strong expression of human epidermal growth factor receptor 2 (HER-2)/neu in breast cancer has been associated with poor prognosis. Reduced expression of p27(Kip1), a cyclin-dependent kinase inhibitor, correlates with poor clinical outcome in breast cancer. In this study, we provide a correlation between these two important prognostic markers in patients with breast cancer. Breast tumor screening using immunohistochemistry indicated that downregulation of p27 correlated with HER-2/neu overexpression in studying 11 normal breast tissues and 51 primary breast carcinomas. We found HER-2/neu protein overexpression in 20 (41%) of 49 breast cancers and low p27 protein expression in 47 (92%) of 51 breast cancers. All 20 (100%) of the tumors that overexpressed HER-2/neu had low levels of p27 protein product; this correlation was statistically significant (P = 0.035). Decreasing p27 expression correlated with increasing HER-2/neu activity. Our results suggest that one function of the HER-2/neu product is to downregulate p27 expression in breast cancer. This study may be significant in selecting patients for HER-2/neu antibody therapy in the future. Mol. Carcinog. 30:169--175, 2001.     

Coexpression of HER-2/neu and p53 in breast cancer identifies a subset with an aggressive biopathological profile

AIMS AND BACKGROUND: Amplification/overexpression of HER-2/neu and inactivation of p53 may be reliable parameters for the prognostic assessment of breast carcinomas. Several studies have addressed the prognostic significance of simultaneous expression of these gene abnormalities with controversial results. METHODS: In this study we analyzed the biopathological profile of 45 breast cancers with both HER-2/neu and p53 overexpression and compared their features with those of 45 randomly selected cases negative for these gene products. RESULTS: Tumors with HER-2/neu and p53 coexpression were found in younger patients, were more often multifocal and/or multicentric, were poorly differentiated in 55% of cases and lymph node-positive in 57%, showing a statistically significant difference compared to tumors with neither alteration (11% and 28%, respectively). Moreover, they were prevalently negative for estrogen (71% vs 22%) and progesterone receptors (78% vs 40%) and showed a higher proliferative activity. CONCLUSIONS: Our data demonstrate that the coexpression of p53 and HER-2/neu is an additive effect in terms of genetic instability reflected by both morphological and biological adverse features; patients with such coexpression should be assigned to specific therapeutic and follow-up protocols.     

JNK/SAPK mediates doxorubicin-induced differentiation and apoptosis in MCF-7 breast cancer cells

Pharmacologic induction of cancer cell differentiation has potential in the treatment of breast cancer. Doxorubicin, a widely used anthracycline antibiotic, was previously reported to induce differentiation of MCF-7 breast cancer cells. We demonstrate in this study that inhibition of MCF-7 breast cancer cell growth by low dose doxorubicin (0.01 µg/ml) was accompanied by an increase in cytokeratin 8/18 and milk fat globule membrane protein expression, biomarkers for differentiation of breast cancer, as well as an increase in JNK/SAPK phosphorylation. High dose doxorubicin (10.0 µg/ml) induced apoptosis in these cells. Overexpression of dominant-inhibitory forms of JNK1 and c-Jun blocked both the differentiation and apoptotic effects of doxorubicin. These results suggest that JNK/SAPK pathway signaling plays a prominent role in doxorubicin-induced cell cycle withdrawal, differentiation and control of apoptosis in this cell system. These findings support the possibility that JNK/SAPK pathway activation may be a means of therapeutic intervention in breast cancer.