Prediction of hormone sensitivity for breast cancers

Identification of direct target genes of miR-7, miR-9, miR-96, and miR-182 in the human breast cancer cell lines MCF-7 and MDA-MB-231

Some microRNAs have carcinogenic or tumor suppressive effects in breast cancer, which is the most common cancer in women worldwide. MiR-7 and miR-9 are tumor suppressor microRNAs, which induce apoptosis and inhibit proliferation in breast cancer cells. Moreover, miR-96 and miR-182 are onco-microRNAs that increase proliferation, migration, and tumorigenesis in breast cancer cells. This study aimed to identify the direct target genes of these four microRNAs in the human breast cancer cell lines MCF-7 and MDA-MB-231. Initially, bioinformatics tools were used to identify the target genes that have binding sites for miR-7, MiR-9, MiR-96, and miR-182 and are also associated with breast cancer. Subsequently, the findings of the bioinformatics analysis relating to the effects of these four microRNAs on the 3'-UTR activity of the potential target genes were confirmed using the dual luciferase assay in MCF-7 and MDA-MB-231 cells co-transfected with the vectors containing 3'-UTR segments of the target genes downstream of a luciferase coding gene and each of the microRNAs. Finally, the effects of microRNAs on the endogenous expression of potential target genes were assessed by the overexpression of each of the four microRNAs in MCF-7 and MDA-MB-231 cells. Respectively, three, three, three, and seven genes were found to have binding sites for miR-7, miR-9, miR-96, and miR-182 and were associated with breast cancer. The results of empirical studies including dual luciferase assays and real-time PCR confirmed that miR-7 regulates the expression of BRCA1 and LASP1; MiR-9 regulates the expression of AR; miR-96 regulates the expression of ABCA1; and miR-182 regulates the expression of NBN, TOX3, and LASP1. Taken together, our results suggest that the tumor suppressive effects of miR-7 may be mediated partly by regulating the expression of BRCA1 as a tumor suppressor gene in breast cancer. In addition, this microRNA and miR-182 may have effects on the nodal-positivity and tumor size of breast carcinoma through the regulation of LASP1. The tumor suppressive functions of miR-9 may be mediated partly by suppressing the expression of AR-an oncogene in breast cancer. Moreover, miR-96 may play an oncogenic role in breast cancer by suppressing the apoptosis through the regulation of ABCA1.

3,3'-Diindolylmethane: A Promising Sensitizer of γ-Irradiation

Purpose. Radiotherapy is an effective treatment modality in the clinical treatment of breast cancer. The present work investigated the effect of 3,3′-diindolylmethane (DIM) on γ-irradiation sensitizing human breast carcinoma. Methods. Cell survival, intracellular ROS levels, cell cycle distribution, cell apoptosis, and expression of proteins related to apoptosis were measured with MTT assays, flow cytometry, and Western blot analysis, respectively. Results. In vitro DIM plus γ-irradiation arrested the activity of G2/M phase cell cycle, increased intracellular ROS level, significantly suppressed PARP (poly ADP-ribose polymerase), and enhanced γ-irradiation-induced apoptosis, thereby inhibiting the proliferation of MCF-7 cells. Conclusion. These data provide a rationale for the use of DIM as a promising sensitizer of γ-irradiation.

Correlation between PDZK1, Cdc37, Akt and breast cancer malignancy: the role of PDZK1 in cell growth through Akt stabilization by increasing and interacting with Cdc37

PDZ domain containing 1 (PDZK1) is a scaffold protein that plays a role in the fate of several proteins. Estrogen can induce PDZK1 gene expression; however, our recent report showed that PDZK1 expression in the breast cancer cell line MCF-7 is indirect and involves insulin-like growth factor (IGF)-1 receptor function. Such a relationship was established in cell culture systems and human breast cancer tissues. Here we show that overexpression of PDZK1 promoted an increase in cyclin D1 and enhanced anchorage-independent growth of MCF-7 cells in the absence of 17β-estradiol, suggesting that PDZK1 harbors oncogenic activity. Indeed, PDKZ1 overexpression enhanced epidermal growth factor receptor (EGFR)-stimulated MEK/ERK1/2 signaling and IGF-induced Akt phosphorylation. PDZK1 appeared to play this role, in part, by stabilizing the integrity of the growth promoting factors Akt, human epidermal growth factor receptor 2 (Her2/Neu) and EGFR. Increased Akt levels occurred via a decrease in the ubiquitination of the kinase. PDZK1 overexpression was associated with resistance to paclitaxel/5-fluorouracil/etoposide only at low concentrations. Although the increased stability of Akt was sensitive to heat shock protein 90 (HSP90) inhibition, increased levels of the cochaperone cell division cycle 37 (Cdc37), as well as its ability to bind PDZK1, appear to play a larger role in kinase stability. Using human tissue microarrays, we show strong positive correlation between PDZK1, Akt and Cdc37 protein levels, and all correlated with human breast malignancy. There were no positive correlations between PDZK1 and Cdc37 at the mRNA levels, confirming our in vitro studies. These results demonstrate a relationship between PDZK1, Akt and Cdc37, and potentially Her2/Neu and EGFR, in breast cancer, representing a new axis that can be targeted therapeutically to reduce the burden of human breast cancer.

Transcriptional regulation prediction of antiestrogen resistance in breast cancer based on RNA polymerase II binding data

Background

Although endocrine therapy impedes estrogen-ER signaling pathway and thus reduces breast cancer mortality, patients remain at continued risk of relapse after tamoxifen or other endocrine therapies. Understanding the mechanisms of endocrine resistance, particularly the role of transcriptional regulation is very important and necessary.

Methods

We propose a two-step workflow based on linear model to investigate the significant differences between MCF7 and OHT cells stimulated by 17β-estradiol (E2) respect to regulatory transcription factors (TFs) and their interactions. We additionally compared predicted regulatory TFs based on RNA polymerase II (PolII) binding quantity data and gene expression data, which were taken from MCF7/MCF7+E2 and OHT/OHT+E2 cell lines following the same analysis workflow. Enrichment analysis concerning diseases and cell functions and regulatory pattern analysis of different motifs of the same TF also were performed.

Results

The results showed PolII data could provide more information and predict more recognizably important regulatory TFs. Large differences in TF regulatory mode were found between two cell lines. Through verified through GO annotation, enrichment analysis and related literature regarding these TFs, we found some regulatory TFs such as AP-1, C/EBP, FoxA1, GATA1, Oct-1 and NF-κB, maintained OHT cells through molecular interactions or signaling pathways that were different from the surviving MCF7 cells. From TF regulatory interaction network, we identified E2F, E2F-1 and AP-2 as hub-TFs in MCF7 cells; whereas, in addition to E2F and E2F-1, we identified C/EBP and Oct-1 as hub-TFs in OHT cells. Notably, we found the regulatory patterns of different motifs of the same TF were very different from one another sometimes.

Conclusions

We inferred some regulatory TFs, such as AP-1 and NF-κB, cooperated with ER through both genomic action and non-genomic action. The TFs that were involved in both protein-protein interactions and signaling pathways could be one of the key resistant mechanisms of endocrine therapy and thus also could be new treatment targets for endocrine resistance. Our flexible workflow could be integrated into an existing analytical framework and guide biologists to further determine underlying mechanisms in human diseases.

Fulvestrant induces resistance by modulating GPER and CDK6 expression: implication of methyltransferases, deacetylases and the hSWI/SNF chromatin remodelling complex

Background:

Breast cancer is the leading cause of cancer death in women living in the western hemisphere. Despite major advances in first-line endocrine therapy of advanced oestrogen receptor (ER)-positive breast cancer, the frequent recurrence of resistant cancer cells represents a serious obstacle to successful treatment. Understanding the mechanisms leading to acquired resistance, therefore, could pave the way to the development of second-line therapeutics. To this end, we generated an ER-positive breast cancer cell line (MCF-7) with resistance to the therapeutic anti-oestrogen fulvestrant (FUL) and studied the molecular changes involved in resistance.

Methods:

Naive MCF-7 cells were treated with increasing FUL concentrations and the gene expression profile of the resulting FUL-resistant strain (FR.MCF-7) was compared with that of naive cells using GeneChip arrays. After validation by real-time PCR and/or western blotting, selected resistance-associated genes were functionally studied by siRNA-mediated silencing or pharmacological inhibition. Furthermore, general mechanisms causing aberrant gene expression were investigated.

Results:

Fulvestrant resistance was associated with repression of GPER and the overexpression of CDK6, whereas ERBB2, ABCG2, ER and ER-related genes (GREB1, RERG) or genes expressed in resistant breast cancer (BCAR1, BCAR3) did not contribute to resistance. Aberrant GPER and CDK6 expression was most likely caused by modification of DNA methylation and histone acetylation, respectively. Therefore, part of the resistance mechanism was loss of RB1 control. The hSWI/SNF (human SWItch/Sucrose NonFermentable) chromatin remodelling complex, which is tightly linked to nucleosome acetylation and repositioning, was also affected, because as a stress response to FUL treatment-naive cells altered the expression of five subunits within a few hours (BRG1, BAF250A, BAF170, BAF155, BAF47). The aberrant constitutive expression of BAF250A, BAF170 and BAF155 and a deviant stress response of BRG1, BAF170 and BAF47 in FR.MCF-7 cells to FUL treatment accompanied acquired FUL resistance. The regular and aberrant expression profiles of BAF155 correlated directly with that of CDK6 in naive and in FR.MCF-7 cells corroborating the finding that CDK6 overexpression was due to nucleosome alterations.

Conclusion:

The study revealed that FUL resistance is associated with the dysregulation of GPER and CDK6. A mechanism leading to aberrant gene expression was most likely unscheduled chromatin remodelling by hSWI/SNF. Hence, three targets should be conceptually addressed in a second-line adjuvant therapy: the catalytic centre of SWI/SNF (BRG1) to delay the development of FUL resistance, GPER to increase sensitivity to FUL and the reconstitution of the RB1 pathway to overcome resistance.

PDZK1 is a novel factor in breast cancer that is indirectly regulated by estrogen through IGF-1R and promotes estrogen-mediated growth

Although a relationship between PDZK1 expression and estrogen receptor (ER)-α stimulation has been suggested, the nature of such a connection and the function of PDZK1 in breast cancer remain unknown. Human tissue microarrays (cancer tissue: 262 cores; normal tissue: 87 cores) and breast cancer cell lines were used to conduct the study. We show that PDZK1 protein expression is tightly correlated with human breast malignancy, is negatively correlated with age and had no significant correlation with ER-α expression levels. PDZK1 exhibited an exclusive epithelial expression with mostly cytosolic subcellular localization. Additionally, 17β-estradiol induced PDZK1 expression above its basal level more than 24 h after treatment in MCF-7 cells. PDZK1 expression was indirectly regulated by ER-α stimulation, requiring insulinlike growth factor 1 receptor (IGF-1R) expression and function. The molecular link between PDZK1 and IGF-1R was supported by a significant correlation between protein and mRNA levels (r = 0.591, p < 0.001, and r = 0.537, p < 0.001, respectively) of the two factors in two different cohorts of human breast cancer tissues. Interestingly, PDZK1 knockdown in MCF-7 cells blocked ER-dependent growth and reduced c-Myc expression, whereas ectopic expression of PDZK1 enhanced cell proliferation in the presence or absence of 17β-estradiol potentially through an increase in c-Myc expression, suggesting that PDZK1 has oncogenic activity. PDKZ1 also appeared to interact with the Src/ER-α/epidermal growth factor receptor (EGFR) complex, but not with IGF-1R and enhanced EGFR-stimulated MEK/ERK1/2 signaling. Collectively, our results clarify the relationship between ER-α and PDZK1, propose a direct relationship between PDZK1 and IGF-1R, and identify a novel oncogenic activity for PDZK1 in breast cancer.

An induction of microRNA, miR-7 through estrogen treatment in breast carcinoma

Background

Estrogen plays an important role in the development of estrogen-dependent breast carcinoma. Recently, several studies demonstrated a possible involvement of several micro RNAs (miRNAs) in the development of resistance to endocrine therapy in breast cancer patients, but the correlation between estrogen actions and miRNA expression in breast carcinoma still remains largely unknown. Therefore, in this study, we examined the in vitro effects of estrogen upon miRNA expression profiles in breast carcinoma.

Methods

We first screened the miRNA expression profiles induced by 17β-Estradiol (E2) using RT² miRNA PCR Array in the ER-positive breast carcinoma cell line MCF-7. We identified miR-7 as the important miRNA associated with estrogen actions in these cells and further examined the changes of estrogen-dependent EGFR expression by miR-7 in ER-positive or -negative breast carcinoma cell lines including MCF-7. We also evaluated the correlation between miR-7 and EGFR expression in breast carcinoma cells derived from 21 patients using laser capture microdissection combined with quantitative reverse transcriptase-PCR.

Results

Seventeen miRNAs were significantly induced by E2 treatment in the MCF-7 cell line. Among 17 miRNAs induced by estradiol treatment, only miR-7 expression was significantly decreased by subsequent ICI treatment. The expression of miR-7 was up-regulated 2.94-fold by E2 treatment. miR-7 was reported to suppress epidermal growth factor receptor (EGFR) expression in several human malignancies. Transfection of miR-7 significantly suppressed EGFR mRNA levels in MCF-7 cells. Depletion of E2 from cell culture media also increased the expression level of EGFR mRNA in MCF-7 and T-47D cells but not in ER-negative, MDA-MB-231 and SK-BR-3 cells. We also evaluated the status of miR-7 in breast carcinoma tissues, but the correlation between the status of miR-7 and EGFR in carcinoma cells isolated by laser capture microscopy was not detected.

Conclusions

These results suggest that miR-7 may play a role in the development of resistance to endocrine therapy in breast cancer patients through regulating EGFR expression of carcinoma cells.

Saxifragifolin D induces the interplay between apoptosis and autophagy in breast cancer cells through ROS-dependent endoplasmic reticulum stress

Breast cancer is the leading cause of cancer death among females, and novel chemotherapeutic drugs for treating breast cancer are needed urgently. Saxifragifolin D (SD) was isolated by our group from Androsace umbellata which is commonly used to treat solid tumor. In this study, we evaluated its growth inhibitory effect on breast cancer cells and explored the underlying molecular mechanisms. Our results showed that SD inhibited the growth of both MCF-7 and MDA-MB-231 cells significantly. Mechanistic studies demonstrated that SD induced apoptosis through mitochondrial apoptotic pathway. Evidence of SD-induced autophagy included the occurrence of autophagic vacuoles, up-regulation of LC3-II, Beclin1 and Vps34. Inhibition of autophagy by bafilomycin A1 or Beclin1 siRNA pretreatment decreased the ratio of apoptosis, indicating that autophagy induction contributes to apoptosis and is required for the latter. SD was also found to induce endoplasmic reticulum stress, accompanied by ROS production, increase of intracellular calcium and up-regulation of Bip, IRE1α and XBP-1s. Inhibition of endoplasmic reticulum stress by N-acetyl-l-cysteine, tauroursodeoxycholic acid or IRE1α siRNA pretreatment could suppress both apoptosis and autophagy. Besides, increases in CHOP, calnexin, calpain, p-JNK and p-Bcl-2 were followed by subsequent dissociation of Beclin1 from Bcl-2, further suggesting endoplasmic reticulum stress to be the common signaling pathway shared by SD-induced apoptosis and autophagy. In conclusion, SD inhibits breast cancer cell growth and induces interplay between apoptosis and autophagy through ROS-mediated endoplasmic reticulum stress. It will provide molecular bases for developing SD into a drug candidate for the treatment of breast cancer.

Prolylcarboxypeptidase regulates proliferation, autophagy, and resistance to 4-hydroxytamoxifen-induced cytotoxicity in estrogen receptor-positive breast cancer cells

Endocrine therapy with tamoxifen (TAM) significantly improves outcomes for patients with estrogen receptor-positive breast cancer. However, intrinsic (de novo) or acquired resistance to TAM occurs in a significant proportion of treated patients. To identify genes involved in resistance to TAM, we introduced full-length cDNA expression library into estrogen receptor-positive MCF7 cells and exposed them to a cytotoxic dose of 4-hydroxytamoxifen (4OHTAM). Four different library inserts were isolated from surviving clones. Re-introduction of the genes individually into naive MCF7 cells made them resistant to 4OHTAM. Cells overexpressing these genes had an increase in acidic autophagic vacuoles induced by 4OHTAM, suggesting their role in autophagy. One of them, prolylcarboxypeptidase (PRCP), was investigated further. Overexpression of PRCP increased cell proliferation, boosted several established markers of autophagy, including expression of LC3-2, sequestration of monodansylcadaverine, and proteolysis of BSA in an ER-α dependent manner, and increased resistance to 4OHTAM. Conversely, knockdown of endogenous PRCP in MCF7 cells increased cell sensitivity to 4OHTAM and at the same time decreased cell proliferation and expression of LC3-2, sequestration of monodansylcadaverine, and proteolysis of BSA. Inhibition of enzymatic activity of PRCP enhanced 4OHTAM-induced cytotoxicity in MCF7 cells. Cells with acquired resistance to 4OHTAM exhibited increased PRCP activity, although inhibition of PRCP prevented development of 4OHTAM resistance in parental MCF7 cells and restored response to 4OHTAM in MCF7 cells with acquired resistance to 4OHTAM. Thus, we have for the first time identified PRCP as a resistance factor for 4OHTAM resistance in estrogen receptor-positive breast cancer cells.