Docetaxel-resistant Lung Adenocarcinoma Cells Research Articles

Cullin7 induces docetaxel resistance by regulating the protein level of the antiapoptotic protein Survivin in lung adenocarcinoma cells.

Lung adenocarcinoma (LUAD) is the most common subtype of non-small cell lung cancer (NSCLC). Chemotherapy resistance is the main cause of chemotherapy failure. Cullin7 (Cul7) is highly expressed in LUAD and is associated with poor prognosis. Moreover, Cul7 is abnormally overexpressed in docetaxel-resistant LUAD cells. Therefore, further exploration of the role and molecular mechanism of Cul7 in LUAD docetaxel resistance is necessary. We established docetaxel-resistant cell lines (A549DTX and H358DTX cell lines) by exposing cells to gradually increasing concentrations of docetaxel. Cell (A549, A549DTX, H358, and H358DTX cell lines) sensitivity to docetaxel was determined via a 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymmethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) assay. And then quantitative polymerase chain reaction (qPCR) and Western blotting were performed to measure the expression of Cul7 and Survivin in A549, A549DTX, H358, and H358DTX cell lines. Subsequently, we knocked down Cul7 in docetaxel-resistant cells and overexpressed Cul7 in parental cells via lentiviral transduction to further validate the correlation between Cul7 and docetaxel resistance, while exploring the molecular mechanism of docetaxel resistance it caused. Immunofluorescence and immunohistochemical (IHC) staining were also used to evaluate the expression and cellular localization of Cul7. To confirm the effect of Cul7 expression on cell apoptosis, we used flow cytometry to detect the apoptosis rate of A549 and A549DTX cells with the same drug concentration. Cul7 was highly expressed in A549DTX and H358DTX cells. However, when Cul7 expression was knocked down in A549DTX and H358DTX cells, cell sensitivity to docetaxel was significantly increased. In addition, we found that Cul7 was coexpressed with Survivin. Silencing Survivin reversed the docetaxel insensitivity caused by Cul7 overexpression. High expression of Cul7 and Survivin in docetaxel-resistant LUAD cells inhibited the intrinsic apoptosis pathway and promoted cell proliferation. Therefore, the Cul7/Survivin axis may play a role in inducing LUAD docetaxel chemoresistance. Cul7 and Survivin were both highly expressed in docetaxel-resistant LUAD cells. Our results suggest that Cul7 may inhibit apoptosis and promote the proliferation of LUAD cells by increasing the Survivin protein level, which in turn contributes to docetaxel chemoresistance in LUAD.

FOX-A1 contributes to acquisition of chemoresistance in human lung adenocarcinoma via transactivation of SOX5

BackgroundChemoresistance is a major obstacle for the effective treatment of lung adenocarcinoma (LAD). Forkhead box (FOX) proteins have been demonstrated to play critical roles in promoting epithelial-mesenchymal transition (EMT) and chemoresistance. However, whether FOX proteins contribute to the acquisition of EMT and chemoresistance in LAD remains largely unknown. MethodsFOX-A1 expression was measured in LAD cells and tissues by qRT-PCR. The expression levels of EMT markers were detected by western blotting and immunofluorescence assay. The interaction between Sex determining region Y-box protein 5 (SOX5) and FOX-A1 was validated by chromatin immunoprecipitation sequence (ChIP-seq) and Chromatin immunoprecipitation (ChIP) assay. Kaplan-Meier analysis and multivariate Cox regression analysis were performed to analyze the significance of FOX-A1 and SOX5 expression in the prognosis of LAD patients. FindingsFOX-A1 was upregulated in docetaxel-resistant LAD cells. High FOX-A1 expression was closely associated with a worse prognosis. Upregulation of FOX-A1 in LAD samples indicated short progression-free survival (PFS) and overall survival (OS). SOX5 is a new and direct target of FOX-A1 and was positively regulated by FOX-A1 in LAD cell lines. Knockdown of FOX-A1 or SOX5 reversed the chemoresistance of docetaxel-resistant LAD cells by suppressing cell proliferation, migration and EMT progress. InterpretationThese data elucidated an original FOX-A1/SOX5 pathway that represents a promising therapeutic target for chemosensitizing LAD and provides predictive biomarkers for evaluating the efficacy of chemotherapies.

Hsa_circ_0003998 Promotes Chemoresistance via Modulation of miR-326 in Lung Adenocarcinoma Cells.

Circular RNAs (circRNAs) represent a new class of noncoding RNAs that is involved in the development of cancer. However, little is known about their role in chemoresistance. In the present study, we found that hsa_circ_0003998 expression levels in lung adenocarcinoma (LAD) tissues and docetaxel-resistant cell lines (A549/DTX and H1299/DTX) were upregulated. Knockdown of hsa_circ_0003998 decreased chemoresistance, inhibited proliferation, and enhanced apoptosis in docetaxel-resistant LAD cells. Moreover, by using bioinformatics and luciferase reporter assays, we found that miR-326 was a direct target of hsa_circ_0003998. Functional analysis revealed that miR-326 mediated the effect of hsa_circ_0003998 on chemosensitivity. Our findings provide a molecular insight on understanding drug resistance in LAD cells. Therefore, inactivation of hsa_circ_0003998 or activation of miR-326 could be a novel approach for the treatment of LAD.

FOX-A1 Contributes to Acquisition of Chemoresistance in Human Lung Adenocarcinoma via Transactivation of SOX5

Background: Chemoresistance is a major obstacle for the effective treatment of lung adenocarcinoma (LAD). Forkhead box (FOX) proteins have recently been demonstrated to play critical roles in promoting epithelial-mesenchymal transition (EMT) and chemoresistance; however, it remains largely unknown whether FOX proteins contribute to the acquisition of EMT and chemoresistance in LAD. Methods: FOX-A1 expression were measured in LAD cells and tissues by qRT-PCR. The expression levels of EMT markers were detected by western blotting and immunofluorescence assay. Sex determining region Y-box protein 5 (SOX5) was identified as a novel and direct target of FOX-A1 via chromatin immunoprecipitation sequence (ChIP-seq) and Chromatin immunoprecipitation (ChIP) assay. Kaplan-Meier analysis and multivariate Cox regression analysis were performed to elucidate the significance of FOX-A1 and SOX5 expression in the prognosis of LAD patients. Findings: FOX-A1 was upregulated in docetaxel-resistant LAD cells that had been previously established, exhibited EMT-like characteristics and increased invasion phenotypes. High FOX-A1 expression was closely associated with a worse tumor response and poor prognosis and was significantly correlated with short progression-free survival (PFS) and overall survival (OS). SOX5 was identified as a new and direct target of FOX-A1 and also acted as an independent prognostic factor for poor PFS and OS in LAD patients. Knockdown of FOX-A1 and SOX5 reversed EMT tomesenchymal-epithelial transition (MET), attenuated metastatic characteristics and reversed the chemoresistance of docetaxel-resistant LAD cells. Interpretation: These data elucidate an original FOX-A1/SOX5 pathway that represents a promising therapeutic target for chemosensitizing LAD and provides predictive markers for evaluating the efficacy of chemotherapies. Funding: This work was supported by the National Natural Science Foundation of China (NO.81672928), Financial Grant from the China Postdoctoral Science Foundation (NO. 2018T110466 and NO.2017M621678), National Natural Science Foundation of China (NO.81702048, NO.81572345 and NO.81503528), the Suzhou Science and Technology Bureau project (No. SYS201609) and the Industrial Technology Innovation Project of Suzhou city (No. SYSD2016124). Declaration of Interest: The authors declare that there is no conflict of interest. Ethical Approval: This study was approved by the Review Board of Hospital Ethics Committee of Nanjing General Hospital of Nanjing Military Command (No. 2012-2-12-015, No. 2012-2-13-022, Nanjing General Hospital of Nanjing Military Command, Nanjing University, China) and conducted in accordance with the Declaration of Helsinki, and written informed consent was obtained from all patients before specimen collection.

Long noncoding RNA ROR regulates chemoresistance in docetaxel-resistant lung adenocarcinoma cells via epithelial mesenchymal transition pathway.

Emerging evidence indicates that the dysregulation of long non-coding RNAs (lncRNAs) contributes to the development and progression of lung adenocarcinoma (LAD), however the underlying mechanism of action of lncRNAs remains unclear. It is well known that the effective treatment of cancers has been hindered by drug resistance in the clinical setting. Epithelial-mesenchymal transition (EMT) has been recognized to be involved in acquiring drug resistance, cell migration and invasion properties in several types of cancer. Docetaxel-resistant LAD cells established previously in our lab present chemoresistant and mesenchymal features. Long intergenic non-protein coding RNA, regulator of reprogramming (linc-ROR), was first discovered in induced pluripotent stem cells (iPSCs) and was upregulated in docetaxel-resistant LAD cells. In this study, we tried to make clarification of lincRNA-related mechanisms underlying EMT followed by acquired resistance to chemotherapy in LAD. In order to hit the mark, we made use of multiple methods including microarray analysis, qRT-PCR, western blotting analysis, loss/gain-of-function analysis, luciferase assays, drug sensitivity assays, wound-healing assay and invasion assay. We found that decreased expression of linc-ROR effectively reversed EMT in docetaxel-resistant LAD cells and sensitized them to chemotherapy. The function of linc-ROR exerted in LAD cells depended on the sponging of miR-145, therefore, releasing the miR-145 target FSCN1, and thus contributing to the acquisition of chemoresistance and EMT phenotypes of docetaxel-resistant LAD cells. Our findings revealed that linc-ROR might act as potential therapeutic target to overcome chemotherapy resistance in LAD.

MiRNA-26a Contributes to the Acquisition of Malignant Behaviors of Doctaxel-Resistant Lung Adenocarcinoma Cells through Targeting EZH2

Background/Aims: Accumulating evidence revealed that microRNAs (miRNAs) have been demonstrated as critical molecules in tumor development and progression. MiR-26a, located in a fragile chromosomal region associated with various human cancer, has been reported to be involved in regulating various cellular process, such as proliferation, apoptosis and invasion through targeting multiple oncogene. Docetaxel-mediated chemotherapy has been applied in improving the survival and prognosis of patients with advanced lung adenocarcinoma (LAD). However, chemoresistance remains a major impediment to clinical application of this agent. It has been presented that decreased miR-26a expression lead to cisplatin resistance and promoted growth and migration in human lung cancer. Enhancer of zeste homolog 2 (EZH2) is the target of miR-26a. The present study aimed to investigate the function of miR-26a/EZH2 in the acquisition of malignant behaviors of LAD. Methods: MiR-26a and EZH2 expression levels in the dcetaxel-insensitive groups (n = 19) and the docetaxel-sensitive groups (n = 18) were assessed by qRT-PCR. Colony formation assay, flow cytometric analysis, wound healing assay, cell transwell assays and western blotting were performed to assess the effects of miR-26a on proliferation, apoptosis and epithelial-to-mesenchymal (EMT) phenotypes in docetaxel resistant LAD cells in vitro. Xenograft transplantation, immunohistochemistry, tunel assays and western blotting assays were employed to demonstrate the role of miR-26a in docetaxel resistant LAD cells in vivo. The expression level of EZH2 in docetaxel-resistant LAD cells and corresponding parental cells was detected by qRT-PCR and western blotting. The relationship between miR-26a and EZH2 was confirmed by luciferase reporter assay. And rescue assays were performed to further confirm that miRNA-26a contributes to the acquisition of malignant behaviors of docetaxel-resistant LAD cells through targeting EZH2. Results: MiR-26a was significantly down-regulated in the dcetaxel-insensitive groups (n = 19) compared with the docetaxel-sensitive groups (n = 18) assessed by qRT-PCR. MiR-26a decreased the proliferation, increased the apoptosis rate and reversed EMT to MET of docetaxel-resistant LAD cells both in vivo and vitro. EZH2 was confirmed as target of miR-26a. Rescue assays further verified that the function of miR-26a exerts in docetaxel-resistant LAD cells is through targeting EZH2. Conclusions: Our data revealed that overexpression of miR-26a in docetaxel-resistant LAD cells could decrease the proliferation, increase the apoptosis rate and reverse EMT to MET of docetaxel-resistant LAD cells both in vivo and vitro and such function is partially exerted via downregulating EZH2. MiR-26a/EZH2 signal pathway makes contribute to the malignant phenotype of docetaxel-resistant of LAD cells which indicated that miR-26a exerts pivotal functions in the molecular etiology of chemoresistant lung adenocarcinoma.

Long noncoding RNA CCAT1 acts as an oncogene and promotes chemoresistance in docetaxel-resistant lung adenocarcinoma cells.

Chemoresistance remains one of the major obstacles in clinical treatment of lung adenocarcinoma (LAD). Indeed, docetaxel-resistant LAD cells present chemoresistance and epithelial-to-mesenchymal transition phenotypes. Long non-coding RNAs (lncRNAs) are known to promote tumorigenesis in many cancer types. Here, we showed that the lncRNA colon cancer-associated transcript-1 (CCAT1) was upregulated in docetaxel-resistant LAD cells. Furthermore, downregulation of CCAT1 decreased chemoresistance, inhibited proliferation, enhanced apoptosis and reversed the epithelial-to-mesenchymal transition phenotype of docetaxel-resistant LAD cells. We also found that the oncogenic function of CCAT1 in docetaxel-resistant LAD cells depended on the sponging of let-7c. In turn, the sponging of let-7c by CCAT1 released Bcl-xl (a let-7c target), thereby promoting the acquisition of chemoresistance and epithelial-to-mesenchymal transition phenotypes in docetaxel-resistant LAD cells. Our data reveal a novel pathway underlying chemoresistance and the epithelial-to-mesenchymal transition in docetaxel-resistant LAD cells.

MiR-200b regulates autophagy associated with chemoresistance in human lung adenocarcinoma.

Chemoresistance remains a major clinical problem in combating human lung adenocarcinoma (LAD), and abnormal autophagy is closely associated with this phenomenon. In the present study, an inverse correlation between miR-200b and autophagy-associated gene 12 (ATG12) expressions was observed in docetaxel-resistant (SPC-A1/DTX and H1299/DTX) and sensitive (SPC-A1 and H1299) LAD cells as well as in tissue samples. Further study showed that miR-200b directly targeted ATG12 in LAD. Moreover, miR-200b-dependent ATG12 downregulation inhibited autophagy and enhanced the chemosensitivity of SPC-A1/DTX and H1299/DTX cells both in vivo and in vitro. LAD chemoresistance is therefore closely related to downregulation of miR-200b and the corresponding upregulation of ATG12. These results provide new evidence for the mechanisms governing the microRNA (miRNA)-ATG12 network and their possible contribution to autophagy modulation and LAD chemoresistance.

MicroRNA-451 induces epithelial–mesenchymal transition in docetaxel-resistant lung adenocarcinoma cells by targeting proto-oncogene c-Myc

Epithelial–mesenchymal transition (EMT) has been reported to play a significant role in tumour metastasis as well as chemoresistance. However, the molecular mechanisms involved in chemotherapy-induced EMT are still unclear. MicroRNA (miRNA) expression and functions have been reported to contribute to phenotypic features of tumour cells. To investigate the roles of miRNAs in chemotherapy-induced EMT, we established two docetaxel-resistant lung adenocarcinoma (LAD) cell models (SPC-A1/DTX and H1299/DTX), which display EMT-like properties and gain increased invasion or migration activity. MiR-451 was found to be significantly downregulated in docetaxel-resistant LAD cells, and re-expression of miR-451 could reverse EMT to mesenchymal–epithelial transition (MET) and inhibit invasion and metastasis of docetaxel-resistant LAD cells both in vitro and in vivo. The proto-oncogene c-Myc was identified as a direct and functional target of miR-451, and further researches confirmed that overexpression of c-Myc which induced extracellular-signal-regulated kinase (ERK)-dependent glycogen synthase kinase-3 beta (GSK-3β) inactivation and subsequent snail activation is essential for acquisition of EMT phenotype induced by loss of miR-451. Furthermore, c-Myc was significantly upregulated in docetaxel-non-responding LAD tissues in comparison with docetaxel-responding tissues, and its expression was inversely correlated with miR-451 expression. This study first reported the involvement of miR-451/c-Myc/ERK/GSK-3β signalling axis in the acquisition of EMT phenotype in docetaxel-resistant LAD cells, suggesting that re-expression of miR-451 or targeting c-Myc will be a potential strategy for the treatment of chemoresistant LAD patients.

Histone deacetylase 1/Sp1/microRNA-200b signaling accounts for maintenance of cancer stem-like cells in human lung adenocarcinoma.

The presence of cancer stem-like cells (CSCs) is one of the mechanisms responsible for chemoresistance that has been a major hindrance towards lung adenocarcinoma (LAD) treatment. Recently, we have identified microRNA (miR)-200b as a key regulator of chemoresistance in human docetaxel-resistant LAD cells. However, whether miR-200b has effects on regulating CSCs remains largely unclear and needs to be further elucidated. Here, we showed that miR-200b was significantly downregulated in CD133+/CD326+ cells that exhibited properties of CSCs derived from docetaxel-resistant LAD cells. Also, restoration of miR-200b could inhibit maintenance and reverse chemoresistance of CSCs. Furthermore, suppressor of zeste-12 (Suz-12) was identified as a direct and functional target of miR-200b, and silencing of Suz-12 phenocopied the effects of miR-200b on CSCs. Additionally, overexpression of histone deacetylase (HDAC) 1 was identified as a pivotal mechanism responsible for miR-200b repression in CSCs through a specificity protein (Sp) 1-dependent mechanism, and restoration of miR-200b by HDAC1 repression significantly suppressed CSCs formation and reversed chemoresistance of CSCs by regulating Suz-12-E-cadherin signaling. Also, downregulation of HDAC1 or upregulation of miR-200b reduced the in vivo tumorigenicity of CSCs. Finally, Suz-12 was inversely correlated with miR-200b, positively correlated with HDAC1 and up-regulated in docetaxel-resistant LAD tissues compared with docetaxel-sensitive tissues. Taken together, the HDAC1/miR-200b/Suz-12-E-cadherin signaling might account for maintenance of CSCs and formation of chemoresistant phenotype in docetaxel-resistant LAD cells.

Acquisition of radioresistance in docetaxel-resistant human lung adenocarcinoma cells is linked with dysregulation of miR-451/c-Myc-survivin/rad-51 signaling.

Chemoresistant tumors usually fail to respond to radiotherapy. However, the mechanisms involved in chemo- and radiotherapy cross resistance are not fully understood. Previously, we have identified microRNA (miR)-451 as a tumor suppressor in lung adenocarcinoma (LAD). However, whether miR-451 plays critical roles in chemo- and radiotherapy cross resistance in LAD is unclear. Here, we established two docetaxel-resistant LAD cell models (SPC-A1/DTX and H1299/DTX), and showed that miR-451 was significantly downregulated in docetaxel-resistant LAD cells. Gain - and loss - of - function assays indicated that re-expression of miR-451 could reverse radioresistance of docetaxel-resistant LAD cells both in vitro and in vivo through promoting apoptosis and DNA double-strand breaks (DSBs). The proto-oncogene c-Myc was identified as a direct target of miR-451, and re-expression of miR-451 inhibited survivin and rad-51 expression by reducing the amount of c-Myc protein binding to their promoters. Silencing of c-Myc could phenocopy the effects of miR-451 upregulation, and restoration of c-Myc could partially rescue the effect of miR-451 upregulation on radiosensitivity of docetaxel-resistant LAD cells. Therefore, dysregulation of miR-451/c-Myc-survivin/rad-51 signaling is responsible for radioresistance of docetaxel-resistant LAD cells, and targeting it will be a potential strategy for reversing chemo- and radiotherapy cross resistance of LAD patients.

HDAC 1/4-mediated silencing of microRNA-200b promotes chemoresistance in human lung adenocarcinoma cells.

Chemoresistance is one of the most significant obstacles in lung adenocarcinoma (LAD) treatment, and this process involves genetic and epigenetic dysregulation of chemoresistance-related genes. Previously, we have shown that restoration of microRNA (miR)-200b significantly reverses chemoresistance of human LAD cells by targeting E2F3. However, the molecular mechanisms involved in the silencing of miR-200b are still unclear. Here we showed that histone deacetylase (HDAC) inhibitors could restore the expression of miR-200b and reverse chemoresistant phenotypes of docetaxel-resistant LAD cells. HDAC1/4 repression significantly increased miR-200b expression by upregulating histone-H3 acetylation level at the two miR-200b promoters partially via a Sp1-dependent pathway. Furthermore, silencing of HDAC1/4 suppressed cell proliferation, promoted cell apoptosis, induced G2/M cell cycle arrest and ultimately reversed in vitro and in vivo chemoresistance of docetaxel-resistant LAD cells, at least partially in a miR-200b-dependent manner. HDAC1/4 suppression-induced rescue of miR-200b contributed to downregulation of E2F3, survivin and Aurora-A, and upregulation of cleaved-caspase-3. HDAC1/4 levels in docetaxel-insensitive human LAD tissues, inversely correlated with miR-200b, were upregulated compared with docetaxel-sensitive tissues. Taken together, our findings suggest that the HDAC1/4/Sp1/miR-200b/E2F3 pathway is responsible for chemoresistance of docetaxel-resistant LAD cells.

Epigenetic downregulation of RUNX3 by DNA methylation induces docetaxel chemoresistance in human lung adenocarcinoma cells by activation of the AKT pathway

The RUNX3 gene has been shown to function as a tumor suppressor gene implicated in various cancers, but its association with tumor chemoresistance has not been fully understood. Here, we investigated the effect of epigenetic downregulation of RUNX3 in docetaxel resistance of human lung adenocarcinoma and its possible molecular mechanisms. RUNX3 was found to be downregulated by hypermethylation in docetaxel-resistant lung adenocarcinoma cells. Its overexpression could resensitize cells to docetaxel both in vitro and in vivo by growth inhibition, enhancement of apoptosis and G1 phase arrest. Conversely, knockdown of RUNX3 could lead to the decreased sensitivity of parental human lung adenocarcinoma cells to docetaxel by enhancing proliferative capacity. Furthermore, we showed that overexpression of RUNX3 could inactivate the AKT/GSK3β/β-catenin signaling pathway in the docetaxel-resistant cells. Importantly, co-transfection of RUNX3 and constitutively active Akt1 could reverse the effects of RUNX3 overexpression, while treatment with the MK-2206 (AKT inhibitor) mimicked the effects of RUNX3 overexpression in docetaxel-resistant human lung adenocarcinoma cells. Immunohistochemical analysis revealed that decreased RUNX3 expression was correlated with high expression of Akt1 and decreased sensitivity of patients to docetaxel-based chemotherapy. Taken together, our results suggest that epigenetic downregulation of RUNX3 can induce docetaxel resistance in human lung adenocarcinoma cells by activating AKT signaling and increasing expression of RUNX3 may represent a promising strategy for reversing docetaxel resistance in the future.

Highlights of This Issue

The phosphorylated sphingolipid metabolites sphingosine-1-phosphate (S1P) and ceramide-1-phosphate (C1P) are known to be highly bioactive and at physiologic concentrations may strongly enhance motility and adhesion in human rhabdomyosarcoma (RMS). Schneider and colleagues show that the bioactive effects of these metabolites are much stronger than the effects observed in response to known RMS prometastatic factors such as stromal derived factors-1 (SDF-1) or hepatocyte growth factor/scatter factor (HGF/SF). Moreover, the levels of S1P and C1P increased in several organs after γ-irradiation or chemotherapy, which indicates a treatment-specific induction of an unwanted prometastatic environment. Most importantly, the metastasis of RMS cells in response to S1P was effectively inhibited in vivo with the S1P-specific binder NOX-S93 that is based on a high-affinity Spiegelmer aptamer. Thus, bioactive lipids play a previously underappreciated role in the dissemination of RMS and the unwanted side effects of radio/chemotherapy by induction of a prometastatic microenvironment. Therefore, an antimetastatic treatment with S1P-specific scavenger activity, such as NOX-S93, could become a part of standard radio/chemotherapy.Taxane-based drugs such as docetaxel are frequently used as chemotherapy in cancer. Docetaxel-resistant lung adenocarcinoma (LAD) cells display chemoradiotherapy resistance and mesenchymal features with enhanced invasiveness and motility. Therefore, a better understanding of the nature of chemo- and radiotherapy resistance and the molecular mechanisms that govern chemotherapy-induced epithelial-to-mesenchymal transition (EMT) in LAD will lead to the identification of novel molecular targets. Cui and colleagues used in vitro and in vivo analyses to show that upregulation of the microRNA Let-7c could not only restore the chemo- or radiosensitivity but also promote the reversal of an EMT phenotype in the docetaxel-resistant LAD cells. In contrast, Let-7c inhibition decreased the chemo- or radiosensitivity of parental LAD cells. Additional study identified that Let-7c targets the prosurvival Bcl-2 family member, B-cell lymphoma–extra large (Bcl-xL), and that manipulation of Bcl-xL mimics the effects of altered Let-7c. Thus, Let-7c may emerge as an important biomarker for chemoradiotherapy response and metastasis as well as a potential therapeutic target for human LADs.Therapy for estrogen receptor–positive (ER+) breast cancers with the antagonist tamoxifen is often associated with recurrent disease. Consequently, new targets are needed for the treatment of ER+ breast cancers that become resistant to tamoxifen. Kharbanda and colleagues show that the transmembrane mucin family member subunit MUC1-C oncoprotein confers tamoxifen resistance. Critically, targeting MUC1-C with a peptidomimetic was not only effective alone but was also effective in combination with tamoxifen in tamoxifen-resistant breast cancer cells. In the aggregate, these findings provide an experimental basis for the development of MUC1-C inhibitors for the treatment of breast cancer patients with tamoxifenresistant disease.MED1 is a component of the Mediator complex that bridges gene-specific factors to the basal transcriptional machinery. MED1 is known to be a critical coactivator for the androgen receptor (AR) and other transcription factors expressed in prostate epithelial cells. Jin and colleagues used immunohistochemistry (IHC) to show that MED1 is significantly overexpressed in human prostate cancer tissue and in an Nkx3.1:Pten-mutant mouse model of prostate cancer. Importantly, MED1 overexpression was correlated with elevated cellular proliferation. Further study using immunoblot and IHC assays revealed that hyperactivated ERK and/or PI3K/AKT signaling drive MED1 overexpression via direct phosphorylation. Moreover, ectopic MED1 overexpression in prostate cancer xenografts accelerates tumor growth, and through genomic analyses the expression of novel genes involved in inflammation, proliferation, and survival were altered. These results define MED1 as a key oncogenic target for ERK and PI3K/AKT signaling during prostate tumorigenesis, and as such, may represent a novel biomarker or target for therapeutic intervention.