Modeling breast cancer-associated c-Src and EGFR overexpression in human MECs: c-Src and EGFR cooperatively promote aberrant three-dimensional acinar structure and invasive behavior

EGFR amplification and EGFRvIII predict and participate in TAT-Cx43266-283 antitumor response in preclinical glioblastoma models

BACKGROUND

Glioblastoma (GBM) commonly displays epidermal growth factor receptor (EGFR) alterations (mainly amplification and EGFRvIII) and TAT-Cx43266-283 is a Src-inhibitory peptide with antitumor properties in preclinical GBM models. Given the link between EGFR and Src, the aim of this study was to explore the role of EGFR in the antitumor effects of TAT-Cx43266-283.

METHODS

The effect of TAT-Cx43266-283, temozolomide (TMZ), and erlotinib (EGFR inhibitor) was studied in patient-derived GBM stem cells (GSCs) and murine neural stem cells (NSCs) with and without EGFR alterations, in vitro and in vivo. EGFR alterations were analyzed by western blot and fluorescence in situ hybridization in these cells, and compared with Src activity and survival in GBM samples from The Cancer Genome Atlas.

RESULTS

The effect of TAT-Cx43266-283 correlated with EGFR alterations in a set of patient-derived GSCs and was stronger than that exerted by TMZ and erlotinib. In fact, TAT-Cx43266-283 only affected NSCs with EGFR alterations, but not healthy NSCs. EGFR alterations correlated with Src activity and poor survival in GBM patients. Finally, tumors generated from NSCs with EGFR alterations showed a decrease in growth, invasiveness, and vascularization after treatment with TAT-Cx43266-283, which enhanced the survival of immunocompetent mice.

CONCLUSIONS

Clinically relevant EGFR alterations are predictors of TAT-Cx43266-283 response and part of its mechanism of action, even in TMZ- and erlotinib-resistant GSCs. TAT-Cx43266-283 targets NSCs with GBM-driver mutations, including EGFR alterations, in an immunocompetent GBM model in vivo, suggesting a promising effect on GBM recurrence. Together, this study represents an important step toward the clinical application of TAT-Cx43266-283.

Down regulation of Pinkbar/pAKT and MMP2/MMP9 expression in MDA-MB-231 breast cancer cells as potential targets in cancer therapy by hAMSCs secretome

Breast cancer (BC) is one of the most causes of cancer-related death among women worldwide. Cancer therapy based on stem cells was considered as a novel and promising platform. In present study, we explored the therapeutic effects of human amniotic mesenchymal stromal cells (hAMSCs) through Pinkbar (planar intestinal-and kidney-specific BAR domain protein), pAKT, and matrix metalloproteinases including MMP2, MMP9 on MDA-MB-231 breast cancer cells. To do so, we employed a co-culture system using 6 well plates transwell with a diameter of 0.4 μm pore sized. After 72h hAMSCs-treated MDA-MB-231 breast cancer cells, the expression of Epidermal growth factor receptor (EGFR), and c-Src (a key mediator in EGFR signaling pathway), Pinkbar, pAKT, MMP2, and MMP9 was analyzed by using quantitative real time PCR (qRT-PCR) and western blot methods. Based on using 2D and 3D cell culture models, the significant reduction of tumor cell growth and motility through down regulation of EGFR, c-Src, Pinkbar, pAKT, MMP2, and MMP9 in MDA-MB-231 breast cancer cells was shown. Also, the induction of cellular apoptosis also found. Our finding indicates that the hAMSCS secretome has therapeutic effects on cancer cells. To identify the details of the molecular mechanisms, more experiments will be required.

RNCE: network integration with reciprocal neighbors contextual encoding for multi-modal drug community study on cancer targets

Mining drug targets and mechanisms of action (MoA) for novel anticancer drugs from pharmacogenomic data is a path to enhance the drug discovery efficiency. Recent approaches have successfully attempted to discover targets/MoA by characterizing drug similarities and communities with integrative methods on multi-modal or multi-omics drug information. However, the sparse and imbalanced community size structure of the drug network is seldom considered in recent approaches. Consequently, we developed a novel network integration approach accounting for network structure by a reciprocal nearest neighbor and contextual information encoding (RNCE) approach. In addition, we proposed a tailor-made clustering algorithm to perform drug community detection on drug networks. RNCE and spectral clustering are proved to outperform state-of-the-art approaches in a series of tests, including network similarity tests and community detection tests on two drug databases. The observed improvement of RNCE can contribute to the field of drug discovery and the related multi-modal/multi-omics integrative studies. Availabilityhttps://github.com/WINGHARE/RNCE.

c-Src and EGFR Inhibition in Molecular Cancer Therapy: What Else Can We Improve?

The proto-oncogene c-Src is a non-receptor tyrosine kinase playing a key role in many cellular pathways, including cell survival, migration and proliferation. c-Src de-regulation has been observed in several cancer types, making it an appealing target for drug discovery efforts. Recent evidence emphasizes its crucial role not only in promoting oncogenic traits, but also in the acquisition and maintenance of cancer resistance to various chemotherapeutic or molecular target drugs. c-Src modulates epidermal growth factor receptor (EGFR) activation and amplifies its downstream oncogenic signals. In this review, we report several studies supporting c-Src kinase role in the intricate mechanisms of resistance to EGFR tyrosine kinase inhibitors (TKIs). We further highlighted pre- and clinical progresses of combined treatment strategies made in recent years. Several pre-clinical data have encouraged the use of c-Src inhibitors in combination with EGFR inhibitors. However, clinical trials provided controversial outcomes in some cancer types. Despite c-Src inhibitors showed good tolerability in cancer patients, no incontrovertible and consistent clinical responses were recorded, supporting the idea that a better selection of patients is needed to improve clinical outcome. Currently, the identification of biological markers predictive of therapy response and the accurate molecular screening of cancer patients aimed to gain most clinical benefits become decisive and mandatory.

EHD1 and RUSC2 Control Basal Epidermal Growth Factor Receptor Cell Surface Expression and Recycling

Epidermal growth factor receptor (EGFR) is a prototype receptor tyrosine kinase and an oncoprotein in many solid tumors. Cell surface display of EGFR is essential for cellular responses to its ligands. While postactivation endocytic trafficking of EGFR has been well elucidated, little is known about mechanisms of basal/preactivation surface display of EGFR. Here, we identify a novel role of the endocytic regulator EHD1 and a potential EHD1 partner, RUSC2, in cell surface display of EGFR. EHD1 and RUSC2 colocalize with EGFR in vesicular/tubular structures and at the Golgi compartment. Inducible EHD1 knockdown reduced the cell surface EGFR expression with accumulation at the Golgi compartment, a phenotype rescued by exogenous EHD1. RUSC2 knockdown phenocopied the EHD1 depletion effects. EHD1 or RUSC2 depletion impaired the EGF-induced cell proliferation, demonstrating that the novel, EHD1- and RUSC2-dependent transport of unstimulated EGFR from the Golgi compartment to the cell surface that we describe is functionally important, with implications for physiologic and oncogenic roles of EGFR and targeted cancer therapies.

AGO2 phosphorylation by c-Src kinase promotes tumorigenesis

Numerous studies have reported that c-Src is highly expressed with high tyrosine kinase activity in a variety of tumors. However, it remains unclear whether c-Src contributes to the miRNA pathway. Here, we report that c-Src can interact with and phosphorylate AGO2, a core component of RISC complex, at tyr 393, tyr 529 and tyr749. Mechanistically, it is confirmed that c-Src phosphorylation of AGO2 at tyr393 reduces its binding to DICER, thereby suppressing the maturation of long-loop pre-miR-192. However, the other two phosphorylation sites don’t work on this function. Significantly, Ectopic expression of wild-type AGO2, but not the three tyrosine site mutants, has an obvious tumor-promoting effect in vitro and in vivo, which function could be blocked thoroughly by treatment with c-Src kinase inhibitor, Saracatinib. Our findings identify AGO2 as c-Src target and c-Src phosphorylation of AGO2 may therefore play a potential role during tumor progress.

The homophilic receptor PTPRK selectively dephosphorylates multiple junctional regulators to promote cell-cell adhesion

Cell-cell communication in multicellular organisms depends on the dynamic and reversible phosphorylation of protein tyrosine residues. The receptor-linked protein tyrosine phosphatases (RPTPs) receive cues from the extracellular environment and are well placed to influence cell signaling. However, the direct events downstream of these receptors have been challenging to resolve. We report here that the homophilic receptor PTPRK is stabilized at cell-cell contacts in epithelial cells. By combining interaction studies, quantitative tyrosine phosphoproteomics, proximity labeling and dephosphorylation assays we identify high confidence PTPRK substrates. PTPRK directly and selectively dephosphorylates at least five substrates, including Afadin, PARD3 and δ-catenin family members, which are all important cell-cell adhesion regulators. In line with this, loss of PTPRK phosphatase activity leads to disrupted cell junctions and increased invasive characteristics. Thus, identifying PTPRK substrates provides insight into its downstream signaling and a potential molecular explanation for its proposed tumor suppressor function.

Dasatinib sensitises triple negative breast cancer cells to chemotherapy by targeting breast cancer stem cells

BACKGROUND

Patients with triple negative breast cancer (TNBC) exhibit poor prognosis and are at high risk of tumour relapse, due to the resistance to chemotherapy. These aggressive phenotypes are in part attributed to the presence of breast cancer stem cells (BCSCs). Therefore, targeting BCSCs is a priority to overcoming chemotherapy failure in TNBCs.

METHODS

We generated paclitaxel (pac)-resistant TNBC cells which displayed higher sphere forming potential and percentage of BCSC subpopulations compared to the parental cells. A screen with various kinase inhibitors revealed dasatinib, a Src kinase family inhibitor, as a potent suppressor of BCSC expansion/sphere formation in pac-resistant TNBC cells.

RESULTS

We found dasatinib to block pac-induced BCSC enrichment and Src activation in both parental and pac-resistant TNBC cells. Interestingly, dasatinib induced an epithelial differentiation of the pac-resistant mesenchymal cells, resulting in their enhanced sensitivity to paclitaxel. The combination treatment of dasatinib and paclitaxel not only decreased the BCSCs numbers and their sphere forming capacity but also synergistically reduced cell viability of pac-resistant cells. Preclinical models of breast cancer further demonstrated the efficiency of the dasatinib/paclitaxel combination treatment in inhibiting tumour growth.

CONCLUSIONS

Dasatinib is a promising anti-BCSC drug that could be used in combination with paclitaxel to overcome chemoresistance in TNBC.

Ecto-5'-nucleotidase (CD73) is a potential target of hepatocellular carcinoma

High expression of ecto-5'-nucleotidase (CD73) has been reported in a number of epithelium origin malignancies. Here, we hypothesize that CD73 promotes hepatocellular carcinoma (HCC) growth and metastasis and that the effect is mediated by epithelial growth factor receptor (EGFR). HCC cells with different malignancies and Tissue microarrays of the tumor and peritumoral liver tissues from 30 independent patients were used to examine CD73 and EGFR expression. Then, MTT and Ki67 detection, together with cell adhesion, invasion, and migration assays were used to evaluate the effects of CD73 on cell growth and metastasis. The expression of EGFR in HCC cells was also tested after suppressing or overexpressing CD73. Lastly, tumor tissues from nude mice, which had been injected subcutaneously with HCC cells, were transplanted subcutaneously into CD73^-/- and wild-type (WT) C57 mice. CD73 expression was higher in HCC cells with greater metastatic potentials and tumor tissues compared with low metastatic cells and peritumor tissues. CD73 and EGFR were coexpressed and positively correlated in tumor and peritumor liver tissues in HCC tissue microarrays. Up-regulationof CD73 by plasmid transfection or by pharmacological agents promoted EGFR expression in HCC cells, whereas suppression of CD73 inhibited these effects. The growth of transplanted tumor tissues was dramatically slower in CD73^-/- mice than in WT type mice in the in vivo experiments. CD73 promotes HCC growth and metastasis and upregulated the expression of EGFR in HCC. Thus, CD73 and EGFR are potential targets in the treatment of HCC.

Src Cooperates with Oncogenic Ras in Tumourigenesis via the JNK and PI3K Pathways in Drosophila epithelial Tissue

The Ras oncogene (Rat Sarcoma oncogene, a small GTPase) is a key driver of human cancer, however alone it is insufficient to produce malignancy, due to the induction of cell cycle arrest or senescence. In a Drosophila melanogaster genetic screen for genes that cooperate with oncogenic Ras (bearing the Ras^V12 mutation, or Ras^ACT), we identified the Drosophila Src (Sarcoma virus oncogene) family non-receptor tyrosine protein kinase genes, Src42A and Src64B, as promoting increased hyperplasia in a whole epithelial tissue context in the Drosophila eye. Moreover, overexpression of Src cooperated with Ras^ACT in epithelial cell clones to drive neoplastic tumourigenesis. We found that Src overexpression alone activated the Jun N-terminal Kinase (JNK) signalling pathway to promote actin cytoskeletal and cell polarity defects and drive apoptosis, whereas, in cooperation with Ras^ACT, JNK led to a loss of differentiation and an invasive phenotype. Src + Ras^ACT cooperative tumourigenesis was dependent on JNK as well as Phosphoinositide 3-Kinase (PI3K) signalling, suggesting that targeting these pathways might provide novel therapeutic opportunities in cancers dependent on Src and Ras signalling.

A miR-200c/141-BMI1 autoregulatory loop regulates oncogenic activity of BMI1 in cancer cells

MicroRNAs (miRNAs) are known to function as oncomiRs or tumor suppressors and are important noncoding RNA regulators of oncogenesis. The miR-200c/141 locus on chromosome 12 encodes miR-200c and miR-141, two members of the miR-200 family, which have been shown to function as tumor suppressive miRNAs by targeting multiple oncogenic factors such as polycomb group protein BMI1. Here, we show that BMI1 reciprocally functions as a transcriptional repressor of the miR-200c/141 cluster and that BMI1 inhibitors upregulate expression of miR-200c and miR-141. Our data suggest that BMI1 binds to the miR-200c/141 promoter and regulates it through transcription factor binding motifs E-box 2 and Z-box 1 to repress expression of miR-200c/141 cluster. We also show that PTC-209, a small molecule inhibitor of BMI1 gene expression induces cellular senescence and transcriptionally upregulates expression of miR-200c/141 cluster in breast cancer cells. Furthermore, inhibition of expression of miR-200c or miR-141 overcomes tumor suppressive effects of PTC-209 including induction of cellular senescence and downregulation of breast cancer stem cell phenotype. Therefore, our studies suggest a reciprocal regulation between BMI1 and miR-200c/141 cluster, and that BMI1 inhibitory drugs can further amplify their inhibitory effects on BMI1 via multiple mechanisms including posttranscriptional regulation by upregulating BMI1 targeting miRNAs.

Clinicopathological and prognostic significance of mitogen-activated protein kinases (MAPK) in breast cancers

BACKGROUND

Mitogen-activated protein kinases (MAPKs) are signalling transduction molecules that have different functions and diverse behaviour in cancer. In breast cancer, MAPK is related to oestrogen receptor (ER) and HER2.

METHODS

Protein expression of a large panel of MAPKs (JNK1/2, ERK, p38, C-JUN and ATF2 including phosphorylated forms) were assessed immunohistochemically in a large (n = 1400) and well-characterised breast cancer series prepared as tissue microarray. Moreover, reverse phase protein array was applied to quantify protein expression of MAPKs in six breast cancer cell lines with different phenotypes including HER2-transfected cells.

RESULTS

MAPKs expression was associated with clinicopathological variables characteristic of good prognosis. These associations were most significant in the whole series and in the ER+ subgroup compared to other BC classes. Most of MAPKs showed a positive association with ER, BCL2 and better outcome and were negatively associated with the proliferation marker Ki67 and p53. Association of MAPK with HER2 was mainly seen in the ER- subgroup. Reverse phase protein array confirmed immunohistochemistry results and revealed differential expression of MAPK proteins in ER+ and ER- cell lines.

CONCLUSIONS

MAPKs are associated with good prognosis and their expression is mainly related to ER. Studying a large panel rather than individual biomarkers may provide improved understanding of the pathway.

The cell cycle regulator ecdysoneless cooperates with H-Ras to promote oncogenic transformation of human mammary epithelial cells

The mammalian ortholog of Drosophila ecdysoneless (Ecd) gene product regulates Rb-E2F interaction and is required for cell cycle progression. Ecd is overexpressed in breast cancer and its overexpression predicts shorter survival in patients with ErbB2-positive tumors. Here, we demonstrate Ecd knock down (KD) in human mammary epithelial cells (hMECs) induces growth arrest, similar to the impact of Ecd Knock out (KO) in mouse embryonic fibroblasts. Furthermore, whole-genome mRNA expression analysis of control vs. Ecd KD in hMECs demonstrated that several of the top 40 genes that were down-regulated were E2F target genes. To address the role of Ecd in mammary oncogenesis, we overexpressed Ecd and/or mutant H-Ras in hTERT-immortalized hMECs. Cell cycle analyses revealed hMECs overexpressing Ecd+Ras showed incomplete arrest in G1 phase upon growth factor deprivation, and more rapid cell cycle progression in growth factor-containing medium. Analyses of cell migration, invasion, acinar structures in 3-D Matrigel and anchorage-independent growth demonstrated that Ecd+Ras-overexpressing cells exhibit substantially more dramatic transformed phenotype as compared to cells expressing vector, Ras or Ecd. Under conditions of nutrient deprivation, Ecd+Ras-overexpressing hMECs exhibited better survival, with substantial upregulation of the autophagy marker LC3 both at the mRNA and protein levels. Significantly, while hMECs expressing Ecd or mutant Ras alone did not form tumors in NOD/SCID mice, Ecd+Ras-overexpressing hMECs formed tumors, clearly demonstrating oncogenic cooperation between Ecd and mutant Ras. Collectively, we demonstrate an important co-oncogenic role of Ecd in the progression of mammary oncogenesis through promoting cell survival.

EGF-receptor specificity for phosphotyrosine-primed substrates provides signal integration with Src

Aberrant activation of the EGF receptor (EGFR) contributes to many human cancers by activating the Ras-MAPK pathway and other pathways. EGFR signaling is augmented by Src-family kinases, but the mechanism is poorly understood. Here, we show that human EGFR preferentially phosphorylates peptide substrates that are primed by a prior phosphorylation. Using peptides based on the sequence of the adaptor protein Shc1, we show that Src mediates the priming phosphorylation, thus promoting subsequent phosphorylation by EGFR. Importantly, the doubly phosphorylated Shc1 peptide binds more tightly than singly phosphorylated peptide to the Ras activator Grb2; this binding is a key step in activating the Ras-MAPK pathway. Finally, a crystal structure of EGFR in complex with a primed Shc1 peptide reveals the structural basis for EGFR substrate specificity. These results provide a molecular explanation for the integration of Src and EGFR signaling with downstream effectors such as Ras.

Missing-in-Metastasis regulates cell motility and invasion via PTPδ-mediated changes in SRC activity

MIM (Missing-in-Metastasis), also known as MTSS1 (metastasis suppressor 1), is a scaffold protein that is down-regulated in multiple metastatic cancer cell lines compared with non-metastatic counterparts. MIM regulates cytoskeletal dynamics and actin polymerization, and has been implicated in the control of cell motility and invasion. MIM has also been shown to bind to a receptor PTP (protein tyrosine phosphatase), PTPδ, an interaction that may provide a link between tyrosine-phosphorylation-dependent signalling and metastasis. We used shRNA-mediated gene silencing to investigate the consequences of loss of MIM on the migration and invasion of the MCF10A mammary epithelial cell model of breast cancer. We observed that suppression of MIM by RNAi enhanced migration and invasion of MCF10A cells, effects that were associated with increased levels of PTPδ. Furthermore, analysis of human clinical data indicated that PTPδ was elevated in breast cancer samples when compared with normal tissue. We demonstrated that the SRC protein tyrosine kinase is a direct substrate of PTPδ and, upon suppression of MIM, we observed changes in the phosphorylation status of SRC; in particular, the inhibitory site (Tyr527) was hypophosphorylated, whereas the activating autophosphorylation site (Tyr416) was hyperphosphorylated. Thus the absence of MIM led to PTPδ-mediated activation of SRC. Finally, the SRC inhibitor SU6656 counteracted the effects of MIM suppression on cell motility and invasion. The present study illustrates that both SRC and PTPδ have the potential to be therapeutic targets for metastatic tumours associated with loss of MIM.

MicroRNA-31 is a transcriptional target of histone deacetylase inhibitors and a regulator of cellular senescence

MicroRNAs (miRNAs) have emerged as important regulators of tumorigenesis. Several miRNAs, which can function either as oncomiRs or tumor suppressive miRs are deregulated in cancer cells. The microRNA-31 (miR-31) has been shown to be overexpressed in metastatic breast cancer. It promotes multiple oncogenic phenotypes, including proliferation, motility, and invasion of cancer cells. Using a breast cancer-related miRNA array analysis, we identified miR-31 as a novel target of histone deacetylase inhibitors (HDACi) in breast cancer cells. Specifically, we show that sodium butyrate (NaB) and panobinostat (LBH589), two broad-spectrum HDAC inhibitors up-regulate hsa-miR-31 (miR-31). The up-regulation of miR-31 was accompanied by repression of the polycomb group (PcG) protein BMI1 and induction of cellular senescence. We further show that inhibition of miR-31 overcomes the senescence-inducing effect of HDACi, and restores expression of the PcG protein BMI1. Interestingly, BMI1 also acts as a repressor of miR-31 transcription, suggesting a cross-negative feedback loop between the expression of miR-31 and BMI1. Our data suggest that miR-31 is an important physiological target of HDACi, and that it is an important regulator of senescence relevant to cancer. These studies further suggest that manipulation of miR-31 expression can be used to modulate senescence-related pathological conditions such as cancer, and the aging process.

The mammalian target of rapamycin complex 1 (mTORC1) in breast cancer: the impact of oestrogen receptor and HER2 pathways

The mammalian target of rapamycin complex 1 (mTORC1) is a downstream of the PI3K/Akt pathway which affects cancer development. mTORC1 has many downstream signalling effectors that can enhance different cellular responses. This study aims to investigate the expression of mTORC1 in breast cancer (BC) and correlate it with key clinicopathological and molecular features of BC especially to proteins related to oestrogen receptor (ER) and HER2 pathways in different BC classes. Moreover, mTORC1 expression was assessed in 6 BC cell lines including ER+ and ER- cell lines with and without HER2 transfection. Immunohistochemistry was used to assess the expression of phospho (p) mTORC1 in a large (n = 1300) annotated BC series prepared as tissue microarray. Reverse phase protein array (RPPA) was used to assess its expression in the different BC cell lines. The expression of p-mTORC1 was cytoplasmic with moderate/high expression noted in 44 % of BC. p-mTORC1 expression was associated with clinicopathological variables characteristic of good prognosis. Positive correlation with ER, ER-related proteins AKT, PI3K and luminal differentiation markers were observed in the whole series and in the ER+HER2- subgroup. Association with HER2 was mainly observed in the ER-negative class. RPPA indicated that p-mTORC1 expression was mainly related to ER expression and with better outcome in the Akt positive tumours. p-mTORC1 is associated with good prognostic features. Its expression is related to ER and ER related proteins in addition to AKT and PI3K. Its relation with HER2 expression is mainly seen in the absence of ER expression.

PLK1 inhibition down-regulates polycomb group protein BMI1 via modulation of the miR-200c/141 cluster

The polycomb group protein BMI1 is an important regulator of cancer stem cell (CSC) phenotype and is often overexpressed in cancer cells. Its overexpression leads to increase in CSC fraction and therapy resistance in tumors. BMI1 functions via polycomb repressive complex 1 (PRC1)-mediated gene silencing and also via PRC1-independent transcriptional activities. At present, very little is known about the therapy reagents that can efficiently inhibit BMI1 expression, and the CSC phenotype. Here, we report that the polo-like kinase 1 (PLK1) regulates BMI1 expression, and that its inhibition can efficiently down-regulate BMI1 expression and PRC1 activity, and induce premature senescence in breast cancer cells. We also show that the exogenous BMI1 overexpression mitigates anti-oncogenic effects of PLK1 inhibition and overcomes senescence induction by PLK1 inhibitors. We further show that PLK1 inhibition down-regulates BMI1 by upregulating the miRNA-200c/141 cluster, which encodes miR-200c and miR-141, both of which are known to post-transcriptionally downregulate BMI1 expression. Thus, our data suggest that PLK1 inhibitors can be successfully used to inhibit growth of tumors in which PcG protein BMI1 is overexpressed or the PRC1 activity is deregulated.

Nexus of signaling and endocytosis in oncogenesis driven by non-small cell lung cancer-associated epidermal growth factor receptor mutants

Epidermal growth factor receptor (EGFR) controls a wide range of cellular processes, and aberrant EGFR signaling as a result of receptor overexpression and/or mutation occurs in many types of cancer. Tumor cells in non-small cell lung cancer (NSCLC) patients that harbor EGFR kinase domain mutations exhibit oncogene addiction to mutant EGFR, which confers high sensitivity to tyrosine kinase inhibitors (TKIs). As patients invariably develop resistance to TKIs, it is important to delineate the cell biological basis of mutant EGFR-induced cellular transformation since components of these pathways can serve as alternate therapeutic targets to preempt or overcome resistance. NSCLC-associated EGFR mutants are constitutively-active and induce ligand-independent transformation in nonmalignant cell lines. Emerging data suggest that a number of factors are critical for the mutant EGFR-dependent tumorigenicity, and bypassing the effects of TKIs on these pathways promotes drug resistance. For example, activation of downstream pathways such as Akt, Erk, STAT3 and Src is critical for mutant EGFR-mediated biological processes. It is now well-established that the potency and spatiotemporal features of cellular signaling by receptor tyrosine kinases such as EGFR, as well as the specific pathways activated, is determined by the nature of endocytic traffic pathways through which the active receptors traverse. Recent evidence indicates that NSCLC-associated mutant EGFRs exhibit altered endocytic trafficking and they exhibit reduced Cbl ubiquitin ligase-mediated lysosomal downregulation. More recent work has shown that mutant EGFRs undergo ligand-independent traffic into the endocytic recycling compartment, a behavior that plays a key role in Src pathway activation and oncogenesis. These studies are beginning to delineate the close nexus between signaling and endocytic traffic of EGFR mutants as a key driver of oncogenic processes. Therefore, in this review, we will discuss the links between mutant EGFR signaling and endocytic properties, and introduce potential mechanisms by which altered endocytic properties of mutant EGFRs may alter signaling and vice versa as well as their implications for NSCLC therapy.

Actin filament-associated protein 1 is required for cSrc activity and secretory activation in the lactating mammary gland

Actin filament-associated protein 1 (AFAP1) is an adaptor protein of cSrc that binds to filamentous actin and regulates the activity of this tyrosine kinase to affect changes to the organization of the actin cytoskeleton. In breast and prostate cancer cells, AFAP1 has been shown to regulate cellular responses requiring actin cytoskeletal changes such as adhesion, invadopodia formation and invasion. However, a normal physiologic role for AFAP1 has remained elusive. In this study, we generated an AFAP1 knockout mouse model that establishes a novel physiologic role for AFAP1 in lactation. Specifically, these animals displayed a defect in lactation that resulted in an inability to nurse efficiently. Histologically, the mammary glands of the lactating knockout mice were distinguished by the accumulation of large cytoplasmic lipid droplets in the alveolar epithelial cells. There was a reduction in lipid synthesis and the expression of lipogenic genes without a corresponding reduction in the production of β-casein, a milk protein. Furthermore, these defects were associated with histologic and biochemical signs of precocious involution. This study also demonstrated that AFAP1 responds to prolactin, a lactogenic hormone, by forming a complex with cSrc and becoming tyrosine phosphorylated. Taken together, these observations pointed to a defect in secretory activation. Certain characteristics of this phenotype mirrored the defect in secretory activation in the cSrc knockout mouse, but most importantly, the activity of cSrc in the mammary gland was reduced during early lactation in the AFAP1-null mouse and the localization of active cSrc at the apical surface of luminal epithelial cells during lactation was selectively lost in the absence of AFAP1. These data define, for the first time, the requirement of AFAP1 for the spatial and temporal regulation of cSrc activity in the normal breast, specifically for milk production.

microRNA-141 regulates BMI1 expression and induces senescence in human diploid fibroblasts

Polycomb group protein BMI1 is an important regulator of senescence, aging, and cancer. On one hand, it is overexpressed in cancer cells and is required for self-renewal of stem cells. On the other hand, it is downregulated during senescence and aging. MicroRNAs have emerged as major regulators of almost every gene associated with cancer, aging, and related pathologies. At present, very little is known about the miRNAs that regulate the expression of BMI1. Here, we report that miR-141 posttranscriptionally downregulates BMI1 expression in human diploid fibroblasts (HDFs) via a miR-141 targeting sequence in the 3' untranslated region of BMI1 mRNA. We also show that overexpression of miR-141 induces premature senescence in HDFs via targeting of BMI1 in normal but not in exogenous BMI1-overexpressing HDFs. Induction of premature senescence in HDFs was accompanied by upregulation of p16INK4a, an important downstream target of BMI1 and a major regulator of senescence. Our results suggest that miR-141-based therapies could be developed to treat pathologies where BMI1 is deregulated.

Src mediates cigarette smoke-induced resistance to tyrosine kinase inhibitors in NSCLC cells

The EGF receptor (EGFR) is a proto-oncogene commonly dysregulated in several cancers including non-small cell lung carcinoma (NSCLC) and, thus, is targeted for treatment using tyrosine kinase inhibitors (TKI) such as erlotinib. However, despite the efficacy observed in patients with NSCLC harboring oncogenic variants of the EGFR, general ineffectiveness of TKIs in patients with NSCLC who are current and former smokers necessitates identification of novel mechanisms to overcome this phenomenon. Previously, we showed that NSCLC cells harboring either wild-type (WT) EGFR or oncogenic mutant (MT) L858R EGFR become resistant to the effects of TKIs when exposed to cigarette smoke, evidenced by their autophosphorylation and prolonged downstream signaling. Here, we present Src as a target mediating cigarette smoke-induced resistance to TKIs in both WT EGFR- and L858R MT EGFR-expressing NSCLC cells. First, we show that cigarette smoke exposure of A549 cells leads to time-dependent activation of Src, which then abnormally binds to the WT EGFR causing TKI resistance, contrasting previous observations of constitutive binding between inactive Src and TKI-sensitive L858R MT EGFR. Next, we show that Src inhibition restores TKI sensitivity in cigarette smoke-exposed NSCLC cells, preventing EGFR autophosphorylation in the presence of erlotinib. Furthermore, we show that overexpression of a dominant-negative Src (Y527F/K295R) restores TKI sensitivity to A549 exposed to cigarette smoke. Importantly, the TKI resistance that emerges even in cigarette smoke-exposed L858R EGFR-expressing NSCLC cells could be eliminated with Src inhibition. Together, these findings offer new rationale for using Src inhibitors for treating TKI-resistant NSCLC commonly observed in smokers.

A comprehensive, multi-scale dynamical model of ErbB receptor signal transduction in human mammary epithelial cells

The non-receptor tyrosine kinase Src and receptor tyrosine kinase epidermal growth factor receptor (EGFR/ErbB1) have been established as collaborators in cellular signaling and their combined dysregulation plays key roles in human cancers, including breast cancer. In part due to the complexity of the biochemical network associated with the regulation of these proteins as well as their cellular functions, the role of Src in EGFR regulation remains unclear. Herein we present a new comprehensive, multi-scale dynamical model of ErbB receptor signal transduction in human mammary epithelial cells. This model, constructed manually from published biochemical literature, consists of 245 nodes representing proteins and their post-translational modifications sites, and over 1,000 biochemical interactions. Using computer simulations of the model, we find it is able to reproduce a number of cellular phenomena. Furthermore, the model predicts that overexpression of Src results in increased endocytosis of EGFR in the absence/low amount of the epidermal growth factor (EGF). Our subsequent laboratory experiments also suggest increased internalization of EGFR upon Src overexpression under EGF-deprived conditions, further supporting this model-generated hypothesis.

Biological effects of AL622, a molecule rationally designed to release an EGFR and a c-Src kinase inhibitor

In breast cancer cells expressing c-Src and EGFR, a control of one of the two oncogenes over proliferation and invasion is observed, whereas in others, the synergistic interaction between them is required for tumor progression. With the purpose of developing molecules with the highest probability for blocking the adverse effects of these two oncogenes, we designed AL622, which contains a quinazoline head targeted to EGFR and a linker that bridges it to the PP2-like structure for targeting c-Src. In case the entire molecule would not be capable of blocking c-Src, we designed AL622 to hydrolyze to an intact c-Src-targeting PP2 molecule. After confirming its binary c-Src-EGFR targeting potency of AL622, we analyzed its potency in isogenic NIH3T3 cells transfected with EGFR and HER2 and human breast cancer cells known to be dominated by c-Src function. The results showed that in EGFR/HER-2-driven cells, it was more potent than PP2 and its activity was in the same range as the latter in more c-Src-driven cells. Its ability to block motility and invasion was comparable with that of PP2 and corresponding combinations, indicating that AL622 could be a better antitumor agent in cells where c-Src and/or EGFR play a role.

Analysis of Epithelial Growth Factor-Receptor (EGFR) Phosphorylation in Uterine Smooth Muscle Tumors: Correlation to Mucin-1 and Galectin-3 Expression

Uterine fibroids are the commonest uterine benign tumors. A potential mechanism of malignant transformation from leiomyomas to leiomyosarcomas has been described. Tyrosine phosphorylation is a key mechanism that controls biological functions, such as proliferation and cell differentiation. The aim of the current study was to evaluate the phosphorylation of epithelial growth factor-receptor (EGFR) in normal myometrium, uterine myomas and uterine leiomyosarcomas. Formalin-fixed paraffin-embedded tissue samples from normal myometrium, leiomyomas and leiomyosarcomas were studied. Samples were immunohistochemically (IHC) assessed using the anti-EGFR phosphorylation of Y845 (pEGFR-Y845) and anti-pEGFR-Y1173 phosphorylation-specific antibodies. IHC staining was evaluated using a semiquantitative score. The expression of pEGFR-Y845 was significantly upregulated in leiomyosarcomas (p < 0.001) compared to leiomyomas and normal myometrium. In contrast, pEGFR-Y1173 did not differ significantly between the three groups of the study. Correlation analysis revealed an overall positive correlation between pEGFR Y845 and mucin 1 (MUC1). Further subgroup analysis within the tumoral group (myomas and leiomyosarcomas) revealed an additional negative correlation between pEGFR Y845 and galectin-3 (gal-3) staining. On the contrary no significant correlation was noted within the non-tumoral group. An upregulated EGFR phosphorylation of Y845 in leiomyosarcomas compared to leiomyomas implicates EGFR activation at this special receptor site. Due to these pEGFR-Y845 variations, it can be postulated that MUC1 interacts with it, whereas gal-3 seems to be cleaved from Y845 phosphorylated EGFR. Further research on this field could focus on differences in EGFR pathways as a potentially advantageous diagnostic tool for investigation of benign and malignant signal transduction processes.

TCPTP regulates SFK and STAT3 signaling and is lost in triple-negative breast cancers

Tyrosine phosphorylation-dependent signaling, as mediated by members of the epidermal growth factor receptor (EGFR) family (ErbB1 to -4) of protein tyrosine kinases (PTKs), Src family PTKs (SFKs), and cytokines such as interleukin-6 (IL-6) that signal via signal transducer and activator of transcription 3 (STAT3), is critical to the development and progression of many human breast cancers. EGFR, SFKs, and STAT3 can serve as substrates for the protein tyrosine phosphatase TCPTP (PTPN2). Here we report that TCPTP protein levels are decreased in a subset of breast cancer cell lines in vitro and that TCPTP protein is absent in a large proportion of "triple-negative" primary human breast cancers. Homozygous TCPTP deficiency in murine mammary fat pads in vivo is associated with elevated SFK and STAT3 signaling, whereas TCPTP deficiency in human breast cancer cell lines enhances SFK and STAT3 signaling. On the other hand, TCPTP reconstitution in human breast cancer cell lines severely impaired cell proliferation and suppressed anchorage-independent growth in vitro and xenograft growth in vivo. These studies establish TCPTP's potential to serve as a tumor suppressor in human breast cancer.

Alterations of EGFR, p53 and PTEN that mimic changes found in basal-like breast cancer promote transformation of human mammary epithelial cells

Breast cancer can be classified into different molecular subtypes with varying clinical and pathological characteristics. The basal-like breast cancer subtype represents one of the most aggressive and lethal types of breast cancer, and due to poor mechanistic understanding, it lacks targeted therapy. Many basal-like breast cancer patient samples display alterations of established drivers of cancer development, including elevated expression of EGFR, p53 inactivating mutations and loss of expression of the tumor suppressor PTEN; however, their contribution to human basal-like breast cancer pathogenesis remains ill-defined. Using non-transformed human mammary epithelial cells, we set out to determine whether altering EGFR, p53 and PTEN in different combinations could contribute to basal-like breast cancer progression through transformation of cells. Altering PTEN in combination with either p53 or EGFR in contrast to any of the single alterations caused increased growth of transformed colonies in soft agar. Concomitantly modifying all three genes led to the highest rate of cellular proliferation and the greatest degree of anchorage-independent colony formation. Results from our effort to engineer a model of BBC expressing alterations of EGFR, p53 and PTEN suggest that these changes are cooperative and likely play a causal role in basal-like breast cancer pathogenesis. Consideration should be given to targeting EGFR and restoring p53 and PTEN signaling simultaneously as a strategy for treatment of this subtype of breast cancer.

MUC20 overexpression predicts poor prognosis and enhances EGF-induced malignant phenotypes via activation of the EGFR-STAT3 pathway in endometrial cancer

OBJECTIVE

Mucins play a critical role in the malignancy of various tumors and have been identified as diagnostic markers and as attractive therapeutic targets. However, the role of mucin (MUC) 20 in endometrial cancer (EC) is still unknown.

METHODS

The relationship between MUC20 expression and clinical characteristics of EC was analyzed in 97 EC tumors and 16 normal tissues by immunohistochemistry. Effects of MUC20 on EC cells, HEC-1A and RL95-2, were examined by in vitro cell growth, migration, and invasion assays, as well as in vivo tumor growth in SCID mouse model. Western blotting was performed to analyze signaling pathways modulated by MUC20.

RESULTS

MUC20 expression was significantly higher in EC tumors compared with the normal tissue. High levels of MUC20 expression in EC tumors were correlated with an unfavorable histologic subtype. Furthermore, MUC20 was an independent prognostic factor for poor survival as evaluated by multivariate analyses. Overexpression of MUC20 in EC cells significantly enhanced cell growth, migration, and invasion, as well as tumor growth in vivo. The MUC20-enhanced invasive behavior was significantly blocked by erlotinib, an EGFR inhibitor. Moreover, MUC20 overexpression enhanced EGF-mediated migration and invasion, suggesting a critical role of EGFR in MUC20-mediated effects. We found that MUC20 overexpression could enhance EGF-induced phosphorylation of EGFR and STAT3. Inhibition of the STAT3 activity by its inhibitor Stattic significantly suppressed the MUC20-enhanced invasive behavior.

CONCLUSIONS

MUC20 is novel prognostic factor for EC and its overexpression enhances EGF-triggered invasive behavior through activation of EGFR-STAT3 pathway.

A positive feedback loop regulates the expression of polycomb group protein BMI1 via WNT signaling pathway

Polycomb group protein BMI1 plays an important role in cellular homeostasis by maintaining a balance between proliferation and senescence. It is often overexpressed in cancer cells and is required for self-renewal of stem cells. At present, very little is known about the signaling pathways that regulate the expression of BMI1. Here, we report that BMI1 autoactivates its own promoter via an E-box present in its promoter. We show that BMI1 acts as an activator of the WNT pathway by repressing Dickkopf (DKK) family of WNT inhibitors. BMI1 mediated repression of DKK proteins; in particular, DKK1 led to up-regulation of WNT target c-Myc, which in turn further led to transcriptional autoactivation of BMI1. Thus, a positive feedback loop connected by the WNT signaling pathway regulates BMI1 expression. This positive feedback loop regulating BMI1 expression may be relevant to the role of BMI1 in promoting cancer and maintaining stem cell phenotype.

Disruption of 3D MCF-12A breast cell cultures by estrogens--an in vitro model for ER-mediated changes indicative of hormonal carcinogenesis

Introduction

Estrogens regulate the proliferation of normal and neoplastic breast epithelium. Although the intracellular mechanisms of estrogens in the breast are largely understood, little is known about how they induce changes in the structure of the mammary epithelium, which are characteristic of breast cancer. In vitro three dimensional (3D) cultures of immortalised breast epithelial cells recapitulate features of the breast epithelium in vivo, including formation of growth arrested acini with hollow lumen and basement membrane. This model can also reproduce features of malignant transformation and breast cancer, such as increased cellular proliferation and filling of the lumen. However, a system where a connection between estrogen receptor (ER) activation and disruption of acini formation can be studied to elucidate the role of estrogens is still missing.

Methods/Principal Findings

We describe an in vitro 3D model for breast glandular structure development, using breast epithelial MCF-12A cells cultured in a reconstituted basement membrane matrix. These cells are estrogen receptor (ER)α, ERβ and G-protein coupled estrogen receptor 1 (GPER) competent, allowing the investigation of the effects of estrogens on mammary gland formation and disruption. Under normal conditions, MCF-12A cells formed organised acini, with deposition of basement membrane and hollow lumen. However, treatment with 17β-estradiol, and the exogenous estrogens bisphenol A and propylparaben resulted in deformed acini and filling of the acinar lumen. When these chemicals were combined with ER and GPER inhibitors (ICI 182,780 and G-15, respectively), the deformed acini recovered normal features, such as a spheroid shape, proliferative arrest and luminal clearing, suggesting a role for the ER and GPER in the estrogenic disruption of acinar formation.

Conclusion

This new model offers the opportunity to better understand the role of the ER and GPER in the morphogenesis of breast glandular structure as well as the events implicated in breast cancer initiation and progression.

EGFR Tyrosine 845 Phosphorylation-Dependent Proliferation and Transformation of Breast Cancer Cells Require Activation of p38 MAPK

Phosphorylation of epidermal growth factor receptor (EGFR) on tyrosine 845 by c-Src has been shown to be important for cell proliferation and migration in several model systems. This cross talk between EGFR and Src family kinases (SFKs) is one mechanism for resistance to EGFR inhibitors both in cell models and in the clinic. Here, we show that phosphorylation of tyrosine 845 on EGFR is required for proliferation and transformation using several cell models of breast cancer. Overexpression of EGFR-Y845F or treating cells with the SFK inhibitor dasatinib abrogated tyrosine 845 phosphorylation, yet had little to no effect on other EGFR phosphorylation sites or EGFR kinase activity. Abrogation of Y845 phosphorylation inhibited cell proliferation and transformation, even though extracellular signal-regulated kinase (ERK) and Akt remained active under these conditions. Importantly, cotransfection of mitogen-activated protein kinase (MAPK) kinase 3 and p38 MAPK restored cell proliferation in the absence of EGFR tyrosine 845 phosphorylation. Taken together, these data demonstrate a novel role for p38 MAPK signaling downstream of EGFR tyrosine 845 phosphorylation in the regulation of breast cancer cell proliferation and transformation and implicate SFK inhibitors as a potential therapeutic mechanism for overcoming EGFR tyrosine kinase inhibitor resistance in breast cancer.

Yin Yang 1 plays an essential role in breast cancer and negatively regulates p27

Yin Yang 1 (YY1) is highly expressed in various types of cancers and regulates tumorigenesis through multiple pathways. In the present study, we evaluated YY1 expression levels in breast cancer cell lines, a breast cancer TMA, and two gene arrays. We observed that, compared with normal samples, YY1 is generally overexpressed in breast cancer cells and tissues. In functional studies, depletion of YY1 inhibited the clonogenicity, migration, invasion, and tumor formation of breast cancer cells, but did not affect the clonogenicity of nontumorigenic cells. Conversely, ectopically expressed YY1 enhanced the migration and invasion of nontumorigenic MCF-10A breast cells. In both a monolayer culture condition and a three-dimensional Matrigel system, silenced YY1 expression changed the architecture of breast cancer MCF-7 cells to that resembling MCF-10A cells, whereas ectopically expressed YY1 in MCF-10A cells had the opposite effect. Furthermore, we detected an inverse correlation between YY1 and p27 expression in both breast cancer cells and xenograft tumors with manipulated YY1 expression. Counteracting the changes in p27 expression attenuated the effects of YY1 alterations on these cells. In addition, YY1 promoted p27 ubiquitination and physically interacted with p27. In conclusion, our data suggest that YY1 is an oncogene and identify p27 as a new target of YY1.

Peptide truncation leads to a twist and an unusual increase in affinity for casitas B-lineage lymphoma tyrosine kinase binding domain

We describe truncation and SAR studies to identify a pentapeptide that binds Cbl tyrosine kinase binding domain with a higher affinity than the parental peptide. The pentapeptide has an alternative binding mode that allows occupancy of a previously uncharacterized groove. A peptide library was used to map the binding site and define the interface landscape. Our results suggest that the pentapeptide is an ideal starting point for the development of inhibitors against Cbl driven diseases.

The impact of adhesion peptides within hydrogels on the phenotype and signaling of normal and cancerous mammary epithelial cells

The microenviroment contributes to directing mammary epithelial cell (MEC) development and the progression of breast cancer. Three-dimensional culture models have been used to support formation of structures that display varying degrees of disorganization that parallel the degree of cancer. Synthetic hydrogels were employed to investigate the mechanisms by which specific adhesion signals in the microenvironment directed development. Polyethylene glycol-based hydrogels supported 3D growth of MECs and directed formation of a range of phenotypes that were functions of genotype, and identity and concentration of adhesion peptides RGD and YIGSR. Non-cancerous and cancerous MECs responded differentially to the same adhesion cues and produced variable structural organizations. An analysis of dynamic signaling pathways revealed differential activities of transcription factors within the MAPK and JAK/STAT pathways in response to genotype and adhesion. These results directly implicate adhesion in cancer development and demonstrate that AP1, CREB, STAT1, and STAT3 all contribute to the genotype dependence of cellular response to adhesion peptides. The tools presented in this work could be applied to other systems and connect extracellular cues with intracellular signaling to molecularly dissect tissue development and further biomaterials development.

A block in lineage differentiation of immortal human mammary stem / progenitor cells by ectopically-expressed oncogenes

INTRODUCTION

Emerging evidence suggests a direct role of cancer stem cells (CSCs) in the development of breast cancer. In vitro cellular models that recapitulate properties of CSCs are therefore highly desirable. We have previously shown that normal human mammary epithelial cells (hMECs) immortalized with human telomerase reverse transcriptase (hTERT) possess properties of mammary stem / progenitor cells.

MATERIALS AND METHODS

In the present study, we used this cell system to test the idea that other known hMEC-immortalizing oncogenes (RhoA, HPVE6, HPVE7, p53 mutant, and treatment with γ-radiation), share with hTERT, the ability to maintain mammary stem / progenitor cells.

RESULTS

The results presented here demonstrate that similar to hMECs immortalized with hTERT, all hMEC cell lines immortalized using various oncogenic strategies express stem / progenitor cell markers. Furthermore, analyses using 2D and 3D culture assays demonstrate that all the immortal cell lines retain their ability to self-renew and to differentiate along the luminal lineage. Remarkably, the stem / progenitor cell lines generated using various oncogenic strategies exhibit a block in differentiation along the myoepithelial lineage, a trait that is retained on hTERT-immortalized stem / progenitors. The inability to differentiate along the myoepithelial lineage could be induced by ectopic mutant p53 expression in hTERT-immortalized hMEC.

CONCLUSIONS

Our studies demonstrate that stem / progenitor cell characteristics of hMECs are maintained upon immortalization by using various cancer-relevant oncogenic strategies. Oncogene-immortalized hMECs show a block in their ability to differentiate along the myoepithelial lineage. Abrogation of the myoepithelial differentiation potential by a number of distinct oncogenic insults suggests a potential explanation for the predominance of luminal and rarity of myoepithelial breast cancers.

Continuous requirement of ErbB2 kinase activity for loss of cell polarity and lumen formation in a novel ErbB2/Neu-driven murine cell line model of metastatic breast cancer

Background:

Well over a quarter of human breast cancers are ErbB2-driven and constitute a distinct subtype with substantially poorer prognosis. Yet, there are substantial gaps in our understanding of how ErbB2 tyrosine kinase activity unleashes a coordinated program of cellular and extracellular alterations that culminate in aggressive breast cancers. Cellular models that exhibit ErbB2 kinase dependency and can induce metastatic breast cancer in immune competent hosts are likely to help bridge this gap.

Materials and Methods:

Here, we derived and characterized a cell line model obtained from a transgenic ErbB2/Neu-driven mouse mammary adenocarcinoma.

Results:

The MPPS1 cell line produces metastatic breast cancers when implanted in the mammary fat pads of immune-compromised as well as syngeneic immune-competent hosts. MPPS1 cells maintain high ErbB2 overexpression when propagated in DFCI-1 or related media, and their growth is ErbB2-dependent, as demonstrated by concentration-dependent inhibition of proliferation with the ErbB kinase inhibitor Lapatinib. When grown in 3-dimensional (3-D) culture on Matrigel, MPPS1 cells predominantly form large irregular cystic and solid structures. Remarkably, low concentrations of Lapatinib led to a switch to regular acinar growth on Matrigel. Immunofluorescence staining of control vs. Lapatinib-treated acini for markers of epithelial polarity revealed that inhibition of ErbB2 signaling led to rapid resumption of normal mammary epithelium-like cell polarity.

Conclusions:

The strict dependence of the MPPS1 cell system on ErbB2 signals for proliferation and alterations in cell polarity should allow its use to dissect ErbB2 kinase-dependent signaling pathways that promote loss of cell polarity, a key component of the epithelial mesenchymal transition and aggressiveness of ErbB2-driven breast cancers.

Src family kinases mediate epidermal growth factor receptor signaling from lipid rafts in breast cancer cells

Activation of the epidermal growth factor receptor (EGFR) regulates cellular proliferation, survival, and migration of breast cancer cells. In particular, EGFR recruits signaling proteins to the cell membrane leading to their phosphorylation and activation. However, EGFR also localizes to other cellular structures, including endosomes, mitochondrion, and nuclei. Recently, we demonstrated that lipid raft localization of EGFR in triple-negative breast cancer cell lines promotes EGFR protein-dependent, EGFR kinase-independent activation of Akt. Here, we further define the mechanism by which lipid rafts regulate EGFR signaling to Akt. Specifically, we show that the non-receptor tyrosine kinase c-Src co-localizes and co-associates with EGFR and lipid rafts. Breast cancer cells resistant to treatment with EGFR inhibitors, were also resistant to treatment with Src family kinase (SFK) inhibitors; however, the combination of EGFR and SFK inhibitors synergistically decreases cell viability. We found that this decrease in cell viability observed with EGFR and SFK inhibitor co-treatment correlates with loss of Akt phosphorylation. In addition, we found that in breast cancer cell lines with EGFR and c-Src co-localized to lipid rafts, phospho-inositide 3 kinase (PI3K) was also associated with lipid rafts. Together, the data herein suggest that lipid rafts provide a platform for the interaction of EGFR, c-Src, and PI3K, leading to activation of cellular survival signaling in breast cancer cells.

Functional interactions between Choline kinase α, epidermal growth factor receptor and c-Src in breast cancer cell proliferation

Epidermal growth factor receptor (EGFR) family members and c-Src are co-overexpressed in many cancers. The synergistic effect of EGFR and c-Src has been shown in the tumorigenesis of breast and other cancers. Reported mechanisms of synergy include transcriptional regulation by STAT5b and the regulation of cellular ATP production by mitochondrial protein COX II. Here, we report a new mechanism of EGFR-c-Src synergy through choline kinase α (CHKA). The first enzyme of the phosphatidyl choline production pathway, CHKA, is overexpressed in many cancers, and the product of the enzyme, phosphocholine, is also increased in tumor cells. In this report, we find that CHKA forms a complex with EGFR in a c-Src-dependent manner. Endogenous CHKA and EGFR co-immunoprecipitated from a variety of breast cancer cell lines and immortalized mammary epithelial cells. CHKA interacted with the EGFR kinase domain upon c-Src co-overexpression and was phosphorylated in a c-Src-dependent manner on Y197 and Y333. Overexpression of EGFR and c-Src increased total cellular activity and protein levels of CHKA. Mutation of CHKA Y197 and Y333 reduced complex formation, EGFR-dependent activation of CHKA enzyme activity and epidermal growth factor (EGF)-dependent DNA synthesis. Furthermore, small interfering RNA-mediated knockdown of CHKA in MCF-7 and MCF-10A cells reduced EGF-dependent cell proliferation. Together, these results strongly implicate a new c-Src-dependent link between CHKA and EGFR, which contributes to the regulation of cell proliferation and tumorigenesis.

The polycomb group protein BMI1 is a transcriptional target of HDAC inhibitors

Polycomb group (PcG) proteins are overexpressed in several human malignancies including breast cancer. In particular, aberrant expression of BMI1 and EZH2 has been linked to metastasis and poor prognosis in cancer patients. At present, very little is known about the pharmacological inhibitors of PcG proteins. Here we show that histone deacetylase inhibitors (HDACi) downregulate expression of BMI1. Treatment of MCF10A cells, which are immortal non-transformed breast epithelial cells, and breast cancer cells with HDACi led to decreased expression of BMI1. We further show that downregulation of BMI1 by HDACi results due to the transcriptional downregulation of BMI1 gene. Specifically, we show that primary transcription and promoter activity of BMI1 is suppressed upon treatment with HDACi. Furthermore, downregulation of BMI1 was accompanied by a decrease in histone 2A lysine 119 ubiquitination (H2AK119Ub), which is catalyzed by BMI1 containing polycomb repressive complex 1. HDACi treatment also led to derepression of growth inhibitory genes and putative tumor suppressors, which are known to be silenced by PcG proteins and polycomb repressive complexes (PRCs). In summary, our findings suggest that BMI1 is an important therapy target of HDACi, and that HDACi can be used alone or in combination with other therapies to inhibit growth of tumors that overexpress PcG proteins such as BMI1.

βTrCP regulates BMI1 protein turnover via ubiquitination and degradation

The polycomb group protein BMI1 has been linked to proliferation, senescence, cancer progression and stem cell phenotype. At present, very little is known about its regulation. Here, we report that BMI1 contains a functional recognition motif for the F box protein βTrCP, which regulates ubiquitination and proteasome-mediated degradation of various proteins. We show that overexpression of wild-type βTrCP but not the ΔF mutant of it promotes BMI1 ubiquitination and degradation, and knockdown of βTrCP results in increased expression of BMI1. Furthermore, a mutant of BMI1 with an altered βTrCP recognition motif is much more stable than wild-type BMI1. We also show that wild-type BMI1 but not the mutant BMI1 interacts with βTrCP. Accordingly, compared to wild-type BMI1, mutant protein exhibited increased pro-oncogenic activity. In summary, our findings suggest that βTrCP regulates turnover of BMI1 and its function relevant to oncogenesis, cellular senescence and aging.

Activation of c-Src/HER1/STAT5b and HER1/ERK1/2 signaling pathways and cell migration by hexachlorobenzene in MDA-MB-231 human breast cancer cell line

Hexachlorobenzene (HCB) is a widespread environmental pollutant. It is a dioxin-like compound and a weak ligand of the aryl hydrocarbon receptor (AhR) protein. HCB is a tumor cocarcinogen in rat mammary gland and an inducer of cell proliferation and c-Src kinase activity in MCF-7 breast cancer cells. This study was carried out to investigate HCB action on c-Src and the human epidermal growth factor receptor (HER1) activities and their downstream signaling pathways, Akt, extracellular-signal-regulated kinase (ERK1/2), and signal transducers and activators of transcription (STAT) 5b, as well as on cell migration in a human breast cancer cell line, MDA-MB-231. We also investigated whether the AhR is involved in HCB-induced effects. We have demonstrated that HCB (0.05μM) produces an early increase of Y416-c-Src, Y845-HER1, Y699-STAT5b, and ERK1/2 phosphorylation. Moreover, our results have shown that the pesticide (15 min) activates these pathways in a dose-dependent manner (0.005, 0.05, 0.5, and 5μM). In contrast, HCB does not alter T308-Akt activation. Pretreatment with a specific inhibitor for c-Src (4-amino-5-(4-chlorophenyl)-7-(t-butyl) pyrazolo[3,4-d]pyrimidine [PP2]) prevents Y845-HER1 and Y699-STAT5b phosphorylation. AG1478, a specific HER1 inhibitor, abrogates HCB-induced STAT5b and ERK1/2 activation, whereas 4,7-orthophenanthroline and α-naphthoflavone, two AhR antagonists, prevent HCB-induced STAT5b and ERK1/2 phosphorylation. HCB enhances cell migration evaluated by scratch motility and transwell assays. Pretreatment with PP2, AG1478, and 4,7-orthophenanthroline suppresses HCB-induced cell migration. These results demonstrate that HCB stimulates c-Src/HER1/STAT5b and HER1/ERK1/2 signaling pathways in MDA-MB-231. c-Src, HER1, and AhR are involved in HCB-induced increase in cell migration. The present study makes a significant contribution to the molecular mechanism of action of HCB in mammary carcinogenesis.

Dynamic, large-scale profiling of transcription factor activity from live cells in 3D culture

Background

Extracellular activation of signal transduction pathways and their downstream target transcription factors (TFs) are critical regulators of cellular processes and tissue development. The intracellular signaling network is complex, and techniques that quantify the activities of numerous pathways and connect their activities to the resulting phenotype would identify the signals and mechanisms regulating tissue development. The ability to investigate tissue development should capture the dynamic pathway activity and requires an environment that supports cellular organization into structures that mimic in vivo phenotypes. Taken together, our objective was to develop cellular arrays for dynamic, large-scale quantification of TF activity as cells organized into spherical structures within 3D culture.

Methodology/Principal Findings

TF-specific and normalization reporter constructs were delivered in parallel to a cellular array containing a well-established breast cancer cell line cultured in Matrigel. Bioluminescence imaging provided a rapid, non-invasive, and sensitive method to quantify luciferase levels, and was applied repeatedly on each sample to monitor dynamic activity. Arrays measuring 28 TFs identified up to 19 active, with 13 factors changing significantly over time. Stimulation of cells with β-estradiol or activin A resulted in differential TF activity profiles evolving from initial stimulation of the ligand. Many TFs changed as expected based on previous reports, yet arrays were able to replicate these results in a single experiment. Additionally, arrays identified TFs that had not previously been linked with activin A.

Conclusions/Significance

This system provides a method for large-scale, non-invasive, and dynamic quantification of signaling pathway activity as cells organize into structures. The arrays may find utility for investigating mechanisms regulating normal and abnormal tissue growth, biomaterial design, or as a platform for screening therapeutics.

Drosophila as a tool for personalized medicine: a primer

The goal of personalized medicine is to treat each patient with the best drug: optimal therapeutic benefit with minimal side effects. The genomic revolution is rapidly identifying the genetic contribution to the diseased state as well as its contribution to drug efficacy and toxicity. The ability to perform genome-wide studies has led to an overwhelming number of candidate genes and/or their associated variants; however, understanding which are of therapeutic importance is becoming the greatest unmet need in the personalized medicine field. A related issue is the need to improve our methods of identifying and characterizing therapeutic drugs in the context of the complex genomic landscape of the intact body. Drosophila have proven to be a powerful tool for understanding the basic biological mechanisms of human development. This article will review Drosophila as a whole animal tool for gene and drug discovery. We will examine how Drosophila can be used to both sort through the myriad of hits coming from human genome-wide scans and to dramatically improve the early steps in pharmaceutical drug development.

Synthetic lethal screen of an EGFR-centered network to improve targeted therapies

Intrinsic and acquired cellular resistance factors limit the efficacy of most targeted cancer therapeutics. Synthetic lethal screens in lower eukaryotes suggest that networks of genes closely linked to therapeutic targets would be enriched for determinants of drug resistance. We developed a protein network centered on the epidermal growth factor receptor (EGFR), which is a validated cancer therapeutic target, and used small interfering RNA screening to comparatively probe this network for proteins that regulate the effectiveness of both EGFR-targeted agents and nonspecific cytotoxic agents. We identified subnetworks of proteins influencing resistance, with putative resistance determinants enriched among proteins that interacted with proteins at the core of the network. We found that clinically relevant drugs targeting proteins connected in the EGFR network, such as protein kinase C or Aurora kinase A, or the transcriptional regulator signal transducer and activator of transcription 3 (STAT3), synergized with EGFR antagonists to reduce cell viability and tumor size, suggesting the potential for a direct path to clinical exploitation. Such a focused approach can potentially improve the coherent design of combination cancer therapies.

Paxillin regulates androgen- and epidermal growth factor-induced MAPK signaling and cell proliferation in prostate cancer cells

Although transcriptional effects of androgens have been extensively studied, mechanisms regulating transcription-independent (nongenomic) androgen actions are poorly understood. Previously, we have shown that paxillin, a multidomain adaptor protein, is a critical regulator of testosterone-induced MAPK-signaling during Xenopus oocyte maturation. Here we examine the nongenomic effects of dihydrotestosterone (DHT) in prostate cancer cells, focusing on how paxillin mediates Erk signaling and downstream physiologic actions. We show that in LnCAP cells DHT functions as a growth factor that indirectly activates the EGF-receptor (EGFR) via androgen receptor binding and matrix metalloproteinase-mediated release of EGFR ligands. Interestingly, siRNA-mediated knockdown of paxillin expression in androgen-dependent LnCAP cells as well as in androgen-independent PC3 cells abrogates DHT- and/or EGF-induced Erk signaling. Furthermore, EGFR-induced Erk activation requires Src-mediated phosphorylation of paxillin on tyrosines 31/118. In contrast, paxillin is not required for PKC-induced Erk signaling. However, Erk-mediated phosphorylation of paxillin on serines 83/126/130 is still needed for both EGFR and PKC-mediated cellular proliferation. Thus, paxillin serves as a specific upstream regulator of Erk in response to receptor-tyrosine kinase signaling but as a general regulator of downstream Erk actions regardless of agonist. Importantly, Erk-mediated serine phosphorylation of paxillin is also required for DHT-induced prostate-specific antigen mRNA expression in LnCAP cells as well as EGF-induced cyclin D1 mRNA expression in PC3 cells, suggesting that paxillin may regulate prostate cancer proliferation by serving as a liaison between extra-nuclear kinase signaling and intra-nuclear transcriptional signals. Thus, paxillin may prove to be a novel diagnostic or therapeutic target in prostate cancer.

Deletion analysis of BMI1 oncoprotein identifies its negative regulatory domain

BACKGROUND

The polycomb group (PcG) protein BMI1 is an important regulator of development. Additionally, aberrant expression of BMI1 has been linked to cancer stem cell phenotype and oncogenesis. In particular, its overexpression has been found in several human malignancies including breast cancer. Despite its established role in stem cell maintenance, cancer and development, at present not much is known about the functional domains of BMI1 oncoprotein. In the present study, we carried out a deletion analysis of BMI1 to identify its negative regulatory domain.

RESULTS

We report that deletion of the C-terminal domain of BMI1, which is rich in proline-serine (PS) residues and previously described as PEST-like domain, increased the stability of BMI1, and promoted its pro-oncogenic activities in human mammary epithelial cells (HMECs). Specifically, overexpression of a PS region deleted mutant of BMI1 increased proliferation of HMECs and promoted an epithelial-mesenchymal transition (EMT) phenotype in the HMECs. Furthermore, when compared to the wild type BMI1, exogenous expression of the mutant BMI1 led to a significant downregulation of p16INK4a and an efficient bypass of cellular senescence in human diploid fibroblasts.

CONCLUSIONS

In summary, our data suggest that the PS domain of BMI1 is involved in its stability and that it negatively regulates function of BMI1 oncoprotein. Our results also suggest that the PS domain of BMI1 could be targeted for the treatment of proliferative disorders such as cancer and aging.

EGFR(S) inhibitors in the treatment of gastro-intestinal cancers: what's new?

In the past 10 to 15 years, a considerable progress has been made in the treatment of gastrointestinal (GI) related malignancies, as number of agents expanded from only one in 1995 to seven in 2006. Current review describes the recent role of targeted therapies, specifically EGFR inhibitors in the treatment of GI cancers. Importance of dietary agents in the treatment and prevention of GI cancers is also reviewed.