Next-Generation Therapeutic Targets in Triple-Negative Breast Cancer.

pYtags are novel biosensors that can be used to measure the activity of a receptor tyrosine kinase of interest in live cells with high spatiotemporal resolution and are applied to reveal rapid activity dynamics of EGFR/ErbB2 signaling.

IntroductionDysregulated receptor tyrosine kinase (RTK) signaling is a common occurrence in basal-like and triple-negative breast cancer (BTBC). As a result, RTK-targeting therapies have been initiated but proved difficult, mainly owing to the multiplicity of dysregulated RTKs. Hence, targeting master regulators of RTK signaling might alleviate this obstacle. Before that, however, defining the mechanism of such molecules is required. In this report, we show that the Src homology phosphotyrosyl phosphatase 2 (SHP2) is a master regulator of RTK expression and signaling in BTBC.MethodsXenograft tumor growth studies were used to determine the effect of SHP2 inhibition on tumorigenesis and/or metastasis. Cell proliferation rate, anchorage-independent growth, mammosphere formation, and ALDEFLUOR assays were used to compare the relative functional importance of SHP2 and the epidermal growth factor receptor (EGFR) in BTBC cells. Immunohistochemistry and immunofluorescence analyses were used to determine the state of SHP2 and EGFR coexpression in BTBC. Analysis of mitogenic and cell survival signaling was performed to show SHP2’s role in signaling by multiple RTKs.ResultsInhibition of SHP2 in BTBC cells suppresses their tumorigenic and metastatic properties. Because EGFR is the most commonly dysregulated RTK in BTBC, we first tested the effect of SHP2 inhibition on EGFR signaling and found that SHP2 is important not only for mediation of the Ras/extracellular signal-regulated kinase and the phosphatidyl inositol 3-kinase/Akt signaling pathways but also for the expression of the receptor itself. The existence of a tight association between SHP2 and EGFR expression in tumors and cell lines further suggested the importance of SHP2 in EGFR expression. Comparison of relative biological significance showed the superiority of SHP2 inhibition over that of EGFR, suggesting the existence of additional RTKs regulated by SHP2. Indeed, we found that the expression as well as the signaling efficiency of c-Met and fibroblast growth factor receptor 1, two other RTKs known to be dysregulated in BTBC, are SHP2-dependent. To our knowledge, this is the first demonstration of SHP2 acting both upstream and downstream of RTKs to promote signaling.ConclusionsSHP2 upregulates the expression and signaling of multiple RTKs to promote BTBC. These findings provide a mechanistic explanation for the superiority of SHP2 inhibition in BTBC.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-015-0659-z) contains supplementary material, which is available to authorized users.

The two SH2 (Src homology domain 2) domains present in phospholipase C-gamma1 (PLC-gamma1) were assayed for their capacities to recognize the five autophosphorylation sites in the epidermal growth factor receptor. Plasmon resonance and immunological techniques were employed to measure interactions between SH2 fusion proteins and phosphotyrosine-containing peptides. The N-SH2 domain recognized peptides in the order of pY1173 > pY992 > pY1068 > pY1148 >> pY1086, while the C-SH2 domain recognized peptides in the order of pY992 > pY1068 > pY1148 >> pY1086 and pY1173. The major autophosphorylation site, pY1173, was recognized only by the N-SH2 domain. Contributions of the N-SH2 and C-SH2 domains to the association of the intact PLC-gamma1 molecule with the activated epidermal growth factor (EGF) receptor were assessed in vivo. Loss of function mutants of each SH2 domain were produced in a full-length epitope-tagged PLC-gamma1. After expression of the mutants, cells were treated with EGF and association of exogenous PLC-gamma1 with EGF receptors was measured. In this context the N-SH2 is the primary contributor to PLC-gamma1 association with the EGF receptor. The combined results suggest an association mechanism involving the N-SH2 domain and the pY1173 autophosphorylation site as a primary event and the C-SH2 domain and the pY992 autophosphorylation site as a secondary event.

Epidermal growth factor (EGF) receptor (EGFR) signal transduction is organized by scaffold and adaptor proteins, which have specific subcellular distribution. On a way from the plasma membrane to the lysosome EGFRs are still in their active state and can signal from distinct subcellular locations. To identify organelle-specific targets of EGF receptor signaling on endosomes a combination of subcellular fractionation, two-dimensional DIGE, fluorescence labeling of phosphoproteins, and MALDI-TOF/TOF mass spectrometry was applied. All together 23 EGF-regulated (phospho)proteins were identified as being differentially associated with endosomal fractions by functional organelle proteomics; among them were proteins known to be involved in endosomal trafficking and cytoskeleton rearrangement (Alix, myosin-9, myosin regulatory light chain, Trap1, moesin, cytokeratin 8, septins 2 and 11, and CapZbeta). Interestingly R-Ras, a small GTPase of the Ras family that regulates cell survival and integrin activity, was associated with endosomes in a ligand-dependent manner. EGF-dependent association of R-Ras with late endosomes was confirmed by confocal laser scanning immunofluorescence microscopy and Western blotting of endosomal fractions. EGFR tyrosine kinase inhibitor gefitinib was used to confirm EGF-dependent regulation of all identified proteins. EGF-dependent association of signaling molecules, such as R-Ras, with late endosomes suggests signaling specification through intracellular organelles.

Epidermal Growth Factor Receptor (EGFR) signaling has a conserved role in ethanol-induced behavior in flies and mice, affecting ethanol-induced sedation in both species. However it is not known what other effects EGFR signaling may have on ethanol-induced behavior, or what roles other Receptor Tyrosine Kinase (RTK) pathways may play in ethanol induced behaviors. We examined the effects of both the EGFR and Fibroblast Growth Factor Receptor (FGFR) RTK signaling pathways on ethanol-induced enhancement of locomotion, a behavior distinct from sedation that may be associated with the rewarding effects of ethanol. We find that both EGFR and FGFR genes influence ethanol-induced locomotion, though their effects are opposite – EGFR signaling suppresses this behavior, while FGFR signaling promotes it. EGFR signaling affects development of the Drosophila mushroom bodies in conjunction with the JNK MAP kinase basket (bsk), and with the Ste20 kinase tao, and we hypothesize that the EGFR pathway affects ethanol-induced locomotion through its effects on neuronal development. We find, however, that FGFR signaling most likely affects ethanol-induced behavior through a different mechanism, possibly through acute action in adult neurons.

Disclosure: A. Ocampo: None. P.D. Bagamasbad: None. In breast cancer (BCa), glucocorticoid (GC) therapy is used in anti-emetic and palliative care. However, the effects of GC therapy in BCa are conflicting as it is beneficial for hormone-responsive luminal subtypes while it promotes tumor progression in more aggressive triple-negative BCa (TNBCs). A factor implicated in this paradoxical shift is the feedback inhibitor of epidermal growth factor receptor (EGFR) signaling, ERBB receptor feedback inhibitor 1 (ERRFI1). In BCa cell lines, ERRFI1 expression is directly regulated by GC receptor (GR). More interestingly, ERRFI1 was found to restrict the GC-enhanced proliferation in normal breast epithelia but enhances the GC-mediated pro-tumorigenic effects in highly aggressive TNBC. To identify the mechanism behind the shift in ERFFI1 function through BCa progression, ERRFI1 protein interactions in the luminal, HER2, and TNBC subtypes were analyzed by identifying differentially expressed proteins from each subtype using available proteome and interactome datasets from Integrated Interactions Database and followed by network and clustering analyses through STRING. The ERRFI1 interactome varied across the subtypes, and gene ontology analysis of the protein networks revealed progressive tumorigenic effects from the least aggressive luminal subtype to the most aggressive TNBC. The luminal BCa-ERRFI1 interactome showed metastatic potential that is countered by negative regulation of receptor tyrosine kinase (RTK) signaling. The HER2-ERRFI1 interactome highlighted the amplification of RTK signaling and its possible modulation through SRC while the TNBC-ERRFI1 interactome presents pro-oncogenic proteins implicated in drug resistance, angiogenesis, and EMT. Interestingly, the interactome also revealed a link between EGFR signaling and GR signaling possibly through ERRFI1, EGFR, and SFN. To determine the function of ERFFI1 in EGFR signaling in BCa, we generated stable ERRFI1 knockdown in different breast epithelial cell models through lentiviral transduction. Cells were then treated with EGF followed by gene expression analysis of known EGF-upregulated genes such as MYC, GSK3B, MCL1, and MMP9. We found that ERRFI1 knockdown enhanced the EGF-dependent induction of MYC and MMP9 in normal MCF10A cells and this effect was not observed in the TNBC MDA-MB-468 line, suggesting the loss of ERRFI1-mediated inhibition of EGFR signaling with BCa tumorigenic potential. Taken together, our findings suggest that the progressive loss of anti-tumorigenic function of ERRFI1 may be explained by its changing interactome in BCa molecular subtypes. Presentation: 6/3/2024

Disclosure: A. Ocampo: None. P.D. Bagamasbad: None. In breast cancer (BCa), glucocorticoid (GC) therapy is used in anti-emetic and palliative care. However, the effects of GC therapy in BCa are conflicting as it is beneficial for hormone-responsive luminal subtypes while it promotes tumor progression in more aggressive triple-negative BCa (TNBCs). A factor implicated in this paradoxical shift is the feedback inhibitor of epidermal growth factor receptor (EGFR) signaling, ERBB receptor feedback inhibitor 1 (ERRFI1). In BCa cell lines, ERRFI1 expression is directly regulated by GC receptor (GR). More interestingly, ERRFI1 was found to restrict the GC-enhanced proliferation in normal breast epithelia but enhances the GC-mediated pro-tumorigenic effects in highly aggressive TNBC. To identify the mechanism behind the shift in ERFFI1 function through BCa progression, ERRFI1 protein interactions in the luminal, HER2, and TNBC subtypes were analyzed by identifying differentially expressed proteins from each subtype using available proteome and interactome datasets from Integrated Interactions Database and followed by network and clustering analyses through STRING. The ERRFI1 interactome varied across the subtypes, and gene ontology analysis of the protein networks revealed progressive tumorigenic effects from the least aggressive luminal subtype to the most aggressive TNBC. The luminal BCa-ERRFI1 interactome showed metastatic potential that is countered by negative regulation of receptor tyrosine kinase (RTK) signaling. The HER2-ERRFI1 interactome highlighted the amplification of RTK signaling and its possible modulation through SRC while the TNBC-ERRFI1 interactome presents pro-oncogenic proteins implicated in drug resistance, angiogenesis, and EMT. Interestingly, the interactome also revealed a link between EGFR signaling and GR signaling possibly through ERRFI1, EGFR, and SFN. To determine the function of ERFFI1 in EGFR signaling in BCa, we generated stable ERRFI1 knockdown in different breast epithelial cell models through lentiviral transduction. Cells were then treated with EGF followed by gene expression analysis of known EGF-upregulated genes such as MYC, GSK3B, MCL1, and MMP9. We found that ERRFI1 knockdown enhanced the EGF-dependent induction of MYC and MMP9 in normal MCF10A cells and this effect was not observed in the TNBC MDA-MB-468 line, suggesting the loss of ERRFI1-mediated inhibition of EGFR signaling with BCa tumorigenic potential. Taken together, our findings suggest that the progressive loss of anti-tumorigenic function of ERRFI1 may be explained by its changing interactome in BCa molecular subtypes. Presentation: 6/3/2024

Triple-negative breast cancer (TNBC) accounts for approximately 10-20% of all diagnosed breast cancer. Both epidermal growth factor receptor (EGFR) and vascular endothelial growth factor receptor 2 (VEGFR2) frequently overexpress in TNBC and cooperate with each other in autocrine and paracrine manner to enhance tumor growth and angiogenesis. Therapeutic mAbs targeting EGFR (cetuximab) and VEGFR2 (ramucirumab) are approved by FDA for numerous cancer indications, but none of them are approved to treat breast cancers. TNBC cells secrete VEGF-A, which mediate angiogenesis on endothelial cells in a paracrine fashion and promote cancer cell growth in autocrine manner. To disrupt autocrine/paracrine loop in TNBC models in addition to mediating anti-EGFR tumor growth signaling and anti-VEGFR2 angiogenic pathway, we generated a bispecific antibody co-targeting EGFR and VEGFR2 (designated as anti-EGFR/VEGFR2 BsAb), in which cetuximab IgG backbone is connected to the single chain variable fragment (scFv) of ramucirumab via a glycine linker. Physiochemical characterization data shows that anti-EGFR/VEGFR2 BsAb binds to both EGFR and VEGFR2 in a similar binding affinity comparable to parental antibodies. Anti-EGFR/VEGFR2 BsAb demonstrates potent in vitro and in vivo anti-tumor activity in TNBC models. Mechanistically, anti-EGFR/VEGFR2 BsAb not only directly inhibits both EGFR and VEGFR2 in TNBC cells but also disrupts autocrine mechanism in TNBC xenograft mouse model. Furthermore, anti-EGFR/VEGFR2 BsAb blocks paracrine pathway mediated by VEGF/VEGFR2 in endothelial cells. Collectively, our novel findings demonstrate that anti-EGFR/VEGFR2 BsAb inhibits tumor growth via multiple mechanisms of action and has potential to be developed as an attractive targeted therapy for TNBC. Citation Format: Nishant Mohan, Xiao Luo, Yi Shen, Zachary Olson, Atul Agrawal, Yukinori Endo, David Rotstein, Lorraine Pelosof, Wen Jin Wu. Physiochemical and biological characterization of anti-EGFR based bispecific antibodies in triple negative breast cancer (TNBC) models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5310.

Epidermal growth factor receptor (EGFR) signaling inhibition by monoclonal antibodies and EGFR-specific tyrosine kinase inhibitors has shown clinical efficacy in cancer by restoring susceptibility of tumor cells to therapeutic apoptosis induction. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promising anti-cancer agent with tumor-selective apoptotic activity. Here we present a novel approach that combines EGFR-signaling inhibition with target cell-restricted apoptosis induction using a TRAIL fusion protein with engineered specificity for EGFR. This fusion protein, scFv425:sTRAIL, comprises the EGFR-blocking antibody fragment scFv425 genetically fused to soluble TRAIL (sTRAIL). Treatment with scFv425:sTRAIL resulted in the specific accretion to the cell surface of EGFR-positive cells only. EGFR-specific binding rapidly induced a dephosphorylation of EGFR and down-stream mitogenic signaling, which was accompanied by cFLIP(L) down-regulation and Bad dephosphorylation. EGFR-specific binding converted soluble scFv425:sTRAIL into a membrane-bound form of TRAIL that cross-linked agonistic TRAIL receptors in a paracrine manner, resulting in potent apoptosis induction in a series of EGFR-positive tumor cell lines. Co-treatment of EGFR-positive tumor cells with the EGFR-tyrosine kinase inhibitor Iressa resulted in a potent synergistic pro-apoptotic effect, caused by the specific down-regulation of c-FLIP. Furthermore, in mixed culture experiments binding (L)of scFv425:sTRAIL to EGFR-positive target cells conveyed a potent apoptotic effect toward EGFR-negative bystander tumor cells. The favorable characteristics of scFv425:sTRAIL, alone and in combination with Iressa, as well as its potent anti-tumor bystander activity indicate its potential value for treatment of EGFR-expressing cancers.

Background: Triple-negative breast cancer (TNBC) is lack of effective targeted therapies. Epidermal growth factor receptor (EGFR) is a potential therapeutic target for TNBC. However, TNBC is resistant to EGFR-targeted drugs in clinical trials, and the tolerance mechanism remains unclear. This study aimed to elucidate the possible resistance mechanism for TNBC to EGFR-targeted therapy and how sensitize TNBC cells to erlotinib. Methods: PDZ domain containing 1 (PDZK1) correlated with TNBC development was screened out by bioinformatics analysis and its correlation with resistance to erlotinib was identified by western blotting (WB). Its interaction with EGFR and structural basis were determined by GST-Pull down and coimmunoprecipitation. Its regulation on EGFR signaling activation and expression level were detected by WB in PDZK1 overexpression and knockdown TNBC cells, xenograft tissues and correlation analyses. Correlation was performed by gene set enrichment analysis (GSEA) and immunohistochemistry of tissue microarray followed by Pearson analysis. TNBC-suppressing effects of PDZK1 and its sensitizing effects on erlotinib were investigated using cell viability assay, colony-forming assay, wound healing assay, Matrigel invasion assay and xenograft model in combination with PDZK1 wild type/mutant transfection and rescue experiment. Results: Here we found that PDZK1 was correlated with TNBC development and its level was downregulated in erlotinib-resistant TNBC cells, suggesting that PDZK1 downregulation was related to erlotinib resistance in TNBC. PDZK1 bound with EGFR. Through the interaction, PDZK1 promoted EGFR degradation by enhancing the binding of EGFR with c-Cbl and inhibited EGFR phosphorylation by hindering EGFR dimerization. PDZK1 was specifically downregulated in TNBC tissues and was correlated with poor prognosis of TNBC. Functional assays in vitro and in vivo showed that PDZK1 suppressed TNBC development. Restoring EGFR expression and kinase inhibitor treatment reversed the malignancy caused by PDZK1 overexpression and knockdown, respectively. PDZK1 wild type, but not mutant overexpression enhanced the inhibitory effect of erlotinib on EGFR signaling and TNBC malignancy in vitro and in vivo. Conclusion: PDZK1 is a significant prognostic factor for TNBC and a potential molecular therapeutic target for TNBC to reverse the tolerance of TNBC cells to erlotinib. Citation Format: Junfang Zheng, Yuanzhen Ma, Zhiyu Fang, Yijun Qi. PDZK1 sensitizes TNBC cells to erlotinib via promoting c-Cbl-mediated EGFR degradation and inhibiting EGFR phosphorylation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 549.

The murine retroviral oncogene v-cbl induces pre-B cell lymphomas and myelogenous leukemias. The protein product of the mammalian c-cbl proto-oncogene is a widely expressed cytoplasmic 120-kDa protein (p120cbl) whose normal cellular function has not been determined. Here we show that upon stimulation of human epidermal growth factor (EGF) receptor, p12ocbl becomes strongly tyrosine-phosphorylated and associates with activated EGF receptor in vivo. A GST fusion protein containing amino acids 1-486 of p120cbl, including a region highly conserved in nematodes, binds directly to the autophosphorylated carboxyl-terminal tail of the EGF receptor. Platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), or nerve growth factor (NGF) stimulation also results in tyrosine phosphorylation of p120cbl. Recent genetic studies in Caenorhabditis elegans indicate that Sli-1, a p120cbl homologue, plays a negative regulatory role in control of the Ras signaling pathway initiated by the C. elegans EGF receptor homologue. Our results indicate that p120cbl is involved in an early step in the EGF signaling pathway that is conserved from nematodes to mammals.

Epidermal growth factor receptor as a potential therapeutic target in triple-negative breast cancer

Immunotherapy has transformed cancer treatment, yet durable responses to immune checkpoint blockade (ICB) are limited to a subset of patients. Identifying tumor-intrinsic resistance mechanisms is critical to improving ICB efficacy and outcomes. We recently identified crosstalk between lipid metabolism via the downregulation of ceramide synthase 4 (CerS4) and internalized programmed death-ligand 1 (PD-L1) signaling, which promotes metastasis and impairs ICB response. Our data also demonstrated that αPD-L1 therapy enhanced internalized PD-L1 signaling, suggesting a role in adaptive ICB resistance. To investigate the underlying mechanism, we established an E0771-allograft-based triple-negative breast cancer (TNBC) model of ICB resistance, E0771-2RA, through serial αPD-L1 treatment and subculturing of resistant tumors. The 2RA model is resistant to both αPD-L1 and αPD-1 therapy in-vivo, with reduced CerS4/ceramide levels and increased PD-L1 internalization, consistent with our prior findings. Whole transcriptomic RNA sequencing of E0771 and 2RA tumors revealed enrichment in epidermal growth factor receptor (EGFR) and prostaglandin E2 (PGE2) signaling in 2RA tumors. Mechanistically, we found that (1) EGFR signaling negatively regulates CerS4 expression; (2) CerS4 suppression enhances PD-L1 internalization and subsequent association with Caprin-1; and (3) the intracellular PD-L1-Caprin-1 complex stabilizes prostaglandin-endoperoxide synthase 2 (Ptgs2, Cox2) mRNA to promote PGE2 production. Immune profiling of E0771 and 2RA tumors using flow cytometry and single-nuclei RNA sequencing revealed M2 macrophage polarization, PMN-MDSC recruitment, and T cell dysfunction in 2RA tumors. However, pharmacological targeting of PGE2 signaling and exogenous CerS4/ceramide restoration in ICB-resistant 2RA tumors primarily alleviated T cell dysfunction, suggesting the T cell compartment is the primary target of this signaling axis. Single-nuclei RNA sequencing and CellChat analyses revealed abundant TGF-β signaling in 2RA tumors, which we found to regulate PD-L1 internalization in-vitro, presenting a possible therapeutic vulnerability. Thus, to target this mechanism, we combined αPD-1 therapy with TGF-β inhibition in-vivo, which restored ICB sensitivity and prolonged survival. Using TCGA and human ICB resistance datasets, we validated the link between EGFR, CerS4, PD-L1, and PGE2 signaling in TNBC, head and neck squamous cell carcinoma (HNSCC), and melanoma. Based on our mechanistic and sequencing data, we additionally curated a gene signature to predict ICB response vs. resistance in solid tumors. Our findings uncover a novel mechanistic link between altered CerS4-dependent lipid metabolism, EGFR, PD-L1, and PGE2 signaling and introduce mechanism-based therapeutic strategies for overcoming ICB resistance in solid tumors. Citation Format: Wyatt O. Wofford, Han Gyul Lee, Bryan Granger, Elif Percin, Mohamed Faisal Kassir, Lucy Mulligan, Odai Darawshi, Paramita Chakarborty, Salih Gencer, Natalia Oleinik, Stefano Berto, Shikhar Mehrotra, Besim Ogretmen. Altered lipid metabolism drives immunotherapy resistance via an EGFR/CERS4/PD-L1/PGE2 signaling axis in solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 929.

Background: Triple-negative breast cancers (TNBC) lack targeted therapeutic strategies and identification of potential oncogenic targets is imperative. Fibroblast growth factor (FGF) pathway has been implicated in mammary tumorigenesis and is a potential target in TNBC. Amplification of FGFR2 (fibroblast growth factor receptor 2), identified using genomic studies, has been reported in 4% of TNBCs. Selective FGFR inhibitors are in clinical development and patient selection for these trials is important. Preclinical data suggests that cell lines with FGFR amplification are sensitive to FGFR inhibitors. The aim of this study was to identify FGFR1 and FGFR2 amplification in TNBCs using a quantitative and sensitive methodology of digital droplet polymerase chain reaction (ddPCR) and compare to our results from a DNA-based microarray analysis. Methods: Fresh-frozen breast tumor core biopsies were collected from patients enrolled onto a TNBC neoadjuvant clinical trial. DNA from each tumor and matched germline-derived sample (n=56 pairs) was hybridized to Affymetrix Molecular Inversion Probe (MIP) array to determine copy number variation (CNV). ddPCR was used to assess amplification in FGFR1 and FGFR2 in 11 and 53 tumor/ germline DNA sample pairs respectively. The ddPCR technology utilizes TaqMan chemistry PCR primers and probes specific for FGFR1 and FGFR2. It quantitates copy number by streaming emulsion droplets single-file into a capillary that leads past a two-color detector, where the positive droplets for the target and reference genes are quantified. Copy numbers for target genes are calculated by comparing to an internal control (ultra-conserved region of chromosome 1). Results: CNV in FGFR1 and FGFR2 was assessed in 56 TNBCs. No FGFR1 amplifications were identified in any of the samples. FGFR2 amplifications were identified in 2/56 (4%) tumor samples. ddPCR was used to assess quantitative copy number in 53 paired tumor/ germline DNA samples for FGFR2 and 11 paired samples for FGFR1. High amplifications with 6-8 copies of FGFR2 were identified in 2/53 (4%) of the TNBCs. These two samples were the same as the ones identified to have a high copy gain by CNV analysis. No FGFR1 amplifications were identified by ddPCR and this was consistent with our CNV analysis result. Conclusions: Our FGFR amplification results were in congruence using two different methodologies. No FGFR1 amplification was identified in the TNBC samples assessed and FGFR2 amplification was identified in 4%. ddPCR was done on fresh-frozen TNBCs in this study but this technology can be applied to formalin fixed paraffin embedded tumors as well. ddPCR can detect multiple cancer genome amplifications and has a potential for large scale application. There are several FGFR inhibitors in clinical trials and ddPCR methodology is a clinically applicable strategy for identifying patients with FGFR amplification. Citation Format: Shaveta Vinayak, Lincoln D. Nadauld, Laura Miotke, Rowza T. Rumma, Melinda L. Telli, Hanlee P. Ji, James M. Ford. Detection of FGFR1 and FGFR2 amplification in triple-negative breast cancer using digital droplet PCR and DNA-based microarrays. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4130. doi:10.1158/1538-7445.AM2013-4130

Activated epidermal growth factor receptor (EGFR) continues to signal in the early endosome, but how this signaling process is regulated is less well understood. Here we describe a protein complex consisting of TIP30, endophilin B1, and acyl-CoA synthetase long chain family member 4 (ACSL4) that interacts with Rab5a and regulates EGFR endocytosis and signaling. These proteins are required for the proper endocytic trafficking of EGF-EGFR. Knockdown of TIP30, ACSL4, endophilin B1, or Rab5a in human liver cancer cells or genetic knock-out of Tip30 in mouse primary hepatocytes results in the trapping of EGF-EGFR complexes in early endosomes, leading to delayed EGFR degradation and prolonged EGFR signaling. Furthermore, we show that Rab5a colocalizes with vacuolar (H(+))-ATPases (V-ATPases) on transport vesicles. The TIP30 complex facilitates trafficking of Rab5a and V-ATPases to EEA1-positive endosomes in response to EGF. Together, these results suggest that this TIP30 complex regulates EGFR endocytosis by facilitating the transport of V-ATPases from trans-Golgi network to early endosomes.