Brk is coamplified with ErbB2 to promote proliferation in breast cancer.
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ABSTRACT:
SUBMITTER: Xiang B
PROVIDER: S-EPMC2527934 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Rationale: Dysregulation of the PI3K/AKT/mTOR pathway occurs frequently in cancers, providing an attractive therapeutic target for anticancer treatments. DEPTOR plays essential roles in regulation of cell proliferation and survival by directly modulating mTOR activity. However, whether DEPTOR regulates the growth of ErbB2-positive breast cancer cells remains unknown. Methods: DEPTOR expression was determined by TCGA data analysis and immunohistochemistry of human breast tissue microarrays. The membrane localization of DEPTOR was demonstrated by immunofluorescence and subcellular fractionation. The interaction of DEPTOR with ErbB2 was determined by immunoprecipitation. Furthermore, the biological significance of this interaction was assessed by ATPlite cell growth, clonogenic survival, and flow cytometry-based apoptosis assays. Results: DEPTOR promoted the proliferation and survival of ErbB2-positive breast cancer cells by directly interacting with and stabilizing ErbB2. Specifically, DEPTOR translocates to cell membrane and interacts with ErbB2 to disrupt ErbB2 polyubiquitination and degradation promoted by β-TrCP, an E3 ubiquitin ligase. DEPTOR knockdown destabilizes ErbB2 by shortening its protein half-life to inactivate ErbB2-PI3K-AKT-mTOR signaling, leading to the suppression of cell proliferation and survival by inducing apoptosis. Ectopic expression of a constitutively active ErbB2 mutant completely rescued the reduction in cell proliferation and survival by DEPTOR knockdown. Importantly, DEPTOR expression is increased in human breast cancer tissues and its overexpression correlates with poor patient survival. Moreover, DEPTOR is located on the cell membrane in ErbB2-positive breast cancer tissues, but not in tumor-adjacent normal tissues, indicating that DEPTOR may contribute to the oncogenic characteristics of ErbB2. Conclusions: Our study reveals a novel mechanism by which DEPTOR promotes breast cancer cell proliferation and survival by stabilizing ErbB2.
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Project description:Breast tumor kinase (BRK), also known as protein tyrosine kinase 6 (PTK6), is a non-receptor tyrosine kinase overexpressed in more that 60% of human breast carcinomas. The overexpression of BRK has been shown to sensitize mammary epithelial cells to mitogenic signaling and to promote cell proliferation and tumor formation. The molecular mechanisms of BRK have been unveiled by the identification and characterization of BRK target proteins. Downstream of tyrosine kinases 1 or Dok1 is a scaffolding protein and a substrate of several tyrosine kinases. Herein we show that BRK interacts with and phosphorylates Dok1 specifically on Y362. We demonstrate that this phosphorylation by BRK significantly downregulates Dok1 in a ubiquitin-proteasome-mediated mechanism. Together, these results suggest a novel mechanism of action of BRK in the promotion of tumor formation, which involves the targeting of tumor suppressor Dok1 for degradation through the ubiquitin proteasomal pathway.
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Project description:ERBB2 overexpression in human breast cancer leads to invasive carcinoma but the mechanism is not clearly understood. Here we report that TOM1L1 is co-amplified with ERBB2 and defines a subgroup of HER2(+)/ER(+) tumours with early metastatic relapse. TOM1L1 encodes a GAT domain-containing trafficking protein and is a SRC substrate that negatively regulates tyrosine kinase signalling. We demonstrate that TOM1L1 upregulation enhances the invasiveness of ERBB2-transformed cells. This pro-tumoural function does not involve SRC, but implicates membrane-bound membrane-type 1 MMP (MT1-MMP)-dependent activation of invadopodia, membrane protrusions specialized in extracellular matrix degradation. Mechanistically, ERBB2 elicits the indirect phosphorylation of TOM1L1 on Ser321. The phosphorylation event promotes GAT-dependent association of TOM1L1 with the sorting protein TOLLIP and trafficking of the metalloprotease MT1-MMP from endocytic compartments to invadopodia for tumour cell invasion. Collectively, these results show that TOM1L1 is an important element of an ERBB2-driven proteolytic invasive programme and that TOM1L1 amplification potentially enhances the metastatic progression of ERBB2-positive breast cancers.
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Project description:Basal-type triple-negative breast cancers (TNBC) are aggressive and difficult to treat relative to luminal-type breast cancers. TNBC often express abundant Met receptors and are enriched for transcriptional targets regulated by hypoxia-inducible factor-1α (HIF-1α), which independently predict cancer relapse and increased risk of metastasis. Brk/PTK6 is a critical downstream effector of Met signaling and is required for hepatocyte growth factor (HGF)-induced cell migration. Herein, we examined the regulation of Brk by HIFs in TNBC in vitro and in vivo. Brk mRNA and protein levels are upregulated strongly in vitro by hypoxia, low glucose, and reactive oxygen species. In HIF-silenced cells, Brk expression relied upon both HIF-1α and HIF-2α, which we found to regulate BRK transcription directly. HIF-1α/2α silencing in MDA-MB-231 cells diminished xenograft growth and Brk reexpression reversed this effect. These findings were pursued in vivo by crossing WAP-Brk (FVB) transgenic mice into the MET(Mut) knockin (FVB) model. In this setting, Brk expression augmented MET(Mut)-induced mammary tumor formation and metastasis. Unexpectedly, tumors arising in either MET(Mut) or WAP-Brk × MET(Mut) mice expressed abundant levels of Sik, the mouse homolog of Brk, which conferred increased tumor formation and decreased survival. Taken together, our results identify HIF-1α/2α as novel regulators of Brk expression and suggest that Brk is a key mediator of hypoxia-induced breast cancer progression. Targeting Brk expression or activity may provide an effective means to block the progression of aggressive breast cancers.
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Project description:The Hippo signaling pathway is implicated in regulation of liver size and dysregulation of this pathway contributes to tumorigenesis. The transcriptional targets and downstream pathways of the Hippo pathway effector YAP that contribute to liver growth have yet to be well-characterized. We examined the liver transcriptome in response to YAP overexpression and identify the ErbB signaling pathway as a mediator of cell growth downstream of YAP. ErbB2 is transcriptionally regulated by YAP in both the mouse liver and in HepG2 human hepatoma cells. Knockdown of YAP or pharmacological inhibition with verteporfin reduced ERBB2 levels in HepG2 cells. Analysis of ChIP-seq data revealed enrichment of the transcription factor TEAD4 at the ERBB2 promoter. Using luciferase reporter and chromatin immunoprecipitation assays, we show that YAP and TEAD directly bind to and activate a regulatory element in the ErbB2 promoter in both the mouse liver and HepG2 cells. Functionally, knockdown of YAP reduced EGF-induced ERBB2-mediated HepG2 cell proliferation and PI3K/AKT activation. Our findings highlight a mechanism by which YAP exerts its effects on liver cell proliferation through the ErbB signaling pathway by directly regulating the transcription of ErbB2.
2018-02-09 | GSE110383 | GEO
Project description:Exosomes have recently become the subject of increasing research interest. Interactions between tumor and host cells via exosomes play crucial roles in the initiation, progression and invasiveness of breast cancer. In our study, we used exosomes isolated from a co-culture model of THP-1-derived macrophages exposed to apoptotic MCF-7 or MDA-MB-231 breast cancer cell line cells to investigate their effects on naïve MCF-7 or MDA-MB-231 cells in vitro and in vivo. This post-chemotherapy tumor microenvironment model allowed us to explore possible mechanisms that explain increased proliferation and metastasis of breast cancer seen in some patients. Our results suggest that while exosomes derived from macrophages normally inhibit proliferation and metastasis of MCF-7 or MDA-MB-231 cells, exposure of macrophages to breast cancer cells that have experienced chemotherapy are modified them to promote these processes. Exosomes from macrophages exposed to apoptotic cancer cells have increased amounts of IL-6 that increases the phosphorylation of STAT3, which likely explains the increased transcription of STAT3 target genes such as CyclinD1, MMP2 and MMP9. These observations suggest that the inhibition of exosome secretion and STAT3 signaling pathway activation might suppress the growth and metastasis of malignant tumors, and provide new targets for therapeutic treatment of malignant tumors after chemotherapy.
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Project description:ErbB2, a member of the ErbB family of receptor tyrosine kinases, is an essential player in the cell's growth and proliferation signaling pathways. Amplification or overexpression of ErbB2 is observed in ∼30% of breast cancer patients, and often drives cellular transformation and cancer development. Recently, we have shown that ErbB2 interacts with the nuclear-cytoplasmic shuttling protein nucleolin, an interaction which enhances cell transformation in vitro, and increases mortality risk and disease progression rate in human breast cancer patients. Given these results, and since acquired resistance to anti-ErbB2-targeted therapy is a major obstacle in treatment of breast cancer, we have examined the therapeutic potential of targeting the ErbB2-nucleolin complex. The effect of the nucleolin-specific inhibitor GroA (AS1411) on ErbB2-positive breast cancer was tested in vivo, in a mouse xenograft model for breast cancer; as well as in vitro, alone and in combination with the ErbB2 kinase-inhibitor tyrphostin AG-825. Here, we show that in vivo treatment of ErbB2-positive breast tumor xenografts with GroA reduces tumor size and leads to decreased ErbB2-mediated signaling. Moreover, we found that co-treatment of breast cancer cell lines with GroA and the ErbB2 kinase-inhibitor tyrphostin AG-825 enhances the anti-cancer effects exerted by GroA alone in terms of cell viability, mortality, migration, and invasiveness. We, therefore, suggest a novel therapeutic approach, consisting of combined inhibition of ErbB2 and nucleolin, which has the potential to improve breast cancer treatment efficacy.
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Project description:The PI3K/AKT pathway is the focus of several targeted therapeutic agents for a variety of malignancies. In ERBB2-amplified breast cancer, the hyperactivation of this signaling cascade is associated with resistance to ERBB2-targeted therapy. This can occur through gain-of-function alterations or compensatory mechanisms that enter into play upon pharmacological pressure. The strong rationale in combining anti-ERBB2 agents with PI3K/AKT inhibitors, together with the identification of genomic alterations conferring sensitivity to targeted inhibition, are guiding the design of clinical studies aimed at preventing the emergence of drug resistance and achieving more durable response. In the present review, we describe the involvement of this pathway in breast cancer pathogenesis, with an emphasis on AKT kinases, and provide insight into currently available targeted agents for the treatment of ERBB2-amplified breast cancer. Finally, we provide preliminary data on a novel AKT3 mutation detected in the context of resistance to anti-ERBB2 therapy as an example of genomics-based approaches towards uncovering novel actionable targets in this setting.
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Project description:Triple-negative breast cancer (TNBC) is a highly malignant breast cancer subtype with a poor prognosis. Improved insight into the molecular biology basis of TNBC progression is urgently needed. Herein, we reported that POLD2 was highly expressed in TNBC and patients with high POLD2 expression in their tumors had poor clinical outcomes. In functional studies, knockdown of POLD2 inhibited the proliferation of TNBC. Mechanistically, we revealed that transcription factor E2F1 directly bound to the promoter of POLD2 and regulated its expression in TNBC cells, which in turn contributed to the proliferation of TNBC. Additionally, rescue experiments validated that E2F1-mediated cell proliferation in TNBC was dependent on POLD2. Taken together, our results elucidated a novel mechanism of the E2F1-POLD2 axis in TNBC proliferation, and POLD2 may be a potential therapeutic target for TNBC treatment.
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Project description:Brk, a tyrosine kinase expressed in a majority of breast tumors, but not normal mammary tissue, promotes breast carcinoma cell proliferation. Normal epithelial cells are dependent on cell-cell or cell-matrix interactions for survival and undergo apoptosis after disruption of these interactions. Tumor cells are less sensitive to the induction of apoptosis and are predicted to have the potential to disseminate. We investigated whether Brk has further roles in breast tumor progression by relating its expression to tumor grade and demonstrating its role in the regulation of carcinoma cell survival under non-adherent conditions. Brk expression was determined by reverse transcription PCR on RNA extracted from surgical samples of human breast cancers. Breast carcinoma cell survival in suspension culture was examined when Brk protein levels were suppressed by RNA interference. Additionally, the effect of experimentally overexpressing Brk in otherwise Brk-negative breast carcinoma cells was assessed. Brk mRNA expression was notably higher in grade 3 breast tumors, as compared with lower tumor grades. In suspension culture, Brk suppression increased the rate of cell death, as compared with controls, and this cell death program exhibited characteristics of autophagy but not of apoptosis. Conversely, experimental expression of Brk in Brk-negative cells increased cell survival whereas kinase-inactive Brk did not. Therefore, Brk enhances breast carcinoma cell survival in suspension, suggesting a role for Brk in supporting breast cancer cell dissemination.
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