Xiaojiang Cui

Biology of Progesterone Receptor Loss in Breast Cancer and Its Implications for Endocrine Therapy

The response to endocrine therapy in breast cancer correlates with estrogen receptor (ER) and progesterone receptor (PR) status. ER-positive/PR-negative breast cancers respond less well to selective ER modulator (SERM) therapy than ER-positive/PR-positive tumors. The predictive value of PR has long been attributed to the dependence of PR expression on ER activity, with the absence of PR reflecting a nonfunctional ER and resistance to hormonal therapy. However, recent clinical and laboratory evidence suggests that ER-positive/PR-negative breast cancers may be specifically resistant to SERMs, whereas they may be less resistant to estrogen withdrawal therapy with aromatase inhibitors, which is a result inconsistent with the nonfunctional ER theory. Novel alternative molecular mechanisms potentially explaining SERM resistance in ER-positive/PR-negative tumors have been suggested by recent experimental indications that growth factors may downregulate PR levels. Thus, the absence of PR may not simply indicate a lack of ER activity, but rather may reflect hyperactive cross talk between ER and growth factor signaling pathways that downregulate PR even as they activate other ER functions. Therefore, ER-positive/PR-negative breast tumors might best be treated by completely blocking ER action via estrogen withdrawal with aromatase inhibitors, by targeted ER degradation, or by combined therapy targeting both ER and growth factor signaling pathways. In this review, we will discuss the biology and etiology of ER-positive/PR-negative breast cancer, highlighting recent data on molecular cross talk between ER and growth factor signaling pathways and demonstrating how PR might be a useful marker of these activities. Finally, we will consider the clinical implications of these observations.

Expression of Autotaxin and Lysophosphatidic Acid Receptors Increases Mammary Tumorigenesis, Invasion, and Metastases

Lysophosphatidic acid (LPA) acts through high-affinity G protein-coupled receptors to mediate a plethora of physiological and pathological activities associated with tumorigenesis. LPA receptors and autotaxin (ATX/LysoPLD), the primary enzyme producing LPA, are aberrantly expressed in multiple cancer lineages. However, the role of ATX and LPA receptors in the initiation and progression of breast cancer has not been evaluated. We demonstrate that expression of ATX or each edg family LPA receptor in mammary epithelium of transgenic mice is sufficient to induce a high frequency of late-onset, estrogen receptor (ER)-positive, invasive, and metastatic mammary cancer. Thus, ATX and LPA receptors can contribute to the initiation and progression of breast cancer.

FOXC1 Is a Potential Prognostic Biomarker with Functional Significance in Basal-like Breast Cancer

Gene expression signatures for a basal-like breast cancer (BLBC) subtype have been associated with poor clinical outcomes, but a molecular basis for this disease remains unclear. Here, we report overexpression of the transcription factor FOXC1 as a consistent feature of BLBC compared with other molecular subtypes of breast cancer. Elevated FOXC1 expression predicted poor overall survival in BLBC (P = 0.0001), independently of other clinicopathologic prognostic factors including lymph node status, along with a higher incidence of brain metastasis (P = 0.02) and a shorter brain metastasis-free survival in lymph node-negative patients (P < 0.0001). Ectopic overexpression of FOXC1 in breast cancer cells increased cell proliferation, migration, and invasion, whereas shRNA-mediated FOXC1 knockdown yielded opposite effects. Our findings identify FOXC1 as a theranostic biomarker that is specific for BLBC, offering not only a potential prognostic candidate but also a potential molecular therapeutic target in this breast cancer subtype.

Mammary Tumorigenesis and Metastasis Caused by Overexpression of Insulin Receptor Substrate 1 (IRS-1) or IRS-2

ABSTRACT Insulin receptor substrates (IRSs) are signaling adaptors that play a major role in the metabolic and mitogenic actions of insulin and insulin-like growth factors. Reports have recently noted increased levels, or activity, of IRSs in many human cancers, and some have linked this to poor patient prognosis. We found that overexpressed IRS-1 was constitutively phosphorylated in vitro and in vivo and that transgenic mice overexpressing IRS-1 or IRS-2 in the mammary gland showed progressive mammary hyperplasia, tumorigenesis, and metastasis. Tumors showed extensive squamous differentiation, a phenotype commonly seen with activation of the canonical β-catenin signaling pathway. Consistent with this, IRSs were found to bind β-catenin in vitro and in vivo. IRS-induced tumorigenesis is unique, given that the IRSs are signaling adaptors with no intrinsic kinase activity, and this supports a growing literature indicating a role for IRSs in cancer. This study defines IRSs as oncogene proteins in vivo and provides new models to develop inhibitors against IRSs for anticancer therapy.

Oncogenic transformation by the signaling adaptor proteins insulin receptor substrate (IRS)-1 and IRS-2.

Insulin receptor substrates (IRSs) are adaptor proteins that link signaling from upstream activators to multiple downstream effectors to modulate normal growth, metabolism, survival, and differentiation. Recent cell culture studies have shown that IRSs can interact with, and are functionally required for, the transforming ability of many oncogenes. Consistent with this, IRSs are elevated and hyperactive in many human tumors. IRSs respond to many extracellular signals that are critical for mammary gland development, and we have shown that IRSs disrupt normal mammary acini formation in vitro, and cause mammary tumorigenesis and metastasis in vivo. In this review we will discuss the role of IRSs in both transformation and cancer progression.

A Collagen-Remodeling Gene Signature Regulated by TGF-β Signaling Is Associated with Metastasis and Poor Survival in Serous Ovarian Cancer

Purpose: To elucidate molecular pathways contributing to metastatic cancer progression and poor clinical outcome in serous ovarian cancer. Experimental Design: Poor survival signatures from three different serous ovarian cancer datasets were compared and a common set of genes was identified. The predictive value of this gene signature was validated in independent datasets. The expression of the signature genes was evaluated in primary, metastatic, and/or recurrent cancers using quantitative PCR and in situ hybridization. Alterations in gene expression by TGF-β1 and functional consequences of loss of COL11A1 were evaluated using pharmacologic and knockdown approaches, respectively. Results: We identified and validated a 10-gene signature (AEBP1, COL11A1, COL5A1, COL6A2, LOX, POSTN, SNAI2, THBS2, TIMP3, and VCAN) that is associated with poor overall survival (OS) in patients with high-grade serous ovarian cancer. The signature genes encode extracellular matrix proteins involved in collagen remodeling. Expression of the signature genes is regulated by TGF-β1 signaling and is enriched in metastases in comparison with primary ovarian tumors. We demonstrate that levels of COL11A1, one of the signature genes, continuously increase during ovarian cancer disease progression, with the highest expression in recurrent metastases. Knockdown of COL11A1 decreases in vitro cell migration, invasion, and tumor progression in mice. Conclusion: Our findings suggest that collagen-remodeling genes regulated by TGF-β1 signaling promote metastasis and contribute to poor OS in patients with serous ovarian cancer. Our 10-gene signature has both predictive value and biologic relevance and thus may be useful as a therapeutic target. Clin Cancer Res; 20(3); 711–23. ©2013 AACR.

Thioredoxin-like 2 regulates human cancer cell growth and metastasis via redox homeostasis and NF-κB signaling

Cancer cells have an efficient antioxidant system to counteract their increased generation of ROS. However, whether this ability to survive high levels of ROS has an important role in the growth and metastasis of tumors is not well understood. Here, we demonstrate that the redox protein thioredoxin-like 2 (TXNL2) regulates the growth and metastasis of human breast cancer cells through a redox signaling mechanism. TXNL2 was found to be overexpressed in human cancers, including breast cancers. Knockdown of TXNL2 in human breast cancer cell lines increased ROS levels and reduced NF-κB activity, resulting in inhibition of in vitro proliferation, survival, and invasion. In addition, TXNL2 knockdown inhibited tumorigenesis and metastasis of these cells upon transplantation into immunodeficient mice. Furthermore, analysis of primary breast cancer samples demonstrated that enhanced TXNL2 expression correlated with metastasis to the lung and brain and with decreased overall patient survival. Our studies provided insight into redox-based mechanisms underlying tumor growth and metastasis and suggest that TXNL2 could be a target for treatment of breast cancer.

The IGF Pathway Regulates ERα through a S6K1-Dependent Mechanism in Breast Cancer Cells

The IGF pathway stimulates malignant behavior of breast cancer cells. Herein we identify the mammalian target of rapamycin (mTOR)/S6 kinase 1 (S6K1) axis as a critical component of IGF and estrogen receptor (ER)α cross talk. The insulin receptor substrate (IRS) adaptor molecules function downstream of IGF-I receptor and dictate a specific biological response, in which IRS-1 drives proliferation and IRS-2 is linked to motility. Although rapamycin-induced mTOR inhibition has been shown to block IGF-induced IRS degradation, we reveal differential effects on motility (up-regulation) and proliferation (down-regulation). Because a positive correlation between IRS-1 and ERα expression is thought to play a central role in the IGF growth response, we investigated the potential role of ERα as a downstream mTOR target. Small molecule inhibition and targeted knockdown of S6K1 blocked the IGF-induced ERα(S167) phosphorylation and did not influence ligand-dependent ERα(S118) phosphorylation. Inhibition of S6K1 kinase activity consequently ablated IGF-stimulated S6K1/ERα association, estrogen response element promoter binding and ERα target gene transcription. Moreover, site-specific ERα(S167) mutation reduced ERα target gene transcription and blocked IGF-induced colony formation. These findings support a novel link between the IGF pathway and ERα, in which the translation factor S6K1 affects transcription of ERα-regulated genes.

Sustained c-Jun-NH2-Kinase Activity Promotes Epithelial-Mesenchymal Transition, Invasion, and Survival of Breast Cancer Cells by Regulating Extracellular Signal-Regulated Kinase Activation

The c-Jun NH2-terminus kinase (JNK) mediates stress-induced apoptosis and the cytotoxic effect of anticancer therapies. Paradoxically, recent clinical studies indicate that elevated JNK activity in human breast cancer is associated with poor prognosis. Here, we show that overexpression of a constitutively active JNK in human breast cancer cells did not cause apoptosis, but actually induced cell migration and invasion, a morphologic change associated with epithelial-mesenchymal transition (EMT), expression of mesenchymal-specific markers vimentin and fibronectin, and activity of activator protein transcription factors. Supporting this observation, mouse mammary tumor cells that have undergone EMT showed upregulated JNK activity, and the EMT was reversed by JNK inhibition. Sustained JNK activity enhanced insulin receptor substrate-2–mediated ERK activation, which in turn increased c-Fos expression and activator protein activity. In addition, hyperactive JNK attenuated the apoptosis of breast cancer cells treated by the chemotherapy drug paclitaxel, which is in contrast to the requirement for inducible JNK activity in response to cytotoxic chemotherapy. Blockade of extracellular signal-regulated kinase activity diminished hyperactive JNK-induced cell invasion and survival. Our data suggest that the role of JNK changes when its activity is elevated persistently above the basal levels associated with cell apoptosis, and that JNK activation may serve as a marker of breast cancer progression and resistance to cytotoxic drugs. Mol Cancer Res; 8(2); 266–77

FOXC1 regulates the functions of human basal-like breast cancer cells by activating NF-κB signaling

Human basal-like breast cancer (BLBC) is an enigmatic and aggressive malignancy with a poor prognosis. There is an urgent need to identify therapeutic targets for BLBC, because current treatment modalities are limited and not effective. The forkhead box transcription factor FOXC1 has recently been identified as a critical functional biomarker for BLBC. However, how it orchestrates BLBC cells was not clear. Here we show that FOXC1 activates the transcription factor nuclear factor-κB (NF-κB) in BLBC cells by increasing p65/RelA protein stability. High NF-κB activity has been associated with estrogen receptor-negative breast cancer, particularly BLBC. The effect of FOXC1 on p65/RelA protein stability is mediated by increased expression of Pin1, a peptidyl-prolyl isomerase. FOXC1 requires NF-κB for its regulation of cell proliferation, migration and invasion. Notably, FOXC1 overexpression renders breast cancer cells more susceptible to pharmacological inhibition of NF-κB. These results suggest that BLBC cells may rely on FOXC1-driven NF-κB signaling. Interventions of this pathway may provide modalities for the treatment of BLBC.