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.

SUMMARY 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.

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 qPCR and in situ hybridization. Alterations in gene expression by TGFβ1 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, VCAN) that is associated with poor overall survival 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 TGFβ1 signaling and is enriched in metastases in comparison to 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 and invasion and tumor progression in mice. Conclusion Our findings suggest that collagen-remodeling genes regulated by TGFβ1 signaling promote metastasis and contribute to poor overall survival in patients with serous ovarian cancer. Our 10-gene signature has both predictive value and biological relevance and thus may be useful as a therapeutic target.

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. Cancer Res; 70(10); 3870-6. ©2010 AACR.

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Breast cancer is the most common cancer in women and a leading cause of cancer-related deaths for women worldwide. Various cell models have been developed to study breast cancer tumorigenesis, metastasis, and drug sensitivity. The MCF10A human mammary epithelial cell line is a widely used in vitro model for studying normal breast cell function and transformation. However, there is limited knowledge about whether MCF10A cells reliably represent normal human mammary cells. MCF10A cells were grown in monolayer, suspension (mammosphere culture), three-dimensional (3D) “on-top” Matrigel, 3D “cell-embedded” Matrigel, or mixed Matrigel/collagen I gel. Suspension culture was performed with the MammoCult medium and low-attachment culture plates. Cells grown in 3D culture were fixed and subjected to either immunofluorescence staining or embedding and sectioning followed by immunohistochemistry and immunofluorescence staining. Cells or slides were stained for protein markers commonly used to identify mammary progenitor and epithelial cells. MCF10A cells expressed markers representing luminal, basal, and progenitor phenotypes in two-dimensional (2D) culture. When grown in suspension culture, MCF10A cells showed low mammosphere-forming ability. Cells in mammospheres and 3D culture expressed both luminal and basal markers. Surprisingly, the acinar structure formed by MCF10A cells in 3D culture was positive for both basal markers and the milk proteins β-casein and α-lactalbumin. MCF10A cells exhibit a unique differentiated phenotype in 3D culture which may not exist or be rare in normal human breast tissue. Our results raise a question as to whether the commonly used MCF10A cell line is a suitable model for human mammary cell studies.

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 ␤-catenin signaling pathway. Consistent with this, IRSs were found to bind ␤-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.Insulin receptor substrates (IRSs) are a family of intracellular proteins that integrate and coordinate hormone, cytokine, and growth factor signaling. To date, four IRS proteins (IRS-1 to IRS-4) have been identified (27). All IRSs contain multiple tyrosine phosphorylation sites that act as binding sites for SH2-containing proteins (27). The IRS proteins were first identified as substrates and presumed signaling intermediates of the insulin receptor. However, it is now clear that the IRS proteins can be activated and phosphorylated by a number of other signaling pathways, including those that are critical for mammary gland development, such as growth hormone and prolactin (2, 56).Much research has focused on the roles of IRSs in both metabolic and mitogenic signaling; however, the last several years have seen an emergence of literature implicating IRSs in human cancer. IRS-1 is constitutively active and phosphorylated in many tumors (6). IRS-1 levels are increased in patients with pancreatic cancer (1), and both IRS-1 and IRS-2 levels are increased in patients with hepatocellular cancer (3, 36). We previously reported that high IRS-1 levels are associated with poor outcomes for patients with breast cancer (25, 41), and this is supported by further studies showing that IRS-1 is expressed in patients with primary breast cancer and metastases, and its levels correlate with poor differentiation and lymph node involvement (22). One study, however, found that IRS-1 levels in advanced primary breast cancers were reduced compared to breasts from healthy patients (44).The mouse mammary gland has served as a useful area for the identification and characterization of oncogenes and tumor suppressor genes important in human breast cancer (15). For example, transgenic mice overexpressing the HER-2 oncogene develop mammary cancer with biological and phenotypic variances similar to those observed in human breast cancer patients (23).To date, there have been no re...

Although interactions between estrogen and growth factor signaling pathways have been studied extensively, how growth factors and progesterone regulate each other is less clear. In this study, we found that IGF-I sharply lowers progesterone receptor (PR) mRNA and protein levels in breast cancer cells. Other growth factors, such as epidermal growth factor, also showed the same effect. The decrease of PR levels was associated with reduced PR activity. Unlike progestins, IGF-I does not utilize the proteasome for down-regulating PR. Instead, the IGF-I-mediated decrease in PR levels is via an inhibition of PR gene transcription. In addition, the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway was found to be specifically involved in this IGF-I effect. Our data also suggest that the IGF-I down-regulation of PR is not mediated via a reduction of estrogen receptor (ER) levels or activity. First, IGF-I induced ligand-independent ER activity while reducing ER-dependent PR levels. Second, whereas PR and cyclin D1 are both ER up-regulated, IGF-I increased cyclin D1 levels while decreasing PR levels. Third, constitutively active PI3K or Akt induced ER activity but reduced PR levels and activity. Taken together, our data indicate that IGF-I inhibits PR expression in breast cancer cells via the PI3K/Akt/mTOR pathway. Because low or absent PR in primary breast cancer is associated with poor prognosis and response to hormone therapy, our results suggest that low PR status may serve as an indicator of activated growth factor signaling in breast tumor cells, and therefore of an aggressive tumor phenotype and resistance against hormonal therapy.