Angelo J. Casa

Insulin-Like Growth Factor-I Activates Gene Transcription Programs Strongly Associated With Poor Breast Cancer Prognosis

PURPOSE Substantial evidence implicates insulin-like growth factor-I (IGF-I) signaling in the development and progression of breast cancer. To more clearly elucidate the role of IGF in human breast cancer, we identified and then examined gene expression patterns of IGF-I-treated breast cancer cells. METHODS MCF-7 cells were stimulated with IGF-I for 3 or 24 hours and were profiled for greater than 22,000 RNA transcripts. We defined an IGF-I signature pattern of more than 800 genes that were up- or downregulated at both time points. The gene signature was examined in clinical breast tumors and in experimental models that represented other oncogenic pathways. The signature was correlated with clinical and pathologic variables and with patient outcome. RESULTS IGF-I caused temporal changes in gene expression that were strongly associated with cell proliferation, metabolism, and DNA repair. Genes with early and sustained regulation by IGF-I were highly enriched for transcriptional targets of the estrogen receptor (ER), Ras/extracellular signal-related kinase 1/2, and phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin pathways. In three large, independent data sets of profiled human breast tumors, the IGF-I signature was manifested in the majority of ER-negative breast tumors and in a subset (approximately 25%) of ER-positive breast tumors. Patients who had tumors that manifested the IGF-I signature (including patients who did not receive adjuvant therapy) had a shorter time to a poor outcome event. The IGF gene signature was highly correlated with numerous poor prognostic factors and was one of the strongest indicators of disease outcome. CONCLUSION Transcriptional targets of IGF-I represent pathways of increased aggressiveness and possibly hormone independence in clinical breast cancers.

Proteomic and transcriptomic profiling reveals a link between the PI3K pathway and lower estrogen-receptor (ER) levels and activity in ER+ breast cancer.

IntroductionAccumulating evidence suggests that both levels and activity of the estrogen receptor (ER) and the progesterone receptor (PR) are dramatically influenced by growth-factor receptor (GFR) signaling pathways, and that this crosstalk is a major determinant of both breast cancer progression and response to therapy. The phosphatidylinositol 3-kinase (PI3K) pathway, a key mediator of GFR signaling, is one of the most altered pathways in breast cancer. We thus examined whether deregulated PI3K signaling in luminal ER+ breast tumors is associated with ER level and activity and intrinsic molecular subtype.MethodsWe defined two independent molecular signatures of the PI3K pathway: a proteomic (reverse-phase proteomic array) PI3K signature, based on protein measurement for PI3K signaling intermediates, and a PI3K transcriptional (mRNA) signature based on the set of genes either induced or repressed by PI3K inhibitors. By using these signatures, we scored each ER+ breast tumor represented in multiple independent expression-profiling datasets (four mRNA, n = 915; one protein, n = 429) for activation of the PI3K pathway. Effects of PI3K inhibitor BEZ-235 on ER expression and activity levels and cell growth were tested by quantitative real-time PCR and cell proliferation assays.ResultsWithin ER+ tumors, ER levels were negatively correlated with the PI3K activation scores, both at the proteomic and transcriptional levels, in all datasets examined. PI3K signature scores were also higher in ER+ tumors and cell lines of the more aggressive luminal B molecular subtype versus those of the less aggressive luminal A subtype. Notably, BEZ-235 treatment in four different ER+ cell lines increased expression of ER and ER target genes including PR, and treatment with IGF-I (which signals via PI3K) decreased expression of ER and target genes, thus further establishing an inverse functional relation between ER and PI3K. BEZ-235 had an additional effect on tamoxifen in inhibiting the growth of a number of ER+ cell lines.ConclusionsOur data suggest that luminal B tumors have hyperactive GFR/PI3K signaling associated with lower ER levels, which has been correlated with resistance to endocrine therapy. Targeting PI3K in these tumors might reverse loss of ER expression and signaling and restore hormonal sensitivity.

Proteasome inhibition represses ERα gene expression in ER+ cells: a new link between proteasome activity and estrogen signaling in breast cancer

Estrogen receptor-α (ERα) is a major therapeutic target of hormonal therapies in breast cancer, and its expression in tumors is predictive of clinical response. Protein levels of ERα are tightly controlled by the 26S proteasome; yet, how the clinical proteasome inhibitor, bortezomib, affects ERα regulation has not been studied. Bortezomib selectively inhibits the chymotrypsin-like activity of the proteasome. Unlike other laboratory proteasome inhibitors, bortezomib failed to stabilize ERα protein at a dose exceeding 90% inhibition of the chymotrypsin-like activity. Unexpectedly, however, chronic bortezomib exposure caused a reduction of ERα levels in multiple ER+ breast cancer cell lines. This response can be explained by the fact that bortezomib induced a dramatic decrease in ERα mRNA because of direct transcriptional inhibition and loss of RNA polymerase II recruitment on the ERα gene promoter. Bortezomib treatment resulted in promoter-specific changes in estrogen-induced gene transcription that related with occupancy of ERα and RNA polymerase II (PolII) on endogenous promoters. In addition, bortezomib inhibited estrogen-dependent growth in soft agar. These results reveal a novel link between proteasome activity and expression of ERα in breast cancer and uncover distinct roles of the chymotrypsin-like activity of the proteasome in the regulation of the ERα pathway.

Forkhead Box A1 (FOXA1) is a Key Mediator of Insulin-like Growth Factor I (IGF-I) Activity

The insulin‐like growth factor receptor (IGF‐IR) has been implicated in a number of human tumors, including breast cancer. Data from human breast tumors has demonstrated that IGF‐IR is over‐expressed and hyper‐phosphorylated. Additionally, microarray analysis has shown that IGF‐I treatment of MCF7 cells leads to a gene signature comprised of induced and repressed genes, which correlated with luminal B tumors. FOXA1, a forkhead family transcription factor, has been shown to be crucial for mammary ductal morphogenesis, similar to IGF‐IR, and expressed at high levels in luminal subtype B breast tumors. Here, we investigated the relationship between FOXA1 and IGF‐I action in breast cancer cells. We show that genes regulated by IGF‐I are enriched for FOXA1 binding sites, and knock down of FOXA1 blocked the ability of IGF‐I to regulate gene expression. IGF‐I treatment of MCF7 cells increased the half‐life of FOXA1 protein and this increase in half‐life appeared to be dependent on canonical IGF‐I signal transduction through both MAPK and AKT pathways. Finally, knock down of FOXA1 led to a decreased ability of IGF‐I to induce proliferation and protect against apoptosis. Together, these results demonstrate that IGF‐I can increase the stability of FOXA1 protein expression and place it as a critical mediator of IGF‐I regulation of gene expression and IGF‐I‐mediated biological responses. J. Cell. Biochem. 113: 110–121, 2012.

The estrogen receptor alpha nuclear localization sequence is critical for fulvestrant-induced degradation of the receptor

Fulvestrant, a selective estrogen receptor down-regulator (SERD) is a pure competitive antagonist of estrogen receptor alpha (ERα). Fulvestrant binds ERα and reduces the receptors half-life by increasing protein turnover, however, its mechanism of action is not fully understood. In this study, we show that removal of the ERα nuclear localization sequence (ERΔNLS) resulted in a predominantly cytoplasmic ERα that was degraded in response to 17-β-estradiol (E2) but was resistant to degradation by fulvestrant. ERΔNLS bound the ligands and exhibited receptor interaction similar to ERα, indicating that the lack of degradation was not due to disruption of these processes. Forcing ERΔNLS into the nucleus with a heterologous SV40-NLS did not restore degradation, suggesting that the NLS domain itself, and not merely receptor localization, is critical for fulvestrant-induced ERα degradation. Indeed, cloning of the endogenous ERα NLS onto the N-terminus of ERΔNLS significantly restored both its nuclear localization and turnover in response to fulvestrant. Moreover, mutation of the sumoylation targets K266 and K268 within the NLS impaired fulvestrant-induced ERα degradation. In conclusion, our study provides evidence for the unique role of the ERα NLS in fulvestrant-induced degradation of the receptor.

Proteomic Screening and Lasso Regression Reveal Differential Signaling in Insulin and Insulin-like Growth Factor I (IGF1) Pathways

Insulin and insulin-like growth factor I (IGF1) influence cancer risk and progression through poorly understood mechanisms. To better understand the roles of insulin and IGF1 signaling in breast cancer, we combined proteomic screening with computational network inference to uncover differences in IGF1 and insulin induced signaling. Using reverse phase protein array, we measured the levels of 134 proteins in 21 breast cancer cell lines stimulated with IGF1 or insulin for up to 48 h. We then constructed directed protein expression networks using three separate methods: (i) lasso regression, (ii) conventional matrix inversion, and (iii) entropy maximization. These networks, named here as the time translation models, were analyzed and the inferred interactions were ranked by differential magnitude to identify pathway differences. The two top candidates, chosen for experimental validation, were shown to regulate IGF1/insulin induced phosphorylation events. First, acetyl-CoA carboxylase (ACC) knock-down was shown to increase the level of mitogen-activated protein kinase (MAPK) phosphorylation. Second, stable knock-down of E-Cadherin increased the phospho-Akt protein levels. Both of the knock-down perturbations incurred phosphorylation responses stronger in IGF1 stimulated cells compared with insulin. Overall, the time-translation modeling coupled to wet-lab experiments has proven to be powerful in inferring differential interactions downstream of IGF1 and insulin signaling, in vitro.

Gene Targets of Insulin-Like Growth Factor-I Receptor (IGF-IR) Signaling and Their Potential Role in Breast Cancer.

BACKGROUND: Insulin-like Growth Factor-I Receptor (IGF-IR) has been implicated in a number of human tumors including breast cancer. IGF-IR is over-expressed and potentially hyper-phosphorylated in breast cancer. The specific gene targets of the IGF-IR signaling pathway, and the role of these genes in the development and progression breast cancer is not known.METHODS: MCF7B breast caner cells, and MCF10A immortalized mammary epithelial cells were treated with either serum-free medium or serum-free medium plus 100 ng/ml IGF-I for 3 hours and 24 hours. RNA was isolated and hybridized to U133A Affymetrix microarrays. Candidate genes were selected based on fold change and p-value. Q-RT-PCR was used to validate expression of potential candidate genes. 5,6-Dichlorobenzimidazole 1-β-D-ribofuranoside (DRB) was used (50µM) to block transcription. Cycloheximide (CHX) (20µg/mL) was used to block translation.RESULTS: Data from the microarray revealed 3673 and 3727 genes that were regulated by IGF-I treatment in MCF7B and MCF10A cells, respectively, at 3 hours. Various genes have been validated by Q-RT-PCR, and of these, Suppressor of Cytokine Signaling 2 (SOCS2) SOCS2 was repressed by IGF-I in MCF7B cells, but induced by IGF-I in MCF10A cells. The repression of SOCS2 by IGF-I was inhibited by pretreatment of MCF7B cells with a small molecule inhibitor of IGF-IR, but not by knockdown of IGF-IR by siRNA. This suggests that the repression of SOCS2 is specific to IGF-I signaling, but may be occurring through IGF-I stimulation of an alternate pathway other than IGF-IR. IGF-I doesn9t alter levels of SOCS2 mRNA following blockade of transcription, suggesting that IGF-I does not have an effect on SOCS2 mRNA stability. Furthermore, IGF-I-mediated repression of SOCS2 does not require new protein synthesis, and is thus likely an immediate and direct response.CONCLUSION: SOCS2 is a candidate tumor suppressor gene in breast cancer, with loss of SOCS2 being related to cell proliferation and tumor growth. Here we show that SOCS2 is one of the gene targets of IGF-I signaling and is repressed by IGF-I stimulation in MCF7B breast cancer cells. Furthermore, the repression of SOCS2 by IGF-I appears to be via a direct inhibition of transcription. Together, this suggests that SOCS2 is a direct gene target of IGF-I signaling and that IGF-I repression of SOCS2 may be a crucial event that plays a role in driving the development or progression of breast cancer. Further studies are planned to determine how IGF-I affects SOCS2 function and the role of SOCS2 in breast cancer. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 4167.

Abstract 4133: Comparative gene expression and proteomic analysis of IGF-I and insulin signaling in a large panel of breast cancer cell lines

IGF-I signaling is involved in tumor progression and drug resistance and many anti-IGF-IR therapeutic agents are currently in clinical trials. Moreover, growing evidence also suggests that insulin signaling may play an important role in cancer development and progression. However, little is known regarding similarities and difference in IGF-I and insulin signaling in cancer, and there are currently no biomarkers to predict patient response to IGF targeted therapy. To gain a better understanding of these signaling pathways in human breast cancer, we measured the levels of insulin receptor (IR) and IGF-IR, and the activity of insulin and IGF-I, in a large panel of human breast cancer cell lines. Comparative gene expression analysis was performed using publicly available gene expression data and IR and IGF-IR mRNA levels in 17 breast cancer cell lines were measured by Q-RT-PCR. IGF-IR and IR levels were found to be highly variable in breast cancer cell lines. MCF7 and MDA-MB-134 have high levels of IGF-IR expression and MDA-MB-468 and ZR-75-1 have high levels of IR expression, relative to other breast cancer cell lines. Reverse phase protein array (RPPA) analysis using 134 different antibodies was performed on MCF7 cells stimulated with increasing doses of insulin or IGF-I. One Way ANOVA was performed to identify proteins affected by insulin and/or IGF stimulation. Maximal response to insulin and IGF-I stimulation was observed at a 10nM concentration of both ligands. Therefore, we further performed RPPA on 21 breast cancer cell lines treated with 10nM of insulin and IGF-I for 6 time points (5min, 10min, 30 min, 6hrs, 24hrs, and 48hrs). Spearman rank correlation was performed on IR and IGF-IR protein levels to mRNA levels from Q-RT-PCR. There was a significant correlation between IGF-IR protein and mRNA levels (r=0.559, p=0.024), but not between IR protein and mRNA levels. Principle component analysis showed that MCF7, MDA-MB-134, T47D and ZR-75-1 are insulin and IGF-I responsive. Results from ANOVA with contrast in MCF7 cells showed that insulin and IGF-I affected similar set of proteins at 10 minute and 24 hours time points, however, there were several proteins affected only by IGF-I or insulin stimulation. For example, phospho-estrogen receptor (p-ER) was found to be increased by 10 minutes IGF-I stimulation, but not by insulin stimulation. Beta-catenin and c-Myc were significantly suppressed by IGF stimulation while PARP was significantly suppressed by insulin stimulation at the 24 hour time point. Moreover, IGF affected twice the number of proteins compared to insulin at the 48 hour time point. For instance, Bcl2 and SMAD3 were suppressed and Raf and FOXO3a were increased by IGF stimulation after 48 hours of stimulation. Further statistical and system biology analysis of the temporal activation of signaling by IGF-I and insulin in the 21 cell lines is ongoing and will be presented. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4133.

Evidence for Unique Mechanisms of Estrogen Receptor Degradation Elicited by Estradiol and ICI 182,780 (Fulvestrant).

Selective estrogen receptor down-regulators (SERDs), such as ICI 182780 (Fulvestrant), comprise a class of drugs that has been developed to inhibit estrogen receptor alpha (ER) activity in breast cancer. ICI is a pure antagonist that competitively binds to the ligand-binding domain of ER. The binding of ICI is thought to reduce the receptor9s half-life by increasing protein turnover. However, the exact mechanism of ICI action, including whether or not receptor degradation is actually required for its antiestrogenic action, is currently unknown. Our laboratory has shown that a cytoplasmic ER mutant (ERΔNLS) lacking a nuclear localization sequence (NLS) is completely resistant to ICI-mediated degradation in both MCF-7 breast cancer cells and their ER-negative derivatives, C4-12 cells. Immunofluorescence and confocal microscopy were performed to assess localization of all ER proteins. These cells were also treated for different lengths of time with varying concentrations of both estradiol (E2) and ICI. Immunoblotting was performed to determine levels of ER protein. A competitive radioligand binding assay was also conducted to assess the ligand-binding capability of the ERΔNLS mutant receptor. Immunofluorescence and confocal imaging of stably transfected C4-12 cells has confirmed distinct subcellular localization of each ER protein. Wild-type ER localizes mainly to the nucleus, while ERΔNLS is cytoplasmic. As expected, treatment of either wild-type MCF-7 cells or C4-12 cells expressing wild-type ER with E2 or ICI caused degradation of ER protein. Treatment of MCF-7/ ERΔNLS or C4-12/ ERΔNLS cells with E2 caused degradation of ERΔNLS protein. In stark contrast, increasing concentrations of ICI failed to cause degradation of ERΔNLS. Furthermore, experiments performed in the presence of cycloheximide have shown that ICI does not modulate ERΔNLS half-life. The inability of ICI to degrade ERΔNLS is not due to an inability of ERΔNLS to bind ligand, since results from competitive radioligand binding assays show that the affinity of ERΔNLS for both E2 and ICI is equal to the affinity of wild-type ER for both ligands. We have recently cloned the SV40-NLS onto ERΔNLS, and confocal microscopy has confirmed that the SV40-NLS is sufficient to force ERΔNLS into the nucleus. I am currently using this construct to determine if it is the NLS domain itself or merely subcellular localization of ER that is important for ICI-mediated degradation. In conclusion, ER is a critical marker for response to antiestrogen therapy. Treatment with ICI is not without its shortcomings. A better understanding of the mechanism by which ICI degrades ER may lead to the development of better antiestrogen therapies to inhibit ER action with less toxicity and greater specificity. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 4137.

JNK, essential for anticancer therapy-induced apoptosis, promotes breast cancer progression.

CTRC-AACR San Antonio Breast Cancer Symposium: 2008 Abstracts Abstract #5075 The c-Jun N-terminal kinase (JNK) is a critical mediator of stress-induced apoptosis and is required for the cytotoxic effect of anticancer therapies. Interestingly, recent clinical studies showed that high JNK activity is associated with poor prognosis in human breast cancer. The molecular basis of this potential dual function of JNK in breast cancer is poorly understood. Here we report that overexpression of a constitutively active JNK in breast cancer cells increased cell migration and invasion. In agreement with this, fibroblast-specific markers like the intermediate filament vimentin and the extracellular matrix protein fibronectin were up-regulated. AP-1 transcription factor, which induces expression of these two proteins, was markedly increased by JNK overexpression. In addition, hyperactive JNK reduced Akt1 activation but enhanced Erk activation in breast cancer cells. In relevance, we also found that JNK levels are significantly higher in invasive breast cancers including those with distant metastases (n = 235, p < 0.0001, Wilcoxon rank sum test) than in normal breast tissues (n = 69). Most surprisingly, an increase of JNK attenuated the apoptosis of breast cancer cells treated with chemotherapy drugs doxorubicin and taxol. This suggests that the role of JNK changes when its activity/expression increases above the basal levels associated with apoptosis. Our data, together with a recent finding that cells undergoing cytotoxic agent-induced apoptosis can induce compensatory hyper-proliferation of proximal cancer cells, suggest a novel mechanism of breast cancer therapeutic resistance. Therapy-elicited apoptosis of tumor cells with basal JNK activity may release mitogens that induce hyperactive JNK in neighboring cells to promote growth and invasion. Thus JNK activation may serve as a marker of breast cancer progression. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 5075.