Research Grants Awarded
Tumor-Associated Macrophage-Mediated Inflammatory Responses In Serm "Resistant" Breast Cancer As A Therapeutic Target
Defining the molecular mechanisms of anti-hormone resistance in breast cancer lies at the center of basic breast cancer research. The functional significance of recent identified tumor-associated macrophages makes it important to explore new strategies to understand and prevent anti-hormone resistance. Our laboratory indicated that tumor associated macrophages may induce androgen and estrogen target gene activation and mediate the switch in function of Selective Androgen/Estrogen Receptor Modulators (SARMs/SERMs) from antagonists to agonists. The peroxisome proliferator-activated receptor gamma (PPAR-gamma), and Livder X receptors alpha/beta (LXR alpha/beta) are both expressed in macrophages and can negatively regulate the program of macrophage activation by repressing distinct subsets of AP-1 and NF-kappa B-dependent genes. Therefore, I hypothesize that tumor-associated macrophages drive inflammatory programs of gene expression to affect SERMs resistance can be blocked by ligands of LXRs and PPAR gamma, which act as inhibitors of these events, in part, by counter-regulating initial inflammatory responses in macrophages. The NCoR/SMRT corepressor complexes (and other corepressor complexes) are required for LXR/PPAR-gamma-mediated repression of inflammatory response genes.
Another intriguing target is G-protein pathway suppressor 2 (GPS2) and related protein KIAA1787. Removal of GPS2 and KIAA1787 by validated siRNAs is sufficient to activate target genes of multiple nuclear receptors in the absence of hormone stimuli, suggesting that GPS2 and KIAA1787 may serve as a negative checkpoint for hormone dependency. Thus, I further propose that the SERM resistance is at least partially mediated via the novel negative regulator GPS2 and related protein KIAA1787 by inhibiting protein kinase-dependent signaling pathways, thereby maintaining hormone dependency on ER.
I will address these hypotheses by pursuing two specific aims. Aim1: To investigate the regulation of LXR/PPAR gamma-dependent gene targets in repression of activated macrophages and signaling pathways that result in hormone resistance in breast cancer. I will take advantage of high throughput genome-wide technologies coupling chromatin-immunoprecipation with Solexa single-molecule sequencing (referred as ChIP-Seq) for genome-wide analysis and RNA quantification, which is available in our laboratory to systematically investigate the PPAR-gamma and LXR-regulated gene networks in macrophages and whether this transrepression of inflammation requires the corepressor complexes, NCoR/SMRT, with NCoR-/- and SMRT-/- macrophages generated from our laboratory. Aim2: To explore the potential actions of the NCoR-associated corepressor factor, GPS2 and related protein KIAA1787, as a mechanism for constitutive activation of Estrogen Receptor (ER)-regulated gene targets in SERM ?resistant? tumors. The experiments are designed to identify the GPS2- and KIAA1787-dependent gene networks and upstream signaling pathways.
Taken together, the proposed study will explore two aspects of resistance in breast cancer by studying a new aspect of transrepression of macrophage inflammation response gene and the roles of a potent coregulator that prevents estrogen-independent gene activation. These findings will provide an alternative target for drugs inhibiting activation of tumor-associated macrophages and shed light on the transcriptional regulation events in SERMs resistant breast cancer that have a number of intriguing therapeutic implications. Based on extensive preliminary data, I am confident that these specific aims can be accomplished during the three year period of award.
Estrogen is essential for the physiological function and growth of the mammary gland, and anti-estrogen treatment, which blocks the expression of estrogen target genes, is widely used for the treatment of breast cancer. Unfortunately, many patients eventually progress to a hormone independent form of cancer, which then becomes a key cause underlying the high death rate of breast cancer. Findings of our laboratory about the role of inflammatory response on the function of anti-hormone resistance form the basis of this proposal.
Recruitment of tumor-associated macrophages is correlated to poor prognosis in many solid tumor types. In breast cancer, tumor-associated macrophages stimulate the invasive and malignant capacities of cancer cells, situating chronic inflammation as an important cofactor in the promotion of tumors. The underlying connection between inflammation and resistance to particular cancer drugs makes it important to explore new strategies to understand and prevent drug resistance. To mechanically define the role of macrophages in cancer progression and anti-hormone resistance is the core of the proposal and holds the promise of new therapeutic targets for breast cancer. Here, I propose to pursue two approaches to this issue, each based on intriguing and compelling preliminary data. Infiltrating macrophages and cancer cells interact, eliciting macrophage-secreted inflammatory cytokines to activate a pathway to block the actions of 4-OHT. Our laboratory has found that the peroximsome proliferator-activated receptor gamma (PPAR-gamma) and liver X receptors (LXRs) both expressed in macrophages, can repress distinct, but overlapped macrophage gene activation processes, providing one tempting target for therapeutic intervention to block hormone resistance. Therefore, it is important to investigate the inflammatory programs of gene expression blocked by ligands of LXRs and PPAR-gamma, which counteract the initial inflammatory response in macrophages. I will take advantage of high throughput genome-wide technologies, coupling chromatin-immunoprecipation with the Solexa single-molecule sequencing (referred as ChIP-Seq), which is available in our laboratory to systematically investigate the PPAR-gamma and LXR-regulated gene networks in macrophages both by certain antibodies and mRNA quantification to define whether transrepression of the inflammation gene programs requires specific untested components of NCoR/SMRT corepressor complexes, utilizing NCoR-/- and SMRT-/- macrophages that has been generated from our laboratory.
The second approach centers on identifying new components of nuclear receptor corepressor complexes that block the expression of estrogen targeted gene expression in the presence of anti-hormone treatment. These experiments are designed to identify new targets for better understanding clinical resistance to Selective Estrogen Receptor Modulators (SERMs). Our laboratory has identified a recently recognized additional component of the NCoR complex, acting as a negative regulator of diverse signaling pathways. Removal of this negative regulator results in inappropriate gene activation in the absence of activation stimuli, leading to potential cancer progression and drug resistance. Experiments designed to understand the role of this novel component of the NCoR complex in constitutive activation of estrogen receptor (ER) target genes and SERM resistance in breast cancer are therefore likely to uncover useful strategies to improve the outcome of anti-hormone therapy.
In summary, increasing evidence suggests that the activity of infiltrating macrophages represents an important clinical aspect of breast cancer therapeutics. The proposed study in this application will provide quantitative, digital and real-time database information used for identification of new targets of cancer therapy, new insights into the hormone resistance and sex steroid receptor independence in breast cancer, and additional strategies to modify therapeutic approaches to breast cancer.