Our Current Trainees
The Cancer Biology Training Grant currently has funding for four predoctoral trainees and five postdoctoral trainees.Faculty preceptors are notified when a slot becomes available and a competitive application process is held. Applicants are evaluated and trainees selected by the training grant steering committee.
Breast cancer remains the most frequently diagnosed cancer and the second leading cause of cancer-related death in American women. Current targeted therapies exist for tumors that are estrogen receptor (ER)/progesterone receptor (PR) positive and tumors with an amplification of the growth factor receptor HER2. However, tumors lacking ER/PR expression and without an amplification of HER2, referred to as triple-negative breast cancer (TNBC), have no targeted therapy options and must instead be treated with systemic chemotherapy and surgery. TNBC are also among the most aggressive subtypes of breast cancer and have an accordingly poor prognosis. These factors demonstrate the important need to develop novel therapeutic strategies against TNBC.
Recent interest has also focused on the contributions of inflammation to TNBC. Specifically, tumors with high numbers of infiltrating macrophages are associated with poor patient prognosis and it has been demonstrated that TNBC have increased macrophage recruitment compared to other breast cancer subtypes. Experimental studies show that tumor-associated macrophages (TAMs) promote tumor growth and metastasis. However, it is unclear what factors regulate TAM function and the mechanisms by which TAMs support tumorigenesis.
The goal of my research is to uncover the mechanisms by which TAMs promote tumor formation in TNBC. Using a mouse model of TNBC, we have found that: 1) TAMs are required for the formation of hyperplastic lesions, angiogenesis and invasion, and 2) soluble factors from TNBC cells activate signaling pathways in TAMs that lead to a pro-tumor response in the macrophages. The successful completion of these studies will identify new drug targets for the treatment of TNBC and other TAM-driven malignancies as well as provide new insight into the regulation and function of TAMs.
Ovarian cancer is the most deadly disease of the female reproductive tract. Due to ineffective therapeutics and large amounts of tumor heterogeneity, ovarian tumors are associated with poor outcomes and high rates of recurrence following treatment. It is widely accepted that the tumor heterogeneity seen in ovarian cancer is due to a high degree of genomic instability, which drives many ovarian tumorigenic phenotypes. Therefore, our lab is interested in defining the underlying sources of genomic instability in cancer. We have recently identified the highly active, nuclear DNA cytosine deaminase, APOBEC3B, as a major source of mutation in several distinct carcinomas including ovarian cancer. This enzyme belongs to an 11-member family of proteins that is capable of catalyzing C-to-U deamination events in DNA that can lead to mutations during DNA synthesis and error-prone repair. My early thesis work has focused on defining the role of APOBEC3B in ovarian cancer. So far, I have shown that A3B is the only cytosine deaminase significantly up-regulated in ovarian cancer cell lines. In addition, I have found that APOBEC3B is similarly up-regulated in primary human tumors and correlates positively with mutation loads in a subset of these samples. My current work aims to better understand the specific DNA repair pathways that are responsible for the repair of the uracil lesions created by APOBEC3B in cancer cells.
Lung cancer remains the most common cause of death from cancer in the US and there is a high need for improved therapeutic interventions. Epidermal growth factor receptor (EGFR) is a major target for the treatment of NSCLC, but only a subset of patients with EGFR mutations benefit from EGFR tyrosine kinase inhibitors (TKIs) such as erlotinib (an FDA-approved drug). Intrinsic lack of response to erlotinib and development of acquired resistance are driven by mechanisms not fully understood. This proposal seeks to develop and implement a combination therapy that will be beneficial to NSCLC patients with or without EGFR mutations. The goal is to combine erlotinib with a molecule that targets an important downstream mediator common to EGFR, and other TKIs. Signal transducer and activator of transcription (Stat3) is a key mediator of EGFR signaling and other tyrosine kinase receptors (RTKs). Targeting the EGFR/STAT3 axis in a combination therapy is an intriguing idea that could allow for a broader effect not solely dependent on EGFR mutation status.
This proposal seeks to determine whether the anti-tumor activity of the FDA approved TKI erlotinib can be enhanced through pharmacological inhibition of STAT3. A cyclic oligonucleotide molecule with a novel mechanism that acts as a STAT3 “decoy” will be tested in combination with erlotinib in NSCLC. The “decoy” mimics the DNA consensus sequence in the promoter region of STAT3-responsive genes, causing the binding of phosphorylated STAT3 dimers and preventing their nuclear translocation. Evidence shows that STAT3 is persistently activated in 22% - 65% of NSCLC and overexpression of phosphorylated STAT3 (pSTAT3, the active form of Stat3) is associated with poor prognosis. This project could therefore be of major significance because the potential of the cyclic Stat3 decoy (CS3D) to treat NSCLC is high (given that pStat3 is overexpressed in NSCLC), and the CS3D has not yet been tested for the treatment of NSCLC.
The proposed research is relevant to public health because it will help identify lung cancer patients appropriate for treatment with a novel therapeutic that targets Stat3, an important oncogenic molecule. This proposal also will determine whether a Stat3 inhibitor can be combined with erlotinib, an FDA-approved drug for the treatment of lung cancer.
Genomic instability is a hallmark of cancer. The focus of the Sobeck laboratory is to understand how human cells maintain genomic stability. Fanconi anemia (FA) is a multi-gene genome instability disease associated with a strong cancer predisposition. Inherited and sporadic FA gene defects are associated with various cancers including leukemia and solid tumors such as head and neck, breast and pancreatic cancers. The FA genes participate in the repair of DNA interstrand crosslinks (ICLs) that covalently link two DNA strands and thus block DNA replication and transcription. ICLs are caused by endogenous metabolic intermediates, but also by chemotherapeutic agents such as cisplatin. FA research has therefore two main objectives: 1) to understand how FA gene defects lead to DNA repair deficiencies and drive tumorigenesis and 2) to understand how cancer patients with wild type or mutated FA genes tolerate DNA lesions caused by chemotherapeutic agents.
The key player in the FA pathway is the FANCD2 protein. FANCD2 has crucial roles in ICL repair but the underlying mechanisms are only partially understood. Following ICL induction, FANCD2 is recruited to chromatin by the ataxia telangiectasia-Rad3-related (ATR) kinase. ATR responds to DNA damage such as ICLs by phosphorylating hundreds of downstream proteins - including FANCD2 and the checkpoint kinase CHK1 - at serine or threonine residues in an SQ/TQ context. These phospho-events are thought to promote the cellular DNA damage response by coordinating mechanisms such as DNA repair and cell cycle control, but the functions of most of these phosphorylation events are unknown. Unexpectedly, I found that the ATR-mediated CHK1 phosphorylation in response to DNA ICLs is strongly reduced in FANCD2-deficient cells. This suggests a step-wise mechanism where FANCD2 is recruited by ATR to DNA ICLs, where it then functions to regulate ATR kinase activity. Based on these data, I hypothesize that FANCD2 has a new function during ICL repair: it controls ATR kinase activity to promote phosphorylation of downstream DNA repair factors. I predict that this role of FANCD2 is crucial for efficient DNA ICL repair. To test this hypothesis, I am using a proteomics approach to identify ICL-induced, ATR-mediated phosphorylation events on target proteins that are regulated by FANCD2. Furthermore, I am characterizing the importance of their phosphorylation for ICL repair.
Ryan Baxley, Ph.D.
The overall goal of the Bielinsky laboratory is to understand how human cells maintain a stable genome. Current evidence suggests that multiple pathways converge in a genome stability network that shields cells from chromosome breakage by either preventing DNA damage or facilitating repair. Double-strand breaks (DSBs) are a severe form of DNA damage, such that defects in DSB repair proteins predispose individuals to cancer. One crucial factor in the only error-free DSB repair pathway, homologous recombination (HR), is the breast cancer type 2 susceptibility (BRCA2) gene. Germ line mutations in BRCA2 cause hereditary breast and ovarian cancers. BRCA2 encodes a 3,418 amino acid protein with a centrally conserved domain of eight BRC repeats that bind to Rad51, a protein required to initiate HR. In addition, BRCA2 has been implicated in preserving the integrity of stalled replication forks and preventing fork collapse, which generates DSBs. While the exact role of BRCA2 at stalled forks remains unknown, the Bielinsky lab found that BRCA2 interacts with the essential replication factor minichromosome maintenance protein 10 (Mcm10). Mcm10 is part of the BRCA1-PALB2 (partner and localizer of BRCA2)-BRCA2 complex, in which Mcm10 and BRCA2 directly interact and do not require PALB2 or BRCA1 to mediate binding. Multiple genome-wide genetic screens have identified human Mcm10 as a major player in DNA damage prevention, consistent with its role as a scaffold protein that connects different fork components. Mcm10 may preserve genome integrity simply by stabilizing fork complexes. However, in the light of the interaction with BRCA2, another possibility is that Mcm10 has a direct role in recruiting BRCA2 to stalled replication forks to prevent fork collapse and chromosome breakage. Preliminary data suggests that an N-terminal coiled coil motif in Mcm10 serves as the binding surface for a subset of specific BRC repeats in BRCA2. My studies will characterize the interaction between Mcm10 and BRCA2 and investigate how cancer associated mutations in the BRCA2 BRC motifs affect this interaction. Further, I will generate a human cell line that expresses mutant Mcm10 defective for BRCA2 binding. This will allow me to investigate if Mcm10 is required for BRCA2 recruitment to stalled forks and whether this interaction plays a significant role in suppressing chromosome breakage.
Katherine Leehy, Ph.D.
Progesterone binds to PR (progesterone receptor) causing dimerization and localization in the nucleus where it binds to progesterone response elements (PREs) or is tethered to other transcription factors. In the normal mammary gland PR/progestins facilitates development by mediating the massive expansion of breast tissue that occurs during puberty and pregnancy to facilitate lactation. While PR is only present in 7-10% of normal breast tissue where it initiates both paracrine and autocrine signaling to enhance proliferation, it is expressed in up to 70% of breast cancers. Recent in vitro mechanistic studies by our group and others demonstrated that PR is capable of driving breast cancer progression in both the absence and presence of progestin. Activation of PR by kinase mediated phosphorylation events increases cellular proliferation and anchorage independent cell survival. Notably, breast tumors that express a phospho-PR gene signature are predicted to have a poor prognosis. Moreover, large-scale clinical trials examining hormone replacement therapies containing estrogen and progestin showed that progestins increased breast cancer risk and tumor aggressiveness in women relative to estrogens alone. Recent interest in the use of antiprogestins as therapeutics for steroid receptor positive breast cancers further emphasizes the importance of understanding the mechanisms by which PR promotes breast cancer and may prove critical to determining which patients will benefit most from targeting PR and PR associated pathways.
PR is an important mediator of breast cancer development and progression. In particular, PR is activated during cell cycling and interacts with many components of the cell cycle regulation machinery. Direct interactions between PR and cyclins A, D and E have been observed. There are a number of phosphorylation sites on PR that are induced by kinases cdk2, ck2 and MAPK that affect its transcriptional activity. In addition, many cancers upregulate MAP kinase activity and down regulate cell cycle inhibitors, which functions to further activate PR transcriptional programs. Therefore, we speculate that loss of checkpoint controls as early events in breast cancer may push PR into a hyperactive state that drives breast cancer progression.
p53 is the most commonly mutated gene in human cancer, and both loss of expression and mutations in p53 are associated with malignancy. Interestingly, mutations in p53 can have a pro-oncogenic effect as cells become resistant to apoptosis. Loss of active p53 is present in half of all breast cancers. These changes allow the cells to divide continuously without cell cycle inhibition and in the absence of normal growth factors. Interestingly, parity has been shown to protect against breast cancer in part by upregulation of p53 and p21 in luminal (SR +) mammary cells. Additionally, treatment with of anti-progestins prevents mammary tumor formation p53 null/BRAC1 mice, suggesting a potential link between DNA damage control, cell cycle regulation, and hormone action. Therefore, investigating the effects of loss/mutation of p53 on PR expression and regulation is an important step to help determine/optimize alternate breast cancer therapy.
We hypothesize that PR is a major driver of cancer progression by changes in phosphorylation status and thru interaction with cell cycle components. PR and p53, a master cell cycle regulator, act together to initiate tumor development and facilitate progression of breast cancer. My project will examine how changes in cell cycle regulation affect PR. 1) Determine the effect of p53 loss/mutation on regulation of PR isoforms. 2) Determine the effects of changes in p53 status on progestin-driven proliferation and pro-survival in ER+/PR+ breast cancer cell lines. 3) Determine how these changes effect tumors in mice with and without progestin treatment. . These experiments will determine the effects of p53 mutation in PR+ cells on tumor formation/progression and demonstrate the potential for use of anti-progestin treatments that may block hormone-dependent growth pathways in luminal (ER+/PR+) breast cancer.
Kristin Renkema, Ph.D.
Melanoma is the most aggressive skin cancer and affects 2% of the entire American population. Anti-tumor CD8 T cells can control melanoma, but developing a strong and suitable CD8 T cell response is inefficient by current methods. Here we study a novel approach for inducing tumor-specific CD8 T cells in a mouse model of melanoma.
CD8 T cells express unique T cell receptors (TCR) that recognize a peptide bound to MHC Class I (MHC-I) molecules. Tyrosine-related protein-2 (Trp2) – a melanocyte enzyme over-expressed in melanoma – encodes a peptide that can be seen by CD8 T cells. T cells that recognize such “self” peptides are typically killed in the thymus or held in check by regulatory mechanisms – however, Trp2 specific CD8 T cells arise in healthy mice (and humans), and when sufficiently activated can eliminate melanoma. However, current methods fail to induce a strong CD8 T cell response to the Trp2 peptide in mice, limiting potential for this approach in humans.
Recent studies suggest peptide-binding affinity for MHC-I is critical for generating strong anti-tumor CD8 T cell responses; we hypothesize that improving the stability of the Trp2-MHC-I interaction will improve priming of potent anti-melanoma CD8 T cells. “Single chain trimers” (SCT) covalently link a peptide to the MHC-I molecule: This structure is very stable yet effective primes antigen specific CD8 T cells which protect against pathogen infection. We propose using Trp2 SCT to prime anti-melanoma CD8 T cells and determining whether the resulting CD8 T cell response can control B16 melanoma cancer in mice. If Trp2 SCT improves anti-melanoma CD8 T cell responses, the approach could be developed for future application in humans. In addition, our observations may lead to future studies on functional tolerance of self-specific Trp2 specific CD8 T cells, regardless of Trp2 SCT priming efficacy.
Jamie Van Etten, Ph.D.
Kyle Williams, Ph.D.