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.
Tarah Regan Anderson
Despite advances in targeted therapies, breast cancer remains the second leading cause of cancer related death in women in the United States. Our research therefore focuses on identifying signaling pathways critical to breast cancer progression that may be exploited for novel therapies. Breast tumor kinase (Brk/PTK6) is a soluble tyrosine kinase that is aberrantly expressed in 86% of breast cancers. Brk is known to signal downstream of a diverse group of growth factor receptors, including epidermal growth factor receptor (EGFR), Her2, and Met receptors. Moreover, Brk signaling leads to enhanced invasion and metastasis of breast cancer cells in vitro. Our current research focuses on understanding the mechanism governing aberrant Brk overexpression in breast cancer cells, particularly in triple negative breast cancers (TNBC), as this subtype lacks expression of the molecules currently exploited for targeted therapy (estrogen receptor, progesterone receptor, Her2). We recently discovered a novel mechanism regulating Brk expression under conditions of cell stress. Hypoxic cell stress, which is abundant in solid tumors, results in increased levels of Brk mRNA and protein. Moreover, we have identified Brk to be a novel transcriptional target of hypoxia inducible transcription factors, HIF-1α and HIF-2α. Notably, we showed by development of a transgenic mouse model (Brk x METMut) that activated Brk signaling in the mammary gland decreases tumor free survival.
We plan to thoroughly characterize the molecular factors driving the Brk promoter in response to cell stress. Preliminary data suggest that the glucocorticoid receptor (GR) is also involved in upregulating Brk expression following dexamethasone treatment, potentially suggesting crosstalk between cell stress and cortisol signaling pathways. Additionally, we are interested in the mechanisms by which Brk activates signaling pathways downstream of growth factor receptors. We will investigate the functional domain requirements for Brk-dependent propagation of oncogenic signaling pathways. These studies will provide mechanistic insight into novel pathways that may be targeted for patients with TNBC and other cancers in which Brk is also overexpressed.
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.
Cancer cells generate elevated levels of oxidative stress during proliferation that is tolerated more readily than in healthy cells. The mechanisms that lead to reduced oxidative stress and apoptosis inhibition are understood in cancer but the nature of their integration remains elusive. For example, glycolysis inhibition can lead to a redirection of glucose into the pentose phosphate pathway that results in the synthesis of the reductive molecule NADPH. Cancer cells exploit this pathway through the targeted inhibition of a variety of glycolytic enzymes. In addition, anti-apoptotic proteins are over-expressed in the vast majority of cancers leading to a generalized resistance to apoptosis. Oxidative stress signaling in cancer is less understood. It has been shown that cancer cells prefer a low level of oxidative stress for proliferation, while the damage sustained to proteins during elevated levels of oxidative stress is detrimental to the cell's survival and requires reductive adaptation. It stands to reason, therefore, that metabolic re-programming, apoptosis inhibition and oxidative stress signaling must be integrated to execute the balance between too little and too much oxidative stress. We have characterized a macromolecular complex that harbors, among other proteins, a core containing a glycolytic enzyme (GAPDH), an anti-apoptotic protein (Mcl-1) and a novel oxidative stress responsive protein (EF1-γ), in acute T cell leukemia. We also detect this core complex in nearly all epithelial malignancies examined. We propose that the association of these three proteins integrates three critical hallmarks of cancer and therefore has the potential to make a significant contribution to our understanding of how proliferating cells suppress apoptosis while adapting to oxidative stress through the redirection of glycolytic intermediates. Furthermore, we propose that this protein complex represents a significant therapeutic target that, upon disruption, could potentially cripple three hallmarks of cancer simultaneously, a particularly important concept given that inhibitors targeted to single pathways often lead to resistance and relapse.
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.
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.
Jenna Benson, Ph.D.
All cells receive signals that can initiate growth or death at appropriate times. When expression of proteins controlling these signals becomes aberrant, uncontrolled expansion of cells can ensue and lead to cancer. The long-term goal of the Kelekar laboratory is to elucidate the roles of these proteins in the survival, death, and metabolic flux of leukemia cells. We recently demonstrated that the atypical glucose-sensitive kinase, Cdk5, phosphorylates human Noxa, switching it from a pro-death to a pro-survival protein in leukemia cells. The putative upstream regulators of this Cdk5 have been extensively studied in the nervous system and are associated with neurodegenerative diseases, such as Alzheimer’s; however, their role(s) in lymphocytes and hematological malignancies have yet to be investigated. Thus, our goal is to better understand how Noxa becomes phosphorylated and consequently promotes hematopoietic cell survival. To this end, my projects address two broad questions: 1) How does Cdk5-mediated Noxa phosphorylation contribute to survival signals in non-malignant as well as cancerous lymphocytes, and 2) Does constitutively expressed human Noxa play both leukemogenic and tumor-suppressor roles in developing lymphocytes? Experiments designed to specifically answer these questions will yield two novel sets of data. First, the mechanism by which this “death” protein imparts a survival function in terms of proliferation and metabolism of rapidly dividing cells will be defined. Second, the development of a conditional transgenic mouse model will allow us to study the role of Noxa in the initiation, progression and maintenance of leukemia. Collectively, these projects will lead to a better understanding of the regulatory mechanisms that promote and sustain the survival of rapidly dividing normal and cancer cells. Targeting these novel mechanisms could eventually lead to the development of more efficacious therapeutics to combat cancer.
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.