This Fox Chase professor participates in the Undergraduate Summer Research Fellowship.
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Professor
Nuclear Dynamics and Cancer Program
Co-Director, Biological Imaging Facility
BRCA biology and therapy resistance
The Johnson laboratory studies mechanisms of DNA damage detection, repair, and signaling that occur in BRCA1 mutation-containing organisms and cancers. We use a range of approaches, including cell biology, mouse genetics, and therapy resistance modeling, to understand basic biological processes and their implications for tumorigenesis and chemotherapy sensitivity.
Dr. Neil Johnson is an associate professor with tenure at Fox Chase Cancer Center (FCCC) and leads an NCI R01-funded research program. Dr. Johnson’s laboratory studies mechanisms of DNA damage detection, repair, and signaling that occur in BRCA1 mutation-containing organisms and cancers. A range of approaches are routinely employed, including cell biology, mouse genetics, and therapy resistance modeling, to understand basic biological processes and their implications for tumorigenesis and chemotherapy sensitivity. In particular, Dr. Johnson’s research has focused on the utility of PARP inhibitor (PARPi) therapy for the past 10 years. Dr. Johnson used small molecule inhibitors to convert homologous recombination (HR) proficient cancer cells into HR-deficient cells, inducing ‘BRCAness’, and sensitizing cancers to PARPi. Subsequently, multiple contributions have been made toward understanding mechanisms by which BRCA1 mutation-containing alleles generate protein products that promote HR repair and chemotherapy resistance. More recently, several new BRCA1 mutant mouse alleles were generated in the Johnson laboratory to study the impact of loss of various BRCA1 functional domains on development and organismal health. Currently, the Johnson laboratory is continuing to explore DNA repair biology, and we aim to improve the current understanding of the role of BRCA1 in the repair of double stranded DNA breaks (DSBs) and maintaining genome stability. Central projects that are available to students are discussed below.
1. Determining the role of BRCA1 protein interactions in DNA repair, development and cancer.
The maintenance of genome integrity is essential for organismal development and preventing DNA damage-linked diseases such as cancer and Fanconi anemia (FA). Mutations in BRCA1 or PALB2 disrupt HR DNA repair and result in genome instability. The BRCA1 and PALB2 proteins directly heterodimerize through their respective coiled-coil (CC) domains, facilitating the formation of a larger BRCA1-PALB2-BRCA2-RAD51 complex that is required for RAD51 filament formation. BRCA1 and PALB2 form the only known interaction that is mediated by either proteins CC domain. Whether BRCA1 and PALB2 CC domains exclusively interact with one another, or there are additional CC interactions and functions is unknown. Because both BRCA1 and PALB2 form multiple protein complexes, specifically disrupting the CC domain is required to discern activities related to the BRCA1-PALB2 heterodimer. Our laboratory has developed novel BRCA1 and PALB2 CC domain mutant mouse models to investigate the significance of this interaction in DNA repair and organismal health. Brca1CCand Palb2CCalleles each have a 3-amino acid deletion in the CC domain that disrupt the BRCA1-PALB2 association but maintain protein stability and non-CC protein interactions. Collectively, we are using biochemical, cell-based, and mouse genetic experiments to evaluate the nature and importance of the BRCA1-PALB2 interaction in DNA repair and maintaining genomic integrity.
2. Identifying new biological mechanisms of BRCA1-associated DNA repair.
An accumulation of DNA breaks or large insertions and deletions can induce loss of cellular and organismal viability, as evidenced by early embryonic lethality observed in Brca1 knockout mouse models. Paradoxically, BRCA1 mutant and wild-type cancers are equally viable and malignant. To sustain viability in the absence of BRCA1, cancers require adaptations that promote the repair of endogenous DNA damage. BRCA1 mutant cancers invariably harbor TP53 mutations, and loss p53 signaling can rescue the embryonic viability of mice harboring hypomorphic Brca1 alleles. However, the embryonic viability of Brca1 null alleles cannot be rescued with Tp53 knockout. Cells harboring more deleterious BRCA1 mutant alleles may require additional epi/genetic alterations to maintain viability. In this project, we are working on novel mechanisms of DNA repair pathway re-wiring that are responsible for sustaining the viability of BRCA1 mutant cancers; with the goal of providing new insights into cellular conditions that foster genome instability and carcinogenesis.
3. Uncovering therapy response determinants in BRCA1-mutation carrying tumors.
Patients with BRCA1 mutations have better therapy response and overall survival outcomes compared to BRCA1 wild-type patients. Mutations located in exon 11 of the BRCA1 gene represent approximately 30% of the overall number of BRCA1 mutation carriers that develop cancer in the US. We recently demonstrated that BRCA1 exon 11 mutation carriers had a significantly worse overall survival compared to patients with mutations outside of this exon, and outcomes were similar to the BRCA1 wild-type patient group. Cancers with exon 11-located mutations are capable of expressing the BRCA1-Δ11q alternative splice (AS) isoform that lacks the majority of exon 11, including stop codon-inducing mutations. Currently, little is known about the ability of BRCA1-Δ11q to repair DNA damage, maintain genome integrity, and induce chemo-resistance. In this project, we are assessing the role of BRCA1-Δ11q, and the splice factors that regulate its production, in DNA repair, tumor development and therapy sensitivity. Many BRCA1 mutation-carrying patients develop therapy resistance; new biological insights gained here may result in opportunities for the design of improved prevention or treatment strategies that optimally target BRCA1 mutant cancers.
This Fox Chase professor participates in the Undergraduate Summer Research Fellowship.
Learn more about Research Volunteering.
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