# Updating the toolbox: applying CRISPR towards the study of the xenobiotic transporter MDR1

> **NIH NIH R03** · SCRIPPS FLORIDA · 2020 · $88,625

## Abstract

Project Summary
Multidrug resistance (MDR)-1 is a plasma membrane-associated, ATP-dependent efflux pump widely
recognized—and named—for removing chemotherapeutic compounds from drug-resistant tumor cells.
Whereas endogenous substrates and functions of MDR1 have remained enigmatic for nearly 50 years, both
the presence of MDR1 orthologs in prokaryotes and an emerging body of literature suggest that MDR1 has
broader and more fundamental functions in cell biology beyond simply interfacing with synthetic medicines.
Using CRISPR/Cas9-mediated genome editing in mouse zygotes, we previously created a fluorescent MDR1
reporter mouse (Abcb1aAME/+) and showed that MDR1 is expressed in a variety of lymphocyte lineages at
steady-state. We have gone on to show two examples of how endogenous MDR1 functions serve to support
the establishment and maintenance of lymphocyte homeostasis in vivo. First, we have shown that MDR1 acts
intrinsically in CD4+ T helper (TH) cells infiltrating the small intestinal mucosa to enforce homeostasis, limit
pathogenic cytokine expression and suppress Crohn’s disease-like ileitis in the presence of naturally-
circulating bile acids. More recently, we have found that MDR1 is constitutively expressed in cytolytic
lymphocytes, including CD8+ cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells, due to direct
regulation by runt-related (Runx) transcription factors. In CTLs, MDR1 promotes the survival of cytolytic
effector cells, such that loss or pharmacologic inhibition of MDR1 leads to increased CTL death, reduced
expression of key cytolytic effector molecules (e.g., perforin, granzyme B), impaired CTL-dependent target cell
killing in vitro, and diminished CTL-dependent anti-tumor immunity in vivo. As a whole, these innovative
preliminary studies highlight diverse and important functions of MDR1 in normal immune physiology. Our long-
term objectives are to elucidate additional cellular contexts where endogenous MDR1 functions regulate
physiologic immune responses, whilst defining core classes of endogenous MDR1 transport substrates in vivo.
Because existing genetic tools (e.g., RNAi, whole-body MDR1 knockout mice) are not sufficient to address
these question, we will leverage our collective expertise in CRISPR/Cas9-based genome editing to generate
the first conditional MDR1 (Abcb1a) knockout mouse. Successful generation of these mice will pave the way
for myriad future studies utilizing conditional gene ablation to explore the diverse molecular functions of MDR1
in immune, parenchymal and malignant cells.

## Key facts

- **NIH application ID:** 9965740
- **Project number:** 5R03AI144714-02
- **Recipient organization:** SCRIPPS FLORIDA
- **Principal Investigator:** Sergei Borisovich Koralov
- **Activity code:** R03 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $88,625
- **Award type:** 5
- **Project period:** 2019-07-01 → 2021-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9965740

## Citation

> US National Institutes of Health, RePORTER application 9965740, Updating the toolbox: applying CRISPR towards the study of the xenobiotic transporter MDR1 (5R03AI144714-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9965740. Licensed CC0.

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