# Probing adenylate kinase-dependent CFTR gating in vivo and as therapeutic target

> **NIH NIH R01** · UNIVERSITY OF IOWA · 2020 · $381,250

## Abstract

Loss of function of the ATP-binding cassette (ABC) transporter cystic fibrosis transmembrane conductance
regulator (CFTR), a Cl- and HCO3- channel, causes cystic fibrosis (CF). CF lung and intestinal disease are the
most consequential disease manifestations. The most common mutation, deletion of phenylalanine 508
(F508del), disrupts CFTR processing and reduces the rate of channel opening. Increased CFTR activity
underlies water and electrolyte losses in cholera toxin-induced diarrhea. For both diseases there is a need for
better treatments that normalize CFTR channel function. CFTR and other ABC proteins have both ATPase and
adenylate kinase activity. The traditional paradigm of CFTR function has been that opening and closing
("gating") of the channel is coupled to ATPase activity. It is not known whether adenylate kinase activity
contributes to CFTR function in vivo, and whether this activity is a meaningful target to treat CFTR-related
diseases. In preliminary studies we made two pertinent discoveries. 1) We identified a CFTR mutation
(Q1291F) that abolished adenylate kinase activity but had no significant effect on ATPase-dependent gating. It
reduced Cl- channel activity in primary human airway epithelia. 2) We found that the adenylate kinase inhibitor
Ap5A (P1,P5-di(adenosine-5') pentaphosphate) - in striking contrast to wild-type CFTR - increased channel
activity of F508del CFTR. The objective of this application is to build on these preliminary data to ascertain a
contribution of adenylate kinase-dependent CFTR gating in vivo and to provide a proof-of-concept that a
compound interacting with the adenylate kinase active center might be a clinically useful potentiator of F508del
CFTR. The central hypothesis is that normal CFTR function in disease-relevant organs, airways and intestine,
relies on its adenylate kinase activity and that - as a consequence of a structural defect - Ap5A potentiates
F508del CFTR channel activity through interactions with residue Q1291. In aim 1 we will use primary airway
epithelia and examine the effects of Q1291F CFTR on HCO3- secretion and airway surface liquid (ASL) pH,
which both play a pivotal role in the development of CF lung disease. We will also investigate whether 1)
expression of Q1291F CFTR rescues the intestinal phenotype of CFTR-/- mice and 2) the mutation reduces
cholera toxin-induced intestinal fluid losses. In aim 2 we will investigate how Ap5A interacts with F508del CFTR
to potentiate channel activity using biochemical and electrophysiological approaches. These studies are
expected to lead to new treatment approaches for CF and CFTR-dependent diarrheas. The proposed research
is innovative because it addresses an understudied mechanism of CFTR gating, adenylate kinase activity, and
seeks to shift the current paradigm of how CFTR functions in vivo. Furthermore, it builds on the unanticipated
discovery that Ap5A potentiates F508del CFTR channel activity. Furthermore, the proposed research is
relevant...

## Key facts

- **NIH application ID:** 10004609
- **Project number:** 5R01DK107489-04
- **Recipient organization:** UNIVERSITY OF IOWA
- **Principal Investigator:** Christoph Oskar Randak
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $381,250
- **Award type:** 5
- **Project period:** 2017-08-03 → 2023-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10004609

## Citation

> US National Institutes of Health, RePORTER application 10004609, Probing adenylate kinase-dependent CFTR gating in vivo and as therapeutic target (5R01DK107489-04). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/10004609. Licensed CC0.

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