# Functional architecture of intracellular Ca2+ signals

> **NIH NIH R01** · MEDICAL COLLEGE OF WISCONSIN · 2024 · $448,715

## Abstract

PROJECT SUMMARY
Increases in cellular Ca2+ resulting from activation of intracellular Ca2+ channels regulate many physiological
events. Dysfunction of intracellular Ca2+ signaling pathways is involved in many disease states. To appreciate
how cell functions are controlled by Ca2+ signals, and how pathological cues subvert their function, we must
understand how the `functional architecture' of intracellular ion channels controls Ca2+ signaling dynamics.
In this proposal, we investigate the mechanistic basis of Ca2+ release mediated by the second messenger
nicotinic acid adenine dinucleotide phosphate (NAADP). NAADP potently releases Ca2+ from endosomes and
lysosomes by activating a family of cation channels called two-pore channels (TPCs). These signals locally
regulate trafficking of endolysosomal cargoes and can be amplified into whole cell Ca2+ signals by Ca2+-
induced Ca2+ release through neighboring Ca2+ channels on the endoplasmic reticulum (ER). However, the
molecular basis of NAADP-evoked Ca2+ release is unclear as no NAADP binding site has been identified on
the TPC protein. Rather NAADP acts via an unidentified NAADP binding protein (NAADP-BP) associated with
the TPC complex to mediate TPC activation. Here, a multi-PI team (Marchant, Patel, Slama): (i) designed a
novel bifunctional probe to enable a photolabeling strategy that has identified the elusive NAADP-BP as Jupiter
Microtubule Associated Homolog 2 (JPT-2), and (ii) optimized novel TPC activatory ligands that mimic NAADP
action. These tools provide opportunity to finally decipher the molecular basis of NAADP action. This proposal
coalesces medicinal chemistry, molecular analyses, and high-resolution imaging expertise to resolve:
 (1) How NAADP binds to JPT2, and how JPT2 associates with TPCs. We will define the nucleotide
 binding characteristics of JPT2, and the role of JPT2 in conferring NAADP sensitivity to TPCs
 (2) The functional impact of JPT2 on NAADP-evoked Ca2+ signals. We will probe the essentiality and cell
 biology of JPT2, resolving its role in endogenous NAADP-evoked Ca2+ signals and targeting of TPCs to
 specialized microdomains (membrane contact sites) that couple to endoplasmic reticulum Ca2+ channels.
(3) How NAADP sensitivity is regulated physiologically. Identification of JPT2 provides a molecular
 handle to investigate how cellular NAADP sensitivity is physiologically controlled by regulation of JPT2
 stability. We show JPT2 and TPCs interact with tankyrase, a poly-ADP-ribosyltransferase. We
 hypothesize that JPT2 is a tankyrase substrate, with cellular JPT2 levels controlled by ADP ribosylation.

## Key facts

- **NIH application ID:** 10734042
- **Project number:** 5R01GM088790-16
- **Recipient organization:** MEDICAL COLLEGE OF WISCONSIN
- **Principal Investigator:** JONATHAN S MARCHANT
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $448,715
- **Award type:** 5
- **Project period:** 2004-07-01 → 2025-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10734042

## Citation

> US National Institutes of Health, RePORTER application 10734042, Functional architecture of intracellular Ca2+ signals (5R01GM088790-16). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10734042. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*