# Homeostatic Regulation of PIP2-Calcium Signaling

> **NIH NIH R01** · UT SOUTHWESTERN MEDICAL CENTER · 2024 · $388,341

## Abstract

PROJECT SUMMARY / ABSTRACT
 Phosphatidylinositol 4,5-bisphosphate (PIP2)-Ca2+ signaling is activated following stimulation of growth
factor receptors, antigen receptors, and G protein-coupled receptors by ligands including neurotransmitters and
histamine. The activation of phospholipase C triggers hydrolysis of the PIP2 lipid at the plasma membrane (PM)
to generate diacylglycerol (DAG) and inositol trisphosphate (IP3). IP3 subsequently releases Ca2+ stored in the
endoplasmic reticulum (ER) to activate cytosolic Ca2+ effectors for downstream signaling events such as
secretion, proliferation, and migration. The consumed PM PIP2 and ER Ca2+ must be quickly restored to sustain
signaling responses and to maintain cellular homeostasis. This homeostatic regulation of PIP2-Ca2+ signaling
requires transport of phosphatidylinositol (PI) from the ER to the PM for PIP2 resynthesis and store-operated
Ca2+ entry (SOCE) that activates Ca2+ influx to refill the ER Ca2+ store. SOCE has been studied extensively;
however, the mechanisms underlying PIP2 replenishment during PIP2-Ca2+ signaling are not well understood.
Recently, we and others discovered the lipid transfer protein Nir2 that localizes at ER-PM junctions, where the
ER is in contact with the PM, to mediate PM PIP2 replenishment. The objective of this proposal is to define the
mechanisms regulating PIP2 replenishment by Nir2 at ER-PM junctions during receptor-induced Ca2+ signaling.
Our preliminary studies identified Nir1, an Nir protein lacking a lipid transfer protein domain, as a binding partner
and positive regulator of Nir2 at ER-PM junctions. In addition, our recent data revealed that the membrane-
shaping hairpin sequence present in all extended synaptotagmins (E-Syts) is important for regulating PIP2
replenishment at ER-PM junctions. Moreover, we found that conversion of DAG into phosphatidic acid (PA) by
DAG kinases (DGKs) is crucial for Nir2 localization at ER-PM junctions. Among the ten DGKs in mammalian
cells, the epsilon-isoform of DGK (DGKε) is recently shown to localize at ER-PM junctions. Our central hypothesis
is that PM PIP2 replenishment during receptor-induced Ca2+ signaling is mediated by the oligomers of Nir1 and
Nir2 formed following PA production from DAG by DGKε at ER-PM junctions shaped by E-Syts. We propose
three specific aims to test our central hypothesis using biochemical analysis and advanced imaging techniques
to determine the mechanisms by which Nir1, E-Syts and DGKε regulate PIP2 replenishment. We expect that
successfully completion of the proposed studies will establish the molecular and cellular mechanisms regulating
PIP2 replenishment following hydrolysis induced by receptor stimulation. Restoring PM PIP2 is critical to sustain
Ca2+ signaling and maintain PM PIP2 levels critical to membrane trafficking, cytoskeletal dynamics, and ion
transport in receptor-stimulated cells. Mutations in Nir1 are linked to retinal dystrophy and patients with mutations
in DGKε suffer from...

## Key facts

- **NIH application ID:** 10824365
- **Project number:** 5R01GM144479-03
- **Recipient organization:** UT SOUTHWESTERN MEDICAL CENTER
- **Principal Investigator:** JEN LIOU
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $388,341
- **Award type:** 5
- **Project period:** 2022-07-15 → 2026-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10824365

## Citation

> US National Institutes of Health, RePORTER application 10824365, Homeostatic Regulation of PIP2-Calcium Signaling (5R01GM144479-03). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/10824365. Licensed CC0.

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