PACSIN3

PACSIN3 is a membrane-active F-BAR/SH3 scaffold protein that couples its membrane-tubulating and phosphoinositide-binding activities to the regulation of plasma membrane channels, receptors, and trafficking compartments (PMID:19997509, PMID:23690576). Through its SH3 domain it engages proline-rich cytoplasmic regions of partner proteins: it binds the N-terminal proline-rich region of the TRPV4 channel as a class I polyproline II helix and rigidifies the adjacent PIP2 binding site, an interaction that, together with the F-BAR domain, restricts PIP2 access and inhibits TRPV4 activation by cell swelling and heat (PMID:23690576, PMID:30244966). By an analogous SH3–proline-rich contact it binds the ADAM12 cytoplasmic tail and up-regulates ADAM12-mediated proHB-EGF ectodomain shedding (PMID:12952982). PACSIN3 also directs membrane trafficking: it promotes GLUT1 plasma membrane localization to increase glucose uptake in adipocytes (PMID:17320047) and positions the mechanosensitive Piezo1 channel at the intercellular bridge to control Rab11-FIP3 endosome and ESCRT-III delivery during cytokinetic abscission (PMID:34714681). Its scaffolding role requires an intact membrane-inserting EFC/F-BAR prong and high-affinity phosphoinositide binding, which are needed for axial mesoderm cell polarization and notochord formation in zebrafish (PMID:19997509).

1. 2003 High

   Established PACSIN3 as a cytoplasmic adaptor for the metalloprotease ADAM12 and a positive regulator of ectodomain shedding, defining its first molecular partner and functional output.

   Evidence Yeast two-hybrid, GST pull-down, reciprocal Co-IP, co-localization, and overexpression/siRNA shedding assays mapping binding to ADAM12 residues 829-840

   PMID:12952982

   Open questions at the time

   • Did not resolve which PACSIN3 domain mediates ADAM12 binding
   • Mechanism by which PACSIN3 enhances shedding (trafficking vs. activation) not defined
2. 2007 Medium

   Extended PACSIN3 function to glucose transporter trafficking, showing it selectively routes GLUT1 to the plasma membrane.

   Evidence Overexpression in 3T3-L1 adipocytes with subcellular fractionation, photoaffinity labeling, and glucose uptake assays

   PMID:17320047

   Open questions at the time

   • Direct physical interaction with GLUT1 not demonstrated
   • Single lab, overexpression-based; loss-of-function effect untested
   • No GLUT4 effect, leaving the basis for cargo selectivity unexplained
3. 2007 Low

   Identified PACSIN3 in a FasL interactome in Schwann cells, hinting at a broader role in surface receptor trafficking in the nervous system.

   Evidence Proteomics/co-immunoprecipitation screen

   PMID:17761170

   Open questions at the time

   • Single proteomics screen with no PACSIN3-specific functional follow-up
   • Direct binding and physiological relevance unconfirmed
4. 2009 High

   Defined the structural requirements for PACSIN3's membrane-active scaffolding in vivo, linking EFC/F-BAR membrane insertion and phosphoinositide binding to morphogenetic cell migration.

   Evidence Morpholino knockdown in zebrafish with cross-species rescue by Drosophila Syndapin EFC mutants and biochemical phosphoinositide binding assays

   PMID:19997509

   Open questions at the time

   • Molecular cargo or partners driving notochord cell migration not identified
   • Endocytic step coupled to migration not directly visualized
5. 2013 High

   Revealed PACSIN3 as a negative regulator of TRPV4, showing it inhibits mechanical and thermal channel activation in an F-BAR-dependent manner by limiting PIP2 access.

   Evidence Heterologous co-expression, FRET of TRPV4 tail proximity, F-BAR deletion constructs, and electrophysiology

   PMID:23690576

   Open questions at the time

   • How the F-BAR domain mechanically restricts PIP2 access was not structurally resolved
   • Physiological context of TRPV4 inhibition in tissue not addressed
6. 2018 High

   Provided atomic-resolution mechanism for the PACSIN3–TRPV4 interaction and established a hierarchical SH3/PIP2 binding network at the TRPV4 N-terminus.

   Evidence NMR structure of PACSIN3 SH3–TRPV4 PRR complex with ITC/NMR affinity measurements and mutagenesis

   PMID:30244966

   Open questions at the time

   • Full-length channel/PACSIN3 architecture not determined
   • Functional consequence of the cis-proline conformational switch on gating not tested directly
7. 2019 Low

   Implicated cytokine signaling in controlling PACSIN3 abundance, showing IL-6 represses PACSIN3 protein post-transcriptionally during myoblast differentiation.

   Evidence miRNA microarray, qRT-PCR, and Western blot in IL-6- or IGF-I-treated primary rat skeletal myoblasts

   PMID:31820147

   Open questions at the time

   • No direct demonstration that miR-154-3p/miR-338-3p repress PACSIN3 mRNA
   • Functional consequence of PACSIN3 loss in myogenesis not tested here
8. 2021 Medium

   Placed PACSIN3 upstream of Piezo1-dependent endosome trafficking in cytokinesis, connecting it to the membrane scission machinery of abscission.

   Evidence Genetic knockdown with live-cell imaging of the intercellular bridge, immunolocalization of Piezo1/Rab11-FIP3/ALIX/ESCRT-III, and multinucleation readout

   PMID:34714681

   Open questions at the time

   • Direct PACSIN3–Piezo1 interaction not biochemically demonstrated
   • Single lab; mechanism of endosome mispositioning not resolved at molecular detail

• Whether the diverse PACSIN3 functions (channel regulation, cargo trafficking, caveolar biogenesis, cytokinesis) reflect one unified membrane-remodeling activity or distinct context-specific roles remains unresolved.
• No unified structural/functional model linking F-BAR membrane tubulation to its various cargo outputs
• Endogenous tissue-specific partner inventory incomplete
• Direct disease-causing mutations not defined in primary data