SPRED3

SPRED3 is a negative regulator of Ras/MAPK signaling that suppresses growth factor-induced ERK activation through its C-terminal cysteine-rich SPR domain, which also mediates membrane localization and a non-canonical interaction with the palmitoyl acyltransferase zDHHC17 for S-acylation (PMID:12646235, PMID:36442513). Unlike SPRED1/2, SPRED3 lacks a functional c-Kit binding domain due to a critical Arg-to-Gly substitution, and it does not interact with RSK2, indicating paralog-specific regulatory wiring within the SPRED family (PMID:12646235, PMID:37149146). Loss of SPRED3 activates Ras/Raf/MAPK signaling to drive EGFR-TKI resistance in NSCLC and causes primary hypothyroidism with dysregulated thyroidal ERK signaling and autophagy in knockout mice (PMID:35117614, PMID:40806788). SPRED3 also modulates NF-κB signaling in thyroid cancer cells and blocks TGFβ-induced EMT and FGF-driven differentiation in lens epithelial cells (PMID:39227612, PMID:25576668, PMID:29501879).

1. 2003 High

   Establishing that SPRED3 suppresses growth factor-induced ERK activation resolved how this third family member functions and revealed that its SPR domain, rather than its non-functional KBD, drives both membrane targeting and ERK suppression — distinguishing it mechanistically from SPRED1/2.

   Evidence Domain-swap chimeras and deletion mutants with ERK activation assays in overexpression system

   PMID:12646235

   Open questions at the time

   • Endogenous SPRED3 loss-of-function not tested
   • SPR domain binding partners mediating membrane localization unidentified
   • No in vivo validation
2. 2006 Medium

   Demonstrating that SPRED3 is ubiquitinated upon growth factor stimulation established that proteasomal degradation regulates SPRED3 protein levels, paralleling the regulatory mechanism of SPRED1/2.

   Evidence Co-immunoprecipitation/ubiquitination assays in HEK293T cells with EGF stimulation and MG-132 treatment

   PMID:17094949

   Open questions at the time

   • E3 ubiquitin ligase responsible not identified
   • Ubiquitination sites on SPRED3 not mapped
   • Functional consequence of ubiquitination on ERK suppression not tested
3. 2014 Medium

   Identification of zDHHC17 (HIP14) as the palmitoyl acyltransferase that S-acylates SPRED3 provided the first enzyme-substrate link for SPRED3 lipid modification, suggesting a regulatory mechanism for its membrane association.

   Evidence Yeast two-hybrid screen for HIP14 interactors followed by palmitoylation assays

   PMID:24705354

   Open questions at the time

   • Functional consequence of palmitoylation on SPRED3 ERK suppression not tested
   • Palmitoylation sites not mapped
   • Mechanism of enzyme-substrate recognition unclear
4. 2015 Medium

   Showing that SPRED3 blocks TGFβ-induced EMT in lens epithelial cells extended its inhibitory role beyond classical RTK-ERK signaling to TGFβ-driven cellular reprogramming.

   Evidence SPRED3 overexpression in rat lens epithelial explants with TGFβ treatment; morphological and α-SMA marker assessment

   PMID:25576668

   Open questions at the time

   • Whether SPRED3 directly inhibits TGFβ pathway components or acts via ERK cross-talk unclear
   • Endogenous SPRED3 expression in lens tissue not confirmed
   • Mechanism of EMT suppression not defined
5. 2018 Medium

   Demonstration that SPRED3 blocks FGF-induced lens fiber differentiation by suppressing ERK1/2 phosphorylation confirmed its role as a general negative regulator of RTK-MAPK signaling in a developmental context.

   Evidence SPRED3 transfection in lens explants with FGF stimulation; p-ERK1/2 and Prox1 marker readouts

   PMID:29501879

   Open questions at the time

   • Endogenous SPRED3 function in lens development not tested by knockout
   • Relative contribution of SPRED3 vs SPRED1/2 in lens tissue unknown
6. 2020 High

   Discovery that loss-of-function SPRED3 mutations activate Ras/Raf/MAPK signaling and confer EGFR-TKI resistance in NSCLC established SPRED3 as a clinically relevant tumor suppressor, with reciprocal knockout and overexpression validating causality.

   Evidence Whole-exome sequencing of erlotinib-resistant cells; CRISPR knockout and cDNA rescue; p-ERK, MTS, and migration assays

   PMID:35117614

   Open questions at the time

   • Frequency of SPRED3 loss in clinical EGFR-TKI resistance cohorts unknown
   • Direct interaction partner at the Raf level not defined
   • Whether SPRED3 loss cooperates with other resistance mechanisms untested
7. 2021 High

   Identifying miR-342-5p as a direct negative regulator of SPRED3 via 3′UTR targeting linked SPRED3 downregulation to neonatal lung pathology, revealing a post-transcriptional regulatory axis controlling SPRED3 abundance in vivo.

   Evidence 3′UTR luciferase reporter assay; miR-342-5p gain/loss in murine BPD models; recombinant Spred3 treatment

   PMID:33434946

   Open questions at the time

   • Paradoxical worsening with recombinant Spred3 in BPD model not mechanistically explained
   • Whether Spred3 engages Raf1 directly or indirectly not resolved
8. 2022 High

   Defining that zDHHC17 S-acylates SPRED3 through an ANK-independent, SPR domain-mediated mechanism revealed a non-canonical mode of enzyme-substrate recognition distinct from other zDHHC17 substrates.

   Evidence Mutational analysis of SPRED3 and zDHHC17 ANK-deletion mutants; co-immunoprecipitation and S-acylation assays

   PMID:36442513

   Open questions at the time

   • Specific cysteine residues acylated not mapped
   • Whether S-acylation is required for SPRED3 membrane targeting and ERK suppression in cells not tested
   • Structural basis of SPR-zDHHC17 recognition unknown
9. 2023 Medium

   AP-MS interactome comparison showing RSK2 binds SPRED2 but not SPRED3 established that SPRED paralogs occupy distinct signaling niches despite shared domain architecture.

   Evidence Affinity purification mass spectrometry of SPRED1/2/3 interactomes

   PMID:37149146

   Open questions at the time

   • SPRED3-specific interactors not comprehensively characterized
   • Functional consequence of differential RSK2 binding on MAPK feedback not tested
10. 2024 Medium

    Discovery that SPRED3 activates NF-κB transcriptional activity and promotes thyroid cancer cell proliferation uncovered a signaling role beyond MAPK inhibition, supported by reciprocal gain/loss-of-function and in vivo xenograft data.

    Evidence Flag-SPRED3 overexpression and CRISPR knockout in thyroid cancer cells; NF-κB luciferase reporter; mouse xenograft

    PMID:39227612

    Open questions at the time

    • Mechanism by which SPRED3 activates NF-κB not defined
    • Reconciliation of tumor-suppressive MAPK role with tumor-promoting NF-κB role not addressed
    • Whether NF-κB activation is direct or indirect unknown
11. 2025 High

    SPRED3 knockout mice developing primary hypothyroidism with reduced thyroidal ERK signaling and dysregulated autophagy established the first in vivo physiological function for SPRED3, linking it to thyroid hormone homeostasis.

    Evidence Constitutive SPRED3 KO mouse; serum TSH/T4 profiling; immunoblotting for ERK, p62, ATG5, LC3, Beclin; X-Gal promoter activity mapping

    PMID:40806788

    Open questions at the time

    • Whether hypothyroidism results from direct thyroidal SPRED3 loss or secondary hypothalamic-pituitary effects not fully resolved
    • How a MAPK inhibitor's loss leads to mildly reduced (not increased) thyroidal ERK requires mechanistic explanation
    • Autophagy dysregulation could be secondary to hormonal changes

• The structural basis of SPRED3's SPR domain-mediated inhibition of Raf, the identity of SPRED3-specific protein interaction partners, and the mechanistic reconciliation of its MAPK-suppressive versus NF-κB-activating roles remain unresolved.
• No crystal or cryo-EM structure of SPRED3 or SPR domain in complex with Raf or zDHHC17
• SPRED3-specific interactome incompletely defined
• Context-dependent tumor-suppressive vs oncogenic functions not mechanistically explained