LRIG3 evidence notes

Identity and architecture

LRIG3 is a type-I single-pass membrane member of the LRIG family. Its extracellular
LRR/Ig architecture supports receptor association but does not make LRIG3 an autonomous
signaling receptor. The two reviewed UniProt isoforms differ in sequence, but no source
GO annotation is isoform-qualified and the reviewed literature does not establish an
isoform-specific function.

Receptor regulation

The strongest human evidence shows that "Lrig3 opposes Lrig1 negative regulatory"
activity and stabilizes ERBB receptors PMID:23723069. Vertebrate experiments also
show that "Lrig3, like Lrig1, is able" to associate with ERBB receptors in vitro, while
ERBB inhibition did not reproduce the Lrig3-dependent inner-ear phenotype
PMID:20126551. Thus receptor-regulator activity is supported, but LRIG1's degradation
mechanism must not be transferred wholesale to LRIG3.

Developmental evidence

Mouse genetics establishes that "Lrig3 is necessary" for lateral semicircular-canal
development through cross-repression with Ntn1 PMID:19004851. Xenopus work concludes
that "Lrig3 functions in NC formation in Xenopus" through context-dependent WNT/FGF
modulation PMID:18287203. These are important developmental contexts, not direct
evidence for human hearing perception or a single shared receptor mechanism.

Glioma and soluble LRIG3

Human glioma-cell studies report that "LRIG3 by shRNA resulted in significantly increase"
of invasion/adhesion and growth PMID:19200647. Later work confirms the "existence of
soluble ectodomain of LRIG3" in culture supernatant and patient fluids and links both
full-length and soluble protein to MET-PI3K-AKT-associated tumor suppression
PMID:31245283. LRIG3 also "significantly suppressed glioma-induced angiogenesis"
through PI3K-AKT/VEGFA-associated effects PMID:33718179. In the tumor microenvironment,
"sLRIG3 interacts with the CUB1 domain of NETO2" in macrophages and limits M2-like
polarization in the tested models PMID:36639372. These results define strong
context-specific cancer biology but do not establish the normal physiological role,
the endogenous shedding protease, or a universal soluble-LRIG3 pathway.

Evidence boundaries

• Tear-fluid proteomics supports only detection in "tear fluid from breast carcinoma patients"
  PMID:22664934; it does not distinguish intact protein, shed ectodomain,
  vesicle-associated material, or cellular debris.
• The BioPlex observation comes from "mass spectrometry, we have created two proteome-scale"
  networks PMID:33961781 and is corroborative screen evidence, not proof of an
  obligate LRIG1-LRIG3 complex.
• LRIG1 and LRIG2 receptor mechanisms, mouse auditory phenotypes, Xenopus neural-crest
  biology, and glioma-derived soluble-LRIG3 effects remain separately bounded.