ITFG1

ITFG1 (LINKIN/LNKN-1) is a conserved transmembrane protein that couples cell–cell adhesion to microtubule dynamics during collective cell migration (PMID:25437307). Its extracellular region contains seven atypical FG-GAP domains predicted to fold into a β-propeller resembling the α-integrin ligand-binding domain, and it localizes to the plasma membrane to promote adhesion between neighboring cells (PMID:25437307). Through its intracellular domain it engages the AAA-ATPases RUVBL1 and RUVBL2 together with α-tubulin, linking adhesion to microtubule regulation (PMID:25437307, PMID:28341484). In breast cancer cells the RUVBL1–ITFG1 complex resides in the cytoplasm and at the plasma membrane and is required for collective invasion, as silencing either partner compromises invasion in vitro and in vivo (PMID:28341484). Additional interactors implicating membrane remodeling and chromosome biology in LINKIN-dependent tissue integrity have been identified (PMID:36798316), but beyond these interaction and adhesion-migration roles no further enzymatic or structural mechanism has been characterized in the available corpus.

1. 2014 High

   Established ITFG1/LINKIN as a transmembrane adhesion molecule whose extracellular FG-GAP domains mediate cell–cell adhesion while its intracellular domain controls microtubule dynamics, defining a single protein that bridges adhesion and the cytoskeleton.

   Evidence SILAC IP-MS interactome in HEK293T cells, C. elegans genetic loss-of-function, immunofluorescence localization, and domain analysis

   PMID:25437307

   Open questions at the time

   • β-propeller fold of the FG-GAP region is predicted, not structurally resolved
   • the adhesion ligand/binding partner on neighboring cells is not identified
   • no enzymatic activity assigned to ITFG1 itself
2. 2014 High

   Identified the intracellular binding partners (RUVBL1, RUVBL2, α-tubulin) that mechanistically connect ITFG1 to microtubule regulation, answering how a surface adhesion protein influences the cytoskeleton.

   Evidence SILAC co-IP-MS in HEK293T cells with C. elegans male gonad functional validation

   PMID:25437307 PMID:28341484

   Open questions at the time

   • the binding interface/domain on the ITFG1 cytoplasmic tail is not mapped
   • whether ITFG1 modulates RUVBL ATPase activity is unknown
   • stoichiometry of the ITFG1–RUVBL–tubulin assembly is undefined
3. 2017 High

   Showed the RUVBL1–ITFG1 interaction is functionally required for collective cancer cell invasion, extending the adhesion/microtubule role into a disease-relevant migratory program.

   Evidence Reciprocal Co-IP, immunofluorescence co-localization, siRNA knockdown, transwell and microfluidic invasion assays, xenograft and tail-vein mouse models in breast cancer cells

   PMID:28341484

   Open questions at the time

   • downstream effectors translating the complex into invasive behavior are not defined
   • single-lab finding
   • the contribution of the extracellular adhesion function versus intracellular RUVBL binding to invasion is not separated
4. 2023 Medium

   Broadened the LINKIN interactome to ATP9A, NME1, and ANAPC2, implicating membrane remodeling and chromosome biology in ITFG1-dependent adhesion through cross-species phenotype concordance.

   Evidence IP-MS in MDA-MB-231 cells, epitope-tag surface localization, and C. elegans loss-of-function of orthologs tat-5, ndk-1, apc-2 (preprint)

   PMID:36798316

   Open questions at the time

   • preprint, not yet peer-reviewed
   • direct physical versus indirect association of the new interactors not resolved
   • mechanistic link between membrane remodeling/chromosome biology and adhesion not established
5. 2012 Medium

   Mapped a translocation breakpoint within ITFG1 that silences a neighboring gene by position effect, characterizing the genomic context rather than ITFG1 protein function.

   Evidence FISH breakpoint mapping, real-time PCR expression analysis, chromatin immunoprecipitation, and pyrosequencing

   PMID:22475481

   Open questions at the time

   • phenotype attributed to position effect on NETO2/BTCL2, not to ITFG1 protein loss
   • no direct test of ITFG1 protein function
   • does not establish an ITFG1-intrinsic disease mechanism

• How ITFG1 transduces extracellular adhesion signals across the membrane to regulate RUVBL/tubulin-dependent microtubule dynamics, and what its true extracellular ligand is, remain unresolved.
• no structure of the FG-GAP β-propeller or the cytoplasmic interaction interface
• extracellular adhesion ligand unidentified
• no biochemical reconstitution of the ITFG1–RUVBL–tubulin assembly