CTTNBP2NL

CTTNBP2NL is a cortactin-binding protein that associates with stress fibers and functions as a scaffolding component of striatin-PP2A signaling, distinguishing it functionally from its paralog CTTNBP2 in that it does not regulate dendritic spinogenesis (PMID:23015759). It binds cortactin and assembles with the PP2A regulatory B subunits striatin (STRN) and zinedin, placing CTTNBP2NL within a striatin-PP2A complex (PMID:23015759). Consistent with a role in directing phosphatase activity, CTTNBP2NL mediates dephosphorylation of the gap junction protein connexin 43, and its overexpression inhibits embryo implantation in mice (PMID:24218568). Beyond these activities, the broader mechanistic logic linking its cortactin/stress-fiber association, striatin-PP2A scaffolding, and connexin 43 dephosphorylation has not been integrated in the available corpus.

1. 2011 Low

   Establishing whether CTTNBP2NL is a bona fide striatin-associated protein anchored the gene to the striatin interaction network and gave it a candidate scaffolding context.

   Evidence Experimental Co-IP/pull-down validation of an IP-MS-predicted CTTNBP2NL-STRN interaction

   PMID:22219718

   Open questions at the time

   • Single experimental validation from a pan-proteomics study, single method
   • Stoichiometry and direct versus indirect nature of the STRN interaction not resolved
   • Functional consequence of the interaction not tested
2. 2012 Medium

   Defining CTTNBP2NL's partners and localization separated it from its paralog CTTNBP2, showing it binds cortactin and decorates stress fibers without driving dendritic spinogenesis.

   Evidence Reciprocal Co-IP, subcellular localization in neurons and HEK293 cells, and spine-morphology functional readout

   PMID:23015759

   Open questions at the time

   • Mechanism by which CTTNBP2NL is targeted to stress fibers rather than cortical actin is unknown
   • The functional output of cortactin binding for CTTNBP2NL is not defined
   • No structural basis for partner selection established
3. 2012 Low

   Co-IP of CTTNBP2NL with striatin and zinedin placed it in a striatin-PP2A complex, providing a candidate route to phosphatase-directed signaling.

   Evidence Co-immunoprecipitation in HEK293 cells

   PMID:23015759

   Open questions at the time

   • Single Co-IP in heterologous cells, single method
   • Whether CTTNBP2NL recruits or modulates PP2A catalytic activity not shown
   • Substrate targeting by the complex not addressed
4. 2013 Medium

   Demonstrating CTTNBP2NL-dependent dephosphorylation of connexin 43 linked the protein to gap junction regulation and provided an in vivo phenotype.

   Evidence Biochemical connexin 43 dephosphorylation assay plus a mouse embryo implantation model with CTTNBP2NL overexpression

   PMID:24218568

   Open questions at the time

   • Whether dephosphorylation is direct or via the associated PP2A complex is not resolved
   • Connexin 43 residues targeted not mapped
   • Mechanistic link between connexin 43 status and implantation failure unclear
5. 2025 Low

   Identifying TEAD1 as an upstream regulator of CTTNBP2NL expression connected the gene to a transcriptional control axis affecting tumor cell survival.

   Evidence qPCR, Western blot, and overexpression/knockdown in TPC1 papillary thyroid carcinoma cells with proliferation, apoptosis, and colony formation assays

   PMID:41216228

   Open questions at the time

   • Indirect transcriptional relationship without a direct promoter-binding assay
   • Single cell line and single lab
   • Mechanistic role of CTTNBP2NL downstream of TEAD1 not defined
6. 2026 Low

   Reporting CTTNBP2NL as a nuclear/nucleolar negative regulator of autophagy whose cytoplasmic translocation activates autophagy proposed a new localization-dependent function.

   Evidence Peptidomics, cellular fractionation, Tat-HSPE1 interaction assay, and autophagy activation readout in ccRCC cells

   PMID:42147335

   Open questions at the time

   • Indirect evidence via peptide interaction with limited mechanistic detail
   • How nuclear CTTNBP2NL suppresses autophagy is not defined
   • Relationship between this nuclear role and its cytoplasmic stress-fiber/striatin functions unknown

• It remains unknown how CTTNBP2NL's cortactin/stress-fiber association, striatin-PP2A scaffolding, connexin 43 dephosphorylation, and reported nuclear autophagy regulation are mechanistically unified.
• No structural model of CTTNBP2NL or its complexes
• Direct catalytic versus adaptor contribution to dephosphorylation unresolved
• Whether nuclear and cytoskeletal functions reflect distinct pools or a single regulated mechanism is untested