PLEKHA6

PLEKHA6 is a PH- and WW-domain-containing scaffold protein that organizes membrane trafficking and cell-junction signaling in epithelial cells (PMID:34613798, PMID:34568338). Through its WW domains it binds the N-terminus of PDZD11, and this PLEKHA6–PDZD11 complex is required for efficient anterograde delivery of the Menkes copper ATPase ATP7A to the cell periphery under elevated copper, thereby promoting copper extrusion and maintaining cellular copper homeostasis (PMID:34613798). Its subcellular positioning is set cooperatively by distinct regions: the C-terminal region directs localization to adherens junctions, while the WW-mediated PDZD11 interaction supports cytoplasmic microtubule association (PMID:34568338). In cancer contexts PLEKHA6 acts as a positive regulator of Wnt/β-catenin signaling, with its loss suppressing β-catenin and VE-cadherin expression and impairing proliferation, migration, and survival of lung adenocarcinoma cells (PMID:40814363). Oncogenic chromosomal rearrangements fusing PLEKHA6 to NTRK3 generate a chimeric protein that activates the RAS-RAF-MEK-ERK pathway and drives cell growth (PMID:30098202).

1. 2000 Low

   The first question was whether PLEKHA6 (PEPP3) could engage membrane phosphoinositides through its PH domain, which would define it as a lipid-binding module.

   Evidence In vitro phosphoinositide-binding assay of expressed PH domains and EST-based motif search, with PEPP3 binding inferred from homology to PEPP1/PEPP2

   PMID:11001876

   Open questions at the time

   • PtdIns3P binding was inferred from homology, not directly demonstrated for PEPP3/PLEKHA6
   • no cellular function attached to the lipid-binding activity
   • no structural characterization of the PH domain
2. 2018 Medium

   A clinical genomics finding addressed whether PLEKHA6 rearrangements have oncogenic potential, establishing that a PLEKHA6-NTRK3 fusion drives mitogenic signaling.

   Evidence Whole-genome sequencing to identify the fusion plus overexpression of the PLEKHA6-NTRK3 construct in NIH 3T3 cells with MAPK activation and growth assays

   PMID:30098202

   Open questions at the time

   • tested only by overexpression in NIH 3T3, not in patient-derived contexts
   • contribution of the PLEKHA6 portion versus NTRK3 kinase to transformation not dissected
   • does not address endogenous PLEKHA6 function
3. 2021 High

   The core mechanistic question of what PLEKHA6 does was answered by showing its WW domains bind PDZD11 to promote anterograde trafficking of ATP7A and control copper homeostasis.

   Evidence Reciprocal pull-downs, CRISPR-KO of PLEKHA5/6/7 in kidney epithelial cells, immunofluorescence of ATP7A, and copper/metallothionein/viability readouts

   PMID:34613798

   Open questions at the time

   • redundancy among PLEKHA5/6/7 not fully resolved
   • molecular mechanism linking the complex to the trafficking machinery not defined
   • in vivo relevance to organismal copper handling untested
4. 2021 Medium

   A parallel study addressed how PLEKHA6 is targeted within cells, showing its localization is partitioned between adherens junctions and microtubules by separable domains.

   Evidence Domain-deletion and chimeric WW-PLEKHA constructs expressed in cultured cells with immunofluorescence

   PMID:34568338

   Open questions at the time

   • based on ectopic constructs rather than endogenous protein
   • junctional and microtubule pools not linked to specific functional outputs
   • single-lab imaging readout
5. 2025 Medium

   Whether PLEKHA6 influences a defined signaling pathway in cancer was tested, placing it as a positive regulator of Wnt/β-catenin signaling in lung adenocarcinoma.

   Evidence siRNA/shRNA knockdown in A549 cells with Western blot for β-catenin/VE-cadherin and proliferation, migration, colony, apoptosis, and cell-cycle assays

   PMID:40814363

   Open questions at the time

   • mechanism linking PLEKHA6 to β-catenin stability or transcription not defined
   • single cell line, single lab
   • relationship between this signaling role and its ATP7A/PDZD11 trafficking function unknown

• It remains unknown how PLEKHA6's scaffolding/trafficking activity mechanistically connects to its reported roles in Wnt/β-catenin signaling and how these are integrated within polarized epithelia.
• no unifying mechanism linking copper-ATPase trafficking, junctional localization, and β-catenin regulation
• no in vivo or structural data on the full-length protein
• endogenous regulation and upstream signals unknown