| PTPN14 (tyrosine‑protein phosphatase non‑receptor type 14; Pez/PTPD2/PTP36) is a cytoplasmic non‑receptor protein tyrosine phosphatase of the band‑4.1/FERM‑domain subfamily that integrates cell–cell contact, cytoskeletal organization, and growth control through direct regulation of the Hippo effector YAP1 and adhesion‑associated substrates. The protein contains an N‑terminal FERM domain related to 4.1/ezrin/radixin/moesin that anchors PTPN14 to the plasma membrane and cortical actin networks, followed by extended low‑complexity linker regions harboring tandem PPXY (PY) motifs that mediate binding to WW‑domain proteins, and a C‑terminal classical PTP catalytic domain that defines it as a phosphatase but is dispensable for several of its key scaffolding functions. PTPN14 associates directly with YAP1 via its two PY motifs engaging both WW domains of YAP1, with the second WW domain contributing dominantly to this interaction; this binding relocates YAP1 from the nucleus to the cytoplasm under high cell density conditions, reduces YAP1 phosphorylation at Ser127 by upstream LATS kinases only indirectly, and suppresses YAP1 transcriptional coactivator activity toward proliferative and anti‑apoptotic targets such as CTGF and AREG, thereby enforcing contact inhibition and limiting acinar outgrowth in mammary epithelial 3D culture. The interaction with YAP1 and the ability to drive its nucleus‑to‑cytoplasm translocation depend on intact PY motifs and physical complex formation but do not require PTPN14 catalytic activity, as a Cys1121Ser phosphatase‑dead mutant retains full capacity to sequester YAP1 in the cytoplasm and to rescue aberrant acini formation caused by PTPN14 loss, whereas a PY‑motif–deleted mutant fails to bind YAP1, does not correct YAP1 nuclear accumulation, and cannot restore normal acinar architecture. PTPN14 levels and thus its restraining effect on YAP1 are controlled post‑translationally by cell density through the CRL2^LRR1^ E3 ubiquitin ligase complex: at low density, LRR1‑containing CRL2 binds PTPN14, promotes its polyubiquitylation and proteasomal degradation, and maintains low PTPN14 abundance with predominantly nuclear YAP1 and high proliferative potential; at confluence, LRR1 expression decreases, PTPN14 ubiquitination and turnover decline, PTPN14 accumulates, and YAP1 becomes retained in the cytoplasm in a manner that parallels but is mechanistically distinct from canonical Hippo kinase–14‑3‑3–dependent sequestration. PTPN14 also localizes to adherens junctions and cortical actin, where its FERM domain supports association with E‑cadherin/β‑catenin complexes, and in endothelial contexts, it mediates β‑catenin dephosphorylation at adhesion junctions, stabilizing E‑cadherin–β‑catenin linkage and contributing to barrier integrity and regulation of motility, while additional interactions with VEGFR3 and roles in lymphangiogenesis connect PTPN14 to vascular and lymphatic development. Loss of PTPN14 by shRNA in non‑transformed mammary epithelial cells drives anchorage‑independent growth, disrupts polarized acini with excessive proliferation and multiacinar structures, and these oncogenic phenotypes are reversed by concurrent YAP1 knockdown, placing YAP1 as a key downstream effector of PTPN14 tumor‑suppressive activity. |
Lane 1: ACHN, Lane 2: MDA-MB-231, Lane 3: HT-1080
