PTPRA

PTPRA (RPTPα) is a receptor-type protein tyrosine phosphatase that controls tyrosine kinase signaling output in opposing ways depending on substrate context (PMID:32062451, PMID:35900966). It binds the RET receptor tyrosine kinase and directly dephosphorylates it, with its membrane-proximal first phosphatase domain (domain-1) being indispensable for suppressing RET activity and downstream Ras-MAPK signaling; PTPRA restrains the oncogenic MEN2A RET mutant and its invasion phenotype, whereas the MEN2B mutant is insensitive to it (PMID:32062451). In contrast to its inhibitory action on RET, PTPRA positively drives Src family kinase activation, and the p.R223W missense mutation that alters RPTPα proteolytic processing leads to decreased Src family kinase activation (PMID:35900966). This PTPRA-SRC axis is held in check by miR-146a-5p, which binds the PTPRA 3'-UTR to repress its expression; loss of this repression elevates phospho-SRC and promotes a fibrotic phenotype in hepatic stellate cells and irradiated liver (PMID:31560641, PMID:38014555). Beyond these signaling roles, no broader cellular or structural mechanism for PTPRA has been characterized in the available corpus.

1. 1995 Low

   Before functional studies, the genomic position of Ptpra was unknown; mapping placed the gene on rat chromosome 3q36 and mouse chromosome 2G, establishing conserved synteny with human 20p13 and a basis for cross-species study.

   Evidence Fluorescence in situ hybridization in rat and mouse

   PMID:8790445

   Open questions at the time

   • Single mapping study with no functional mechanism established
   • No link to protein activity or substrates
2. 2019 Medium

   It was unclear how PTPRA expression is post-transcriptionally controlled and what kinase it regulates; miR-146a-5p was shown to bind the PTPRA 3'-UTR to repress it, defining a PTPRA-SRC signaling axis whose loss promotes fibrotic markers in hepatic stellate cells.

   Evidence Dual-luciferase 3'-UTR reporter, western blot for SRC phosphorylation, and miR-146a-5p overexpression with PTPRA rescue in LX2 cells

   PMID:31560641

   Open questions at the time

   • Whether PTPRA dephosphorylates an inhibitory SRC site directly was not biochemically reconstituted
   • Single-lab in vitro evidence
3. 2020 High

   The direct substrate of PTPRA in receptor tyrosine kinase signaling was undefined; interactome and dephosphorylation assays identified RET as a direct substrate and showed domain-1 is required for suppressing RET-driven Ras-MAPK signaling and invasion, with differential effects on MEN2A versus MEN2B mutants.

   Evidence Phosphatome interactome mapping, co-IP, in vivo and in vitro dephosphorylation assays, domain deletion/mutagenesis, invasion assays

   PMID:32062451

   Open questions at the time

   • Why the MEN2B mutant is insensitive to PTPRA is not mechanistically explained
   • Cell-type breadth of the PTPRA-RET relationship not established
4. 2020 Low

   Whether PTPRA influences inflammatory transcription was untested; reporter and cell-based assays indicated PTPRA promotes TNF-α-mediated NF-κB activity, proliferation, and migration in MCF-7 breast cancer cells.

   Evidence NF-κB luciferase reporter in HEK293T, growth/colony/Transwell assays with PTPRA knockdown and overexpression in MCF-7 cells

   PMID:32934700

   Open questions at the time

   • No biochemical reconstitution of how PTPRA connects to NF-κB
   • Single-lab cell-based evidence only
   • Direct phosphatase substrate in this pathway not identified
5. 2022 Medium

   The consequence of the PTPRA p.R223W variant was unknown; comparison of WT and mutant protein showed normal expression and membrane trafficking but altered proteolytic processing and decreased Src family kinase activation, linking proteolytic processing to RPTPα signaling output.

   Evidence WT vs R223W overexpression in HEK293T, western blot for cleavage products, membrane trafficking assay, Src family kinase activation assay

   PMID:35900966

   Open questions at the time

   • The protease responsible for the altered cleavage is not identified
   • Physiological/disease context of R223W not established in patients
   • Single-lab cellular system
6. 2023 Medium

   It was unclear whether the miR-146a-5p/PTPRA-SRC axis operates in vivo; agomir treatment of irradiated mice reduced PTPRA and phospho-SRC in liver, confirming the axis in radiation-induced liver fibrosis.

   Evidence Fractionated liver irradiation mouse model with miR-146a-5p agomir, western blot for PTPRA and phospho-SRC, histopathology

   PMID:38014555

   Open questions at the time

   • Direct demonstration that PTPRA acts on SRC enzymatically in this tissue is lacking
   • Other miR-146a-5p targets could contribute to the phenotype

• How PTPRA reconciles its opposing roles — inhibiting RET while activating Src family kinases — and what governs substrate selection, localization, and proteolytic regulation across tissues remains unresolved.
• No structural model linking domain-1/domain-2 architecture to substrate choice
• Mechanism coupling proteolytic processing to SFK activation undefined
• Physiological regulators of PTPRA expression beyond miR-146a-5p unknown