F2RL1

F2RL1 (PAR-2) is a proteinase-activated receptor that couples extracellular serine-protease cleavage to intracellular signaling cascades controlling tumor immune evasion, inflammation, and proliferation (PMID:41526166). In lung adenocarcinoma, extracellular granzyme K cleaves F2RL1 on tumor cells, activating AKT/GSK-3β/β-catenin and JAK2/STAT1 signaling; this drives nuclear accumulation of β-catenin and phosphorylated STAT1 to promote PD-L1 transcription, and additionally upregulates COPS8, which stabilizes PD-L1 by inhibiting its ubiquitin-mediated degradation, together suppressing CD8+ T-cell function (PMID:41526166). Beyond this immune-evasion axis, F2RL1 contributes to lipotoxic inflammatory injury in renal tubular epithelial cells and to glioma cell proliferation, but the downstream mechanisms in these contexts have not been resolved in the available corpus (PMID:39738821, PMID:38252207).

1. 2026 Medium

   Established that F2RL1 functions as a protease-activated signaling hub linking extracellular granzyme K to PD-L1-mediated tumor immune evasion, defining a mechanistic basis for combining protease inhibition with checkpoint blockade.

   Evidence Recombinant GZMK treatment in tumor-CD8+ T cell co-cultures, Western blot for AKT/GSK-3β/β-catenin and JAK2/STAT1, flow cytometry for PD-L1, and in vivo mouse models with GZMK inhibitor plus anti-PD-1

   PMID:41526166

   Open questions at the time

   • No reconstitution or structural validation of GZMK-mediated F2RL1 cleavage
   • Relative contributions of the β-catenin versus STAT1 arms to PD-L1 transcription not dissected
   • Mechanism by which F2RL1 signaling upregulates COPS8 unknown
2. 2024 Low

   Implicated F2RL1 in lipotoxicity-driven renal tubular inflammation, extending its role beyond cancer to diabetic kidney disease.

   Evidence siRNA knockdown of F2RL1 in palmitate-stimulated HK-2 cells with inflammatory factor readouts and DKD models

   PMID:39738821

   Open questions at the time

   • Hippo pathway placement is mechanistic inference, not demonstrated by epistasis or rescue
   • No identification of the activating protease in this context
   • No direct molecular link between F2RL1 and the measured inflammatory output
3. 2024 Low

   Showed F2RL1 supports glioma cell proliferation and is a target of melittin-mediated growth inhibition.

   Evidence Lentiviral F2RL1 knockdown plus melittin in U251 cells, proliferation/migration/invasion assays, cell-cycle and apoptosis flow cytometry, qRT-PCR, and xenografts

   PMID:38252207

   Open questions at the time

   • No direct molecular mechanism beyond F2RL1 expression level
   • No pathway placement for the proliferative effect
   • Whether melittin acts on F2RL1 directly is not established

• How F2RL1 signaling is differentially wired across cancer, renal, and glial contexts, and what physiological proteases activate it, remain open.
• No structural model of receptor activation or cleavage
• Endogenous activating proteases beyond GZMK not defined
• Context-specific downstream effectors (e.g., Hippo, cell-cycle genes) not mechanistically linked to F2RL1