Endosomal Trafficking Bypassed by the RAB5B‐CD109 Interplay Promotes Axonogenesis in <i>KRAS</i>‐Mutant Pancreatic Cancer

Perineural invasion (PNI) represents a unique biological feature associated with poor prognosis in pancreatic ductal adenocarcinoma (PDAC), especially in the presence of KRAS mutations. Extracellular vesicle (EV)-packaged circular RNAs (circRNAs) function as essential mediators of tumor microenvironment communication, triggering PDAC cell invasion and distant metastasis. However, the regulatory mechanisms of EV-packaged circRNAs in the PNI of KRAS-mutant PDAC have not yet been elucidated. Herein, a KRAS^G12D mutation-responsive EV-packaged circRNA, circPNIT, which positively correlated with PNI in PDAC patients is identified. Functionally, KRAS^G12D PDAC-derived EV-packaged circPNIT promoted axonogenesis and PNI both in vitro and in vivo. Mechanistically, the circPNIT-mediated Rab5B-CD109 interplay bypassed traditional endosomal trafficking to anchor Rab5B to the lipid rafts of multivesicular bodies and packaged circPNIT into CD109⁺ EVs. Subsequently, CD109⁺ EVs delivered circPNIT to neurons by binding to TRPV1 and facilitating DSCAML1 transcription-induced axonogenesis, which in turn enhanced the PNI by activating the GFRα1/RET pathway. Importantly, circPNIT-loaded CD109⁺ EVs are established to dramatically promote PNI in a KRAS^G12D/+ Trp53^R172H/+ Pdx-1-Cre mouse model. Collectively, the findings highlight the mechanism underlying how EV-packaged circRNAs mediate the PNI of KRAS-mutant PDAC cells through the Rab5B endosomal bypass, identifying circPNIT as an effective target for the treatment of neuro-metastatic PDAC.