PRR4 (proline-rich 4) is a protein synthesized in acinar cells of lacrimal and salivary glands with multifaceted roles in ocular and systemic biology. As a component of tear and salivary proteomes, PRR4 exhibits antimicrobial properties that protect the ocular surface and oral cavity 1. The protein undergoes complex post-translational modifications including methylation, acetylation, oxidation, and pyroglutamate formation, generating multiple isoforms with molecular weights of 17-30 kDa in tears 2. In healthy salivary glands, a specific PRR4+CST3+WFDC2- seromucous acinar cell population exists that is selectively lost in Sjögren's disease due to targeting by GZMK+CD8+ T cells, contributing to exocrine gland dysfunction 34. PRR4 serves as a biomarker for ocular surface disorders, with expression detected in dry eye disease and ocular allergy contexts 5. In laryngeal cancer, PRR4 expression is significantly reduced in tumor tissues (72.2% of cases), suggesting a protective role against carcinogenesis 1. Additionally, circRNA PRH1-PRR4 functions as a competing endogenous RNA regulating non-small-cell lung cancer progression via the miR-877-5p/RAB3D pathway 6. PRR4 methylation patterns show sex-specific age-dependent changes 7, indicating epigenetic regulation relevant to aging and longevity.