PIP (prolactin induced protein) is a 17-kDa secreted glycoprotein with diverse regulatory functions across multiple tissues 1. The protein exhibits aspartic-type endopeptidase activity, specifically degrading fibronectin, which contributes to its role in cell migration and invasion 1. PIP serves as a critical regulator of aquaporin 5 (AQP5) trafficking in salivary and lacrimal glands, where it interacts with the AQP5 C-terminus to control proper apical membrane localization 2. In corneal tissue, PIP accelerates wound healing by promoting epithelial cell and fibroblast migration while exhibiting anti-fibrotic properties through downregulation of TGF-β1, smooth muscle actin, and collagen III 3. In breast cancer, PIP is widely expressed and regulated by androgen and prolactin signaling through STAT5, Runx2, and CREB1 transcription factors 1. The protein is essential for integrin-β1 outside-in signaling activation and promotes cell proliferation and invasion in breast cancer cells 1. PIP dysfunction is associated with Sjögren's syndrome, where altered PIP expression correlates with abnormal AQP5 localization and salivary gland hypofunction 2. These findings establish PIP as a multifunctional protein important for tissue homeostasis, wound repair, and disease pathogenesis.