Secreted protein that acts as a key regulator of lysosomal function and as a growth factor involved in inflammation, wound healing and cell proliferation (By similarity). Regulates protein trafficking to lysosomes and, also the activity of lysosomal enzymes (By similarity). Facilitates also the acidification of lysosomes, causing degradation of mature CTSD by CTSB (By similarity). In addition, functions as wound-related growth factor that acts directly on dermal fibroblasts and endothelial cells to promote division, migration and the formation of capillary-like tubule structures (By similarity). Also promotes epithelial cell proliferation by blocking TNF-mediated neutrophil activation preventing release of oxidants and proteases (By similarity). Moreover, modulates inflammation in neurons by preserving neurons survival, axonal outgrowth and neuronal integrity (By similarity). Inhibits epithelial cell proliferation and induces epithelial cells to secrete IL-8. Stabilizes CTSD through interaction with CTSD leading to maintain its aspartic-type peptidase activity. Progranulin is secreted as a homodimer. Interacts with SLPI; interaction protects progranulin from proteolysis. Interacts (via region corresponding to granulin-7 peptide) with CTSD; stabilizes CTSD and increases its proteolytic activity. Interacts (via region corresponding to granulin-7 peptide) with SORT1; this interaction mediates endocytosis and lysosome delivery of progranulin; interaction occurs at the neuronal cell surface in a stressed nervous system. Interacts with PSAP; facilitates lysosomal delivery of progranulin from the extracellular space and the biosynthetic pathway. Forms a complex with PSAP and M6PR; PSAP bridges the binding between progranulin and M6PR. Forms a complex with PSAP and SORT1; progranulin bridges the interaction between PSAP and SORT1; facilitates lysosomal targeting of PSAP via SORT1; interaction enhances PSAP uptake in primary cortical neurons. Interacts (via regions corresponding to granulin-2 and granulin-7 peptides) with GBA; this interaction prevents aggregation of GBA-SCARB2 complex via interaction with HSPA1A upon stress. Interacts (via region corresponding to granulin-7 peptide) with HSPA1A; mediates recruitment of HSPA1A to GBA and prevents GBA aggregation in response to stress. Endocytosed by SORT1 and delivred to lysosomes. Targeted to lysosome by PSAP via M6PR and LRP1, in both biosynthetic and endocytic pathways (By similarity). Co-localized with GBA in the intracellular trafficking compartments until to lysosome (By similarity). Ubiquitous; most abundant in the spleen and several tissues of endocrine significance. Cleaved by ELANE; proteolysis is blocked by SLPI and is concentration- and time-dependent and induces CXCL8/IL-8 production; granulin-3 and granulin-4 are resistant to ELANE. Cleaved by CTSL in lysosome thus regulating the maturation and turnover of progranulin within the lysosome. Belongs to the granulin family.