PIN1 is the sole member of the peptidyl-prolyl cis-trans isomerase (PPIase) family, consisting of a WW domain and a catalytic domain, primarily localized to the nucleus and cytoplasm. It specifically recognizes and catalyzes the cis-trans isomerization of phosphorylated serine/threonine-proline peptide bonds, regulating the conformation and function of proteins. PIN1 plays a central role in cell cycle control, signal transduction, protein stability, and disease occurrence, influencing signaling pathways such as NF-κB and AP-1. Widely expressed in various tissues, overexpression or dysfunction of PIN1 is associated with diseases including cancer, Alzheimer's disease, and inflammatory responses. Studies on specific gene expression and mutations provide insight into its biological functions and disease associations.