PIP Gene (Prolactin-Induced Protein): Function, Expression, and Disease Associations

The PIP gene encodes a secreted protein known as prolactin-induced protein (PIP) or gross cystic disease fluid protein 15 (GCDFP-15). It is expressed in various exocrine tissues, including salivary, lacrimal, and sweat glands, as well as in the breast. PIP is involved in immune modulation, cell growth, and differentiation. It is a well-established marker for breast cancer, particularly for apocrine differentiation, and is also associated with other cancers and autoimmune conditions.

Tissue Expression

Cell Line Expression

Hotspot Mutations

Mutation functional classification

• Prolactin signaling pathway (Reactome: R-HSA-1433557)

• Androgen receptor signaling pathway (Reactome: R-HSA-5625740)

The prolactin-induced protein (PIP) is a 146-amino-acid secreted glycoprotein with a molecular weight of approximately 16.5 kDa. It is synthesized as a precursor with a signal peptide and is processed to the mature form. PIP functions as an aspartyl protease inhibitor and is involved in immune modulation, including inhibition of T-cell apoptosis and regulation of cytokine production. It is highly expressed in apocrine glands and is a classic marker for apocrine differentiation in breast pathology. The protein is also implicated in the pathogenesis of Sjögren's syndrome as an autoantigen.