Prolactin Induced Protein (PIP)

The hormonally responsive prolactin-inducible protein gene is expressed in benign and malignant breast tumor tissues and in some normal exocrine organs such as sweat, salivary, and lacrimal glands.The PIP gene is 7 kb long with 4 exons ranging from 106 bp to 223 bp.

PIP is overexpressed in 80% of primary and metastatic breast cancers, is duplicated in the breast carcinoma cell line T47D. The 2 copies are organized as a large palindrome, lying 'in loco' on one chromosome 7. The FRA7I fragile site lies 2 Mb telomeric to the PIP gene and sets the distal end of the repeated sequence. Breakage at the FRA7I site was repaired by 1 cycle of the breakage--fusion-bridge (BFB) cycle mechanism, resulting in amplification of the PIP gene.