Poly(ADP-ribose) polymerase-1 in breast cancers: expression level and its association in various molecular subtypes...

Poly(ADP-ribose) polymerases (PARPs) are important nuclear protein enzymes (NPEs) that play crucial functions in different cellular activities including DNA repair, gene transcription, post-translational, and cell death. Of the 17 established PARP family members, PARP-1 is a NPE with 113-116 kDa which is encoded by a gene found on chromosome 1q41-q42-1, and is the most abundant enzyme, with approximately 1-2 million molecules per cell, acting principally as a DNA damage sensor. PARP-1 has become an auspicious biological novel target for management of various cancers. Increased expression of PARP-1 has been documented in various types of malignancies such as melanomas, lung cancers, and breast cancers (BCs), and is associated with disease progression and reduced survival outcome. Expression of PARP-1 has been valuable as a prognostic factor in patients with BC especially triple negative phenotype and also human epidermal receptor-2 enriched compared to luminal subtypes. The prognostic role of PARP-1 in BCs is based on the use of PARP-1 inhibitors such as olaparib and talazoparib which usually inhibit the cancer cells from undergoing repair through homologous recombination repair (HRR) and base excision repair (BER), hence leading to their death. This review dissects the level of expression of PARP-1 and its association in different immunohistochemically determined molecular subtypes of BC.