title: PPM1D gene amplification and overexpression in breast cancer: a qRT-PCR and chromogenic in situ hybridization study.
abstract: PPM1D (protein phosphatase magnesium-dependent 1δ) maps to the 17q23.2 amplicon and is amplified in ∼8% of breast cancers. The PPM1D gene encodes a serine threonine phosphatase, which is involved in the regulation of several tumour suppressor pathways, including the p53 pathway. Along with others, we have recently shown that PPM1D is one of the drivers of the 17q23.2 amplicon and a promising therapeutic target. Here we investigate whether PPM1D is overexpressed when amplified in breast cancers and the correlations between PPM1D overexpression and amplification with clinicopathological features and survival of breast cancer patients from a cohort of 245 patients with invasive breast cancer treated with therapeutic surgery followed by adjuvant anthracycline-based chemotherapy. mRNA was extracted from representative sections of tumours containing >50% of tumour cells and subjected to TaqMan quantitative real-time PCR using primers for PPM1D and for two housekeeping genes. PPM1D overexpression was defined as the top quartile of expression levels. Chromogenic in situ hybridization with in-house-generated probes for PPM1D was performed. Amplification was defined as >50% of cancer cells with >5 signals per nucleus/large gene clusters. PPM1D overexpression and amplification were found in 25 and 6% of breast cancers, respectively. All cases harbouring PPM1D amplification displayed PPM1D overexpression. PPM1D overexpression was inversely correlated with expression of TOP2A, EGFR and cytokeratins 5/6 and 17. PPM1D amplification was significantly associated with HER2 overexpression, and HER2, TOP2A and CCND1 amplification. No association between PPM1D gene amplification and PPM1D mRNA overexpression with survival was observed. In conclusion, PPM1D is consistently overexpressed when amplified; however, PPM1D overexpression is more pervasive than gene amplification. PPM1D overexpression and amplification are associated with tumours displaying luminal or HER2 phenotypes. Co-amplification of PPM1D and HER2/TOP2A and CCND1 are not random events and may suggest the presence of a 'firestorm' genetic profile.
authors.affiliation: The Breakthrough Breast Cancer Research Centre, Institute of Cancer Research, London, UK.
authors.forename: Maryou B
authors.initials: MB
authors.lastname: Lambros
authors.forename: Rachael
authors.initials: R
authors.lastname: Natrajan
authors.forename: Felipe C
authors.initials: FC
authors.lastname: Geyer
authors.forename: Maria A
authors.initials: MA
authors.lastname: Lopez-Garcia
authors.forename: Konstantin J
authors.initials: KJ
authors.lastname: Dedes
authors.forename: Kay
authors.initials: K
authors.lastname: Savage
authors.forename: Magali
authors.initials: M
authors.lastname: Lacroix-Triki
authors.forename: Robin L
authors.initials: RL
authors.lastname: Jones
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Lord
authors.forename: Spiros
authors.initials: S
authors.lastname: Linardopoulos
authors.forename: Alan
authors.initials: A
authors.lastname: Ashworth
authors.forename: Jorge S
authors.initials: JS
authors.lastname: Reis-Filho
mesh_terms: D001943:Breast Neoplasms / Q000235:genetics* / Q000401:mortality / Q000473:pathology*; D005260:Female; D005784:Gene Amplification; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D053208:Kaplan-Meier Estimate; D010749:Phosphoprotein Phosphatases / Q000235:genetics*; D011379:Prognosis; D000071636:Protein Phosphatase 2C; D020133:Reverse Transcriptase Polymerase Chain Reaction; D046888:Tissue Array Analysis
chemical_list: C000607458:PPM1D protein, human; D010749:Phosphoprotein Phosphatases; D000071636:Protein Phosphatase 2C