Poly(ADP-ribose)polymerase-1 (PARP-1) is a highly promising novel target in breast cancer. However, the expression of PARP-1 protein in breast cancer and its associations with outcome are yet poorly characterized. Quantitative expression of PARP-1 protein was assayed by a specific immunohistochemical signal intensity scanning assay in a range of normal to malignant breast lesions, including a series of patients (N = 330) with operable breast cancer to correlate with clinicopathological factors and long-term outcome. PARP-1 was overexpressed in about a third of ductal carcinoma in situ and infiltrating breast carcinomas. PARP-1 protein overexpression was associated to higher tumor grade (P = 0.01), estrogen-negative tumors (P < 0.001) and triple-negative phenotype (P < 0.001). The hazard ratio (HR) for death in patients with PARP-1 overexpressing tumors was 7.24 (95% CI; 3.56–14.75). In a multivariate analysis, PARP-1 overexpression was an independent prognostic factor for both disease-free (HR 10.05; 95% CI 5.42–10.66) and overall survival (HR 1.82; 95% CI 1.32–2.52). Nuclear PARP-1 is overexpressed during the malignant transformation of the breast, particularly in triple-negative tumors, and independently predicts poor prognosis in operable invasive breast cancer.

Erythropoiesis is a tightly regulated process in which multipotential hematopoietic stem cells produce mature red blood cells. Here we show that deletion of poly(ADP-ribose) polymerase-2 (PARP-2) in mice leads to chronic anemia at steady state, despite increased erythropoietin plasma levels, a phenomenon not observed in mice lacking PARP-1. Loss of PARP-2 causes shortened lifespan of erythrocytes and impaired differentiation of erythroid progenitors. In erythroblasts, PARP-2 deficiency triggers replicative stress, as indicated by the presence of micronuclei, the accumulation of γ-H2AX (phospho-histone H2AX) in S-phase cells and constitutive CHK1 and replication protein A phosphorylation. Transcriptome analyses revealed the activation of the p53-dependent DNA-damage response pathways in PARP-2-deficient cells, culminating in the upregulation of cell-cycle and cell death regulators, concomitant with G2/M arrest and apoptosis. Strikingly, while loss of the proapoptotic p53 target gene Puma restored hematocrit levels in the PARP-2-deficient mice, loss of the cell-cycle regulator and CDK inhibitor p21 leads to perinatal death by exacerbating impaired fetal liver erythropoiesis in PARP-2-deficient embryos. Although the anemia displayed by PARP-2-deficient mice is compatible with life, mice die rapidly when exposed to stress-induced enhanced hemolysis. Our results pinpoint an essential role for PARP-2 in erythropoiesis by limiting replicative stress that becomes essential in the absence of p21 and in the context of enhanced hemolysis, highlighting the potential effect that might arise from the design and use of PARP inhibitors that specifically inactivate PARP proteins.

Key Points: Genetic inactivation of Parp-2 in mice, but not of Parp-1, resulted in bone marrow failure in response to sublethal γ-irradiation dose. Parp-2 plays an essential role in the DNA damage response in HSPC maintaining hematopoietic homeostasis under stress conditions.

The CD5 lymphocyte surface receptor is a group B member of the ancient and highly conserved scavenger receptor cysteine-rich superfamily. CD5 is expressed on mature T and B1a cells, where it is known to modulate lymphocyte activation and/or differentiation processes. Recently, the interaction of a few group B SRCR members (CD6, Spα, and DMBT1) with conserved microbial structures has been reported. Protein binding assays presented herein indicate that the CD5 ectodomain binds to and aggregates fungal cells (Schizosaccharomyces pombe,Candida albicans, andCryptococcus neoformans) but not to Gram-negative (Escherichia coli) or Gram-positive (Staphylococcus aureus) bacteria. Accordingly, the CD5 ectodomain binds to zymosan but not to purified bacterial cell wall constituents (LPS, lipotheicoic acid, or peptidoglycan), and such binding is specifically competed by β-glucan but not by mannan. TheK_dof the rshCD5/(1→3)-β-d-glucan phosphate interaction is 3.7 ± 0.2 nM as calculated from tryptophan fluorescence data analysis of free and bound rshCD5. Moreover, zymosan binds to membrane-bound CD5, and this induces both MAPK activation and cytokine release. In vivo validation of the fungal binding properties of the CD5 ectodomain is deduced from its protective effect in a mouse model of zymosan-induced septic shock-like syndrome. In conclusion, the present results indicate that the CD5 lymphocyte receptor may sense the presence of conserved fungal components [namely, (1→3)-β-d-glucans] and support the therapeutic potential of soluble CD5 forms in fungal sepsis.