The Yeast Pif1 Helicase Prevents Genomic Instability Caused by G-Quadruplex-Forming CEB1 Sequences In Vivo

In budding yeast, the Pif1 DNA helicase is involved in the maintenance of both nuclear and mitochondrial genomes, but its role in these processes is still poorly understood. Here, we provide evidence for a new Pif1 function by demonstrating that its absence promotes genetic instability of alleles of the G-rich human minisatellite CEB1 inserted in the Saccharomyces cerevisiae genome, but not of other tandem repeats. Inactivation of other DNA helicases, including Sgs1, had no effect on CEB1 stability. In vitro, we show that CEB1 repeats formed stable G-quadruplex (G4) secondary structures and the Pif1 protein unwinds these structures more efficiently than regular B-DNA. Finally, synthetic CEB1 arrays in which we mutated the potential G4-forming sequences were no longer destabilized in pif1Δ cells. Hence, we conclude that CEB1 instability in pif1Δ cells depends on the potential to form G-quadruplex structures, suggesting that Pif1 could play a role in the metabolism of G4-forming sequences

Role of BRAFV600E in the first preclinical model of multifocal infiltrating myopericytoma development and microenvironment

Myopericytoma (MPC) is a rare tumor with perivascular proliferation of pluripotent stem-cell-like pericytes. Although indolent, MPC may be locally aggressive with recurrent disease. The pathogenesis and diagnostic biomarkers of MPC are poorly understood. We discovered that 15% of benign MPCs (thyroid, skin; 3 of 20 samples) harbored BRAF(WT/V600E); 33.3% (1 of 3 samples) of BRAF(WT/V600E)-MPCs were multifocal/infiltrative/recurrent. Patient-MPC and primary MPC cells harbored BRAF(WT/V600E), were clonal and expressed pericytic-differentiation biomarkers crucial for its microenvironment. BRAF(WT/V600E)-positive thyroid MPC primary cells triggered in vitro (8.8-fold increase) and in vivo (3.6-fold increase) angiogenesis. Anti-BRAF(V600E) therapy with vemurafenib disrupted angiogenic and metabolic properties (~3-fold decrease) with down-regulation (~2.2-fold decrease) of some extracellular-matrix (ECM) factors and ECM-associated long non-coding RNA (LincRNA) expression, with no effects in BRAF(WT)-pericytes. Vemurafenib also inhibited (~3-fold decrease) cell viability in vitro and in BRAF(WT/V600E)-positive thyroid MPC patient-derived xenograft (PDX) mice (n = 5 mice per group). We established the first BRAF(WT/V600E)-dependent thyroid MPC cell culture. Our findings identify BRAF(WT/V600E) as a novel genetic aberration in MPC pathogenesis and MPC-associated biomarkers and imply that anti-BRAF(V600E) agents may be useful adjuvant therapy in BRAF(WT/V600E)-MPC patients. Patients with BRAF(WT/V600E)-MPC should be closely followed because of the risk for multifocality/recurrence

Autoantibody against transient receptor potential M1 cation channels of retinal ON bipolar cells in paraneoplastic vitelliform retinopathy

<p>Abstract</p> <p>Background</p> <p>Paraneoplastic retinopathy is caused by the cross-reaction of neoplasm-directed autoantibodies against retinal antigens and results in retinal damage. Paraneoplastic vitelliform retinopathy, a presumed paraneoplastic retinopathy with features of atypical melanoma-associated retinopathy, has recently been reported in patients with metastatic melanoma. Ocular ultrastructure and its autoantibody localization of paraneoplastic vitelliform retinopathy are still indefinable. This is the first report of anti-transient receptor potential M1 antibody directly against human retinal bipolar dendritic tips in a melanoma patient with paraneoplastic vitelliform retinopathy.</p> <p>Case presentation</p> <p>We present a pair of postmortem eyes of an 80-year-old male with metastatic cutaneous melanoma, who developed paraneoplastic vitelliform retinopathy. The autopsied eyes were examined with light microscopy, immunohistochemistry, and transmission electron microscopy. Microscopically, the inner nuclear layer and outer plexiform layer were the most affected retinal structures, with local thinning. The lesions extended to the outer nuclear layer, resulting in focal retinal degeneration, edema, and atrophy. No active inflammation or melanoma cells were observed. Immunohistochemistry showed tightly compact bipolar cell nuclei (protein kinase C alpha/calbindin positive) with blur/loss of ON bipolar cell dendritic tips (transient receptor potential M1 positive) in diffusely condensed outer plexiform layer. The metastatic melanoma cells in his lung also showed immunoreactivity against transient receptor potential M1 antibody. Transmission electron microscopy illustrated degenerated inner nuclear layer with disintegration of cells and loss of cytoplasmic organelles. These cells contained many lysosomal and autophagous bodies and damaged mitochondria. Their nuclei appeared pyknotic and fragmentary. The synapses in the outer plexiform layer were extensively degenerated and replaced with empty vacuoles and disintegrated organelles.</p> <p>Conclusion</p> <p>This case provides a convincing histological evidence of melanoma-associated autoantibodies directly against transient receptor potential M1 channels that target the ON bipolar cell structures in the inner nuclear and outer plexiform layers in paraneoplastic vitelliform retinopathy.</p