Microcystins are toxins produced by cyanobacteria that entail serious health and environmental problems. They are cyclic heptapeptides synthesized via a mixed polyketide synthase/non-ribosomal peptide synthetase system called microcystin synthetase. Environmental and nutritional factors that trigger microcystin synthesis are still debated and this work deals with the study of the influence of iron nutritional status on the microcystin synthesis. The results indicate that iron deficiency could be one of the inducing factors of the microcystin synthesis. For the first time, increased transcription of an essential mcy gene and correlative microcystin synthesis has been established. Real-time PCR analysis of mcyD, and microcystin-LR synthesis were studied on Microcystis aeruginosa PCC7806 grown in iron-replete and iron-deplete media. Iron starvation causes an increase of mcyD transcription, correlative to the increase of microcystin-LR levels. Four transcription start points were identified for mcyD and two for mcyA, and they are not changed as a consequence of iron deficiency.

BackgroundChronic lymphocytic leukemia (CLL), the most common adulthood leukemia, is characterized by the accumulation of abnormal CD5+ B lymphocytes, which results in a progressive failure of the immune system. Despite intense research efforts, drug resistance remains a major cause of treatment failure in CLL, particularly in patients with dysfunctional TP53. The objective of our work was to identify potential approaches that might overcome CLL drug refractoriness by examining the pro-apoptotic potential of targeting the cell surface receptor CD47 with serum-stable agonist peptides.Methods and FindingsIn peripheral blood samples collected from 80 patients with CLL with positive and adverse prognostic features, we performed in vitro genetic and molecular analyses that demonstrate that the targeting of CD47 with peptides derived from the C-terminal domain of thrombospondin-1 efficiently kills the malignant CLL B cells, including those from high-risk individuals with a dysfunctional TP53 gene, while sparing the normal T and B lymphocytes from the CLL patients. Further studies reveal that the differential response of normal B lymphocytes, collected from 20 healthy donors, and leukemic B cells to CD47 peptide targeting results from the sustained activation in CLL B cells of phospholipase C gamma-1 (PLCγ1), a protein that is significantly over-expressed in CLL. Once phosphorylated at tyrosine 783, PLCγ1 enables a Ca2+-mediated, caspase-independent programmed cell death (PCD) pathway that is not down-modulated by the lymphocyte microenvironment. Accordingly, down-regulation of PLCγ1 or pharmacological inhibition of PLCγ1 phosphorylation abolishes CD47-mediated killing. Additionally, in a CLL-xenograft model developed in NOD/scid gamma mice, we demonstrate that the injection of CD47 agonist peptides reduces tumor burden without inducing anemia or toxicity in blood, liver, or kidney. The limitations of our study are mainly linked to the affinity of the peptides targeting CD47, which might be improved to reach the standard requirements in drug development, and the lack of a CLL animal model that fully mimics the human disease.ConclusionsOur work provides substantial progress in (i) the development of serum-stable CD47 agonist peptides that are highly effective at inducing PCD in CLL, (ii) the understanding of the molecular events regulating a novel PCD pathway that overcomes CLL apoptotic avoidance, (iii) the identification of PLCγ1 as an over-expressed protein in CLL B cells, and (iv) the description of a novel peptide-based strategy against CLL.