Atg4 proteolytic activity can be inhibited by Atg1 phosphorylation.

The biogenesis of autophagosomes depends on the conjugation of Atg8-like proteins with phosphatidylethanolamine. Atg8 processing by the cysteine protease Atg4 is required for its covalent linkage to phosphatidylethanolamine, but it is also necessary for Atg8 deconjugation from this lipid to release it from membranes. How these two cleavage steps are coordinated is unknown. Here we show that phosphorylation by Atg1 inhibits Atg4 function, an event that appears to exclusively occur at the site of autophagosome biogenesis. These results are consistent with a model where the Atg8-phosphatidylethanolamine pool essential for autophagosome formation is protected at least in part by Atg4 phosphorylation by Atg1 while newly synthesized cytoplasmic Atg8 remains susceptible to constitutive Atg4 processing.The protease Atg4 mediates Atg8 lipidation, required for autophagosome biogenesis, but also triggers Atg8 release from the membranes, however is unclear how these steps are coordinated. Here the authors show that phosphorylation by Atg1 inhibits Atg4 at autophagosome formation sites.

Myelodysplastic cells in patients reprogram mesenchymal stromal cells to establish a transplantable stem cell niche disease unit.

Myelodysplastic syndromes (MDSs) are a heterogeneous group of myeloid neoplasms with defects in hematopoietic stem and progenitor cells (HSPCs) and possibly the HSPC niche. Here, we show that patient-derived mesenchymal stromal cells (MDS MSCs) display a disturbed differentiation program and are essential for the propagation of MDS-initiating Lin(-)CD34(+)CD38(-) stem cells in orthotopic xenografts. Overproduction of niche factors such as CDH2 (N-Cadherin), IGFBP2, VEGFA, and LIF is associated with the ability of MDS MSCs to enhance MDS expansion. These factors represent putative therapeutic targets in order to disrupt critical hematopoietic-stromal interactions in MDS. Finally, healthy MSCs adopt MDS MSC-like molecular features when exposed to hematopoietic MDS cells, indicative of an instructive remodeling of the microenvironment. Therefore, this patient-derived xenograft model provides functional and molecular evidence that MDS is a complex disease that involves both the hematopoietic and stromal compartments. The resulting deregulated expression of niche factors may well also be a feature of other hematopoietic malignancies.

Improvement of replication fidelity by certain mesalazine derivatives.

Epidemiological evidence on the chemopreventive activity of mesalazine against colitis-associated cancer has accumulated in recent years. Together with the variety of mesalazine molecular antitumor effects this has prompted the development of novel mesalazine derivatives. The objective of this study was to test five novel derivatives (compounds 2-14, 2-17, 2-28, 2-34L, 2-39) for their effect on cell proliferation, their capability to scavenge superoxide anions, to induce a cell cycle arrest and to improve replication fidelity in cultured colorectal cells. Compound 2-14 was identified as the strongest inhibitor of cell proliferation and functioned as a potent superoxide scavenger, as did 2-17 and 2-34L. 2-14 induced a G2/M-arrest in HCT116 and a G0/G1-arrest in HT29 cells. 2-17 caused a G0/G1-arrest and 2-34L a G2/M-arrest in HT29 cells. 2-17 and 2-34L reduced mutation rates at a (CA)13 repeat in a dose-dependent fashion. These data suggest that certain mesalazine derivatives share important antitumor effects. From this experimental profile compounds 2-17 and 2-34L both improve replication fidelity, which is biologically relevant not only for colitis-associated cancer but also potentially for individuals with hereditary non-polyposis colorectal cancer.