Oncogene-induced DNA replication stress has been implicated as a driver of tumorigenesis. Many chromosomal rearrangements characteristic of human cancers originate from specific regions of the genome called common fragile sites (CFSs). CFSs are difficult-to-replicate loci that manifest as gaps or breaks on metaphase chromosomes (termed CFS 'expression'), particularly when cells have been exposed to replicative stress. The MUS81-EME1 structure-specific endonuclease promotes the appearance of chromosome gaps or breaks at CFSs following replicative stress. Here we show that entry of cells into mitotic prophase triggers the recruitment of MUS81 to CFSs. The nuclease activity of MUS81 then promotes POLD3-dependent DNA synthesis at CFSs, which serves to minimize chromosome mis-segregation and non-disjunction. We propose that the attempted condensation of incompletely duplicated loci in early mitosis serves as the trigger for completion of DNA replication at CFS loci in human cells. Given that this POLD3-dependent mitotic DNA synthesis is enhanced in aneuploid cancer cells that exhibit intrinsically high levels of chromosomal instability (CIN(+)) and replicative stress, we suggest that targeting this pathway could represent a new therapeutic approach.

Most of the targeting moieties, such as antibody fragments or growth factor domains, used to construct targeted toxins for anticancer therapy derive from secretory proteins. These normally fold in the oxidative environment of the endoplasmic reticulum, and hence their folding in bacterial cells can be quite inefficient. For instance, only low amounts of properly folded antimetastatic chimera constituted by the amino-terminal fragment of human urokinase (ATF) fused to the plant ribosome-inactivating protein saporin could be recovered. ATF-saporin was instead secreted efficiently when expressed in eukaryotic cells protected from autointoxication with neutralizing anti-saporin antibodies. Pichia pastoris is a microbial eukaryotic host where these domains can fold into a transport-competent conformation and reach the extracellular medium. We show here that despite some host toxicity codon-usage optimization greatly increased the expression levels of active saporin but not those of an active-site mutant SAP-KQ in GS115 (his4) strain. The lack of any toxicity associated with expression of the latter confirmed that toxicity is due to saporin catalytic activity. Nevertheless, GS115 (his4) cells in flask culture secreted 3.5 mg/L of a histidine-tagged ATF-saporin chimera showing an IC(50) of 6 x 10(-11) M against U937 cells, thus demonstrating the suitability of this expression platform for secretion of toxic saporin-based chimeras.

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Surgical removal is the mainstay for early lung cancer treatment and persistent air leaks represent one of the most common clinical complications after lung surgery. Adipose tissue transplantation has been proposed as a new strategy for regenerative therapy after breast cancer surgery; however its efficacy and safety of lung tissue healing after lung resections are unknown. The purpose of this study was to test the biological activity of adipose tissue to facilitate lung tissue healing and evaluate its effect on cancer cells growth, thus providing insight for a possible clinical application. Different in vitro cellular models were used to prove the potential biologic effect of autologous fat tissue (AFT) in repairing injured lung tissue, and in vivo xenograft models were used to evaluate tumor promoting potential of AFT on putative residual cancer cells. Treatment of both embryonic (WI-38) and adult lung fibroblasts and of normal bronchial epithelial cells (HBEC-KT) with AFT samples, harvested from subcutaneous tissue layer of 20 patients undergoing pulmonary metastasectomy, improved wound healing and cell proliferation indicating a trophic effect on both mesenchymal and epithelial cell types. Conversely AFT-conditioned medium was unable to stimulate in vitro proliferation of a lung adenocarcinoma reporter cellular system (A549). Moreover, co-injection of AFT and A549 cells in nude mice did not promote engraftment and progression of A549 cells. These preclinical findings provide preliminary evidence on the potential efficacy of AFT to accelerate lung tissue repair without undesired tumor promoting effects on putative residual cancer cells.

Posttranslational modification of proteins with the small ubiquitin-like modifier (SUMO) regulates protein function in the context of cell cycle and DNA repair. The occurrence of SUMOylation is less frequent as compared to protein modification with ubiquitin, and appears to be controlled by a smaller pool of conjugating and deconjugating enzymes. Mass spectrometry has been instrumental in defining specific as well as proteome-wide views of SUMO-dependent biological processes, and several methodological approaches have been developed in the recent past. Here, we provide an overview of the latest experimental approaches to the study of SUMOylation, and also describe hands-on protocols using a combination of biochemistry and mass spectrometry-based technologies to profile proteins that are SUMOylated in human cells.