BackgroundLoss of endothelial cell integrity and selective permeability barrier is an early event in the sequence of oxidant-mediated injury and may result in atherosclerosis, hypertension and facilitation of transendothelial migration of cancer cells during metastasis. We already reported that endothelial cell integrity is tightly regulated by the balanced co-activation of p38 and ERK pathways. In particular, we showed that phosphorylation of tropomyosin-1 (tropomyosin alpha-1 chain = Tm1) at Ser283 by DAP kinase, downstream of the ERK pathway might be a key event required to maintain the integrity and normal functions of the endothelium in response to oxidative stress.MethodsEndothelial permeability was assayed by monitoring the passage of Dextran-FITC through a tight monolayer of HUVECs grown to confluence in Boyden chambers. Actin and Tm1 dynamics and distribution were evaluated by immunofluorescence. We modulated the expression of Tm1 by siRNA and lentiviral-mediated expression of wild type and mutated forms of Tm1 insensitive to the siRNA. Transendothelial migration of HT-29 colon cancer cells was monitored in Boyden chambers similarly as for permeability.ResultsWe provide evidence indicating that Tm1 phosphorylation at Ser283 is essential to regulate endothelial permeability under oxidative stress by modulating actin dynamics. Moreover, the transendothelial migration of colon cancer cells is also regulated by the phosphorylation of Tm1 at Ser283.ConclusionOur finding strongly support the role for the phosphorylation of endothelial Tm1 at Ser283 to prevent endothelial barrier dysfunction associated with oxidative stress injury.

Extravasation of circulating cancer cells is a key event of metastatic dissemination that is initiated by the adhesion of cancer cells to vascular endothelial cells. It requires the interaction between adhesion receptors such as E-selectin present on endothelial cells and their ligands on cancer cells. Notably, E-selectin influences the metastatic potential of breast, bladder, gastric, pancreatic, and colorectal carcinoma as well as of leukemia and lymphoma. Here, we show that E-selectin expression induced by the pro-inflammatory cytokine IL-1β is directly and negatively regulated by miR-31. The transcription of miR-31 is activated by IL-1β. This activation depends on p38 and JNK MAP kinases, and their downstream transcription factors GATA2, c-Fos and c-Jun. The miR-31-mediated repression of E-selectin impairs the metastatic potential of colon cancer cells by decreasing their adhesion to, and migration through, the endothelium. These results highlight for the first time that microRNA mediates E-selectin-dependent extravasation of colon cancer cells.

Stress granules (SG) are cytoplasmic RNA granules that form during various types of stress known to inhibit general translation, including oxidative stress, hypoxia, endoplasmic reticulum stress (ER), ionizing radiations or viral infection. Induction of these SG promotes cell survival in part through sequestration of proapoptotic molecules, resulting in the inactivation of cell death pathways. SG also form in cancer cells, but studies investigating their formation upon treatment with chemotherapeutics are very limited. Here we identified Lapatinib (Tykerb / Tyverb ®), a tyrosine kinase inhibitor used for the treatment of breast cancers as a new inducer of SG in breast cancer cells. Lapatinib-induced SG formation correlates with the inhibition of general translation initiation which involves the phosphorylation of the translation initiation factor eIF2α through the kinase PERK. Disrupting PERK-SG formation by PERK depletion experiments sensitizes resistant breast cancer cells to Lapatinib. This study further supports the assumption that treatment with anticancer drugs activates the SG pathway, which may constitute an intrinsic stress response used by cancer cells to resist treatment.