Obatoclax, a pan-inhibitor of anti-apoptotic Bcl-2 proteins, exhibits cytotoxic effect on cancer cells through both apoptosis-dependent and -independent pathways. Here we show that obatoclax caused cytotoxicity in both cisplatin-sensitive and -resistant esophageal cancer cells. Although obatoclax showed differential apoptogenic effects in these cells, it consistently blocked autophagic flux, which was evidenced by concomitant accumulation of LC3-II and p62. Obatoclax was trapped in lysosomes and induced lysosome clustering. Obatoclax also substantially reduced the expression of lysosomal cathepsins B, D and L. Moreover, cathepsin knockdown was sufficient to induce cytotoxicity, connecting lysosomal function to cell viability. Consistent with the known function of autophagy, obatoclax caused the accumulation of polyubiquitinated proteins and showed synergy with proteasome inhibition. Taken together, our studies unveiled impaired lysosomal function as a novel mechanism whereby obatoclax mediates its cytotoxic effect in esophageal cancer cells.

No abstract

Mutations in the human myeloproliferative leukemia (MPL) protein gene are known to cause congenital amegakaryocytic thrombocytopenia (CAMT). The prognosis of this heritable disorder is poor and bone marrow transplantation is the only effective treatment. Here, by using the TALEN (transcription activator-like effector nuclease) technology, we created a zebrafish mpl mutant to model human CAMT. Disruption of zebrafish mpl lead to a severe reduction in thrombocytes and a high bleeding tendency, as well as deficiencies in adult hematopoietic stem/progenitor cells. We further demonstrated that thrombocytopenia in mpl mutant zebrafish was caused by impaired Tpo/Mpl/Jak2 signaling, resulting in reduced proliferation of thrombocyte precursors. These results indicate that mpl mutant zebrafish develop thrombocytopenia resembling the human CAMT. To utilize fully zebrafish to study thrombocyte biology and thrombocytopenia disorders, we generated a transgenic reporter line Tg(mpl:eGFP)smu4, in which green fluorescent protein (GFP) expression was driven by the mpl promoter. Detailed characterization of Tg(mpl:eGFP)smu4 fish confirmed that the thrombocyte lineage was specifically marked by GFP expression. In conclusion, we generated the first transmissible congenital thrombocytopenia zebrafish model mimicking human CAMT and a thrombocyte-specific transgenic line. Together with Tg(mpl:eGFP)smu4, mpl mutant zebrafish provide a useful tool for drug screening and study of thrombocytopoiesis.

No abstract

No abstract