Sirtuin protein family member 3 (Sirt3) has been suggested as a positive regulator in alleviating oxidative stress by acting on the mitochondrial antioxidant machinery in solid tumors; however, its role and regulation in hematological malignancies has been poorly understood. Here, we show that contrary to what has been reported in solid tumors, in K562 leukemia cells elevated Sirt3 was associated with mitochondrial stress, and depletion of Sirt3 decreased reactive oxygen species (ROS) generation and lipid oxidation, but increased the ratio of reduced glutathione (GSH) to oxidized glutathione (GSSG), suggesting an opposite role of Sirt3 in regulating oxidative stress in the leukemia cells. Notably, loss of autophagy by deletion of autophagy essential gene or by pharmacological inhibition on autophagic degradation caused a significant accumulation of Sirt3. However, induced activation of autophagy did not cause autophagic degradation of Sirt3. Furthermore, inhibiting proteasome activity accumulated Sirt3 in autophagy-intact but not autophagy-defective cells, and disrupting functional autophagy either genetically or pharmacologically caused significantly less ubiquitination of Sirt3. Therefore, our data suggest that basal but not enhanced autophagy activity maintains ubiquitination-proteasomal degradation of Sirt3 to limit lipid oxidative stress, representing an adaptive mechanism by which autophagy, in collaboration with the ubiquitination-proteasomal system, controls oxidative stress by controlling the levels of certain proteins in K562 leukemia cells.

Several clinical trials revealed that estrogen receptor (ER) status had relevance to the response of mammary malignancy to chemotherapy. Autophagy has emerged as an important cellular mechanism of tumor cells in response to anticancer therapy. The aim of this study is to investigate whether gemcitabine induces autophagy, and more importantly, whether such autophagy is functional relevant to the therapeutic effects of gemcitabine in breast cancer cells in relation to the ER status. In our study, autophagy was induced both in ER+ MCF-7 and ER- MDA-MB-231 cells by gemcitabine markedly, while the autophagy plays distinct roles - cytoprotective in ER- MDA-MB-231 and cytotoxic in ER+ MCF-7 cells. Gemcitabine treatment leads to the activation of ERα-ERK-P62 signal pathway in MCF-7 cells which may augment the autophagic degradation, thus results in the excessive activation of autophagy and irreversible autophagic cell death eventually. Inhibition of ERα-ERK-P62 cascades in MCF-7 cells by small interfering RNA or PD98059 impairs the autophagic degradation, and leads to "autophagic switch" - from cytotoxic autophagy to cytoprotection. Moreover, stable overexpression of ERα in the ER- BCap37 breast cancer cell line enhances the gemcitabine-induced autophagy flux and switches the autophagic cytoprotection in ER- BCap37 to cytotoxicity effect in ER+ BCap37 cells. Our study firstly demonstrated that ER status influences gemcitabine efficacy via modulating the autophagy in breast cancer cells.

Pancreatic cancer is one of the most lethal human diseases, with an all-stage 5-year survival rate below 5%. To date, no effective and specific therapy is available for this disease. Mutations in KRAS are frequently reported in pancreatic and many other cancers; thus, KRAS is an attractive therapeutic target. Our objective was to specifically eliminate mutant KRAS and induce cell death of tumors expressing this mutant protein. We thus constructed several chimeric proteins by connecting the C-terminal domains of several adaptor proteins of E3 ubiquitin ligases such as CBL, CHIP, E6AP, and VHL, as well as VIF encoded by human immunodeficiency virus type 1 (HIV-1), to the Ras binding domain (RBD) of Raf. Although all of these chimeric proteins caused the degradation of mutant KRAS and the death of KRAS-mutant-tumor cell lines, the RBD-VIF with a protein transduction domain (PTD), named PTD-RBD-VIF, had the strongest tumor-killing effect. Intraperitoneally administered recombinant PTD-RBD-VIF potently inhibited the growth of xenografted KRAS-mutant pancreatic cancer cells. Our findings indicate that recombinant PTD-RBD-VIF, a chimeric protein with a combined cellular-viral origin, could be further developed for the treatment of various tumors harboring mutant or over-activated KRAS, especially for cases presenting with pancreatic cancer recurrence after surgery.