Autophagy and tumorigenesis

Autophagy, or cellular self-digestion, is activated in cancer cells in response to multiple stresses and has been demonstrated to promote tumor cell survival and drug resistance. Nonetheless, genetic evidence supports that autophagy functions as a tumor suppressor mechanism. Hence, the precise role of autophagy during cancer progression and treatment is both tissue and context dependent. Here, we discuss our current understanding of the biological functions of autophagy during cancer development, overview how autophagy is regulated by cancer-associated signaling pathways, and review how autophagy inhibition is being exploited to improve clinical outcomes.     

Estimation of the target stem-cell population size in chronic myeloid leukemogenesis

Estimation of the number of hematopoietic stem cells capable of causing chronic myeloid leukemia (CML) is relevant to the development of biologically based risk models of radiation-induced CML. Through a comparison of the age structure of CML incidence data from the Surveillance, Epidemiology, and End Results (SEER) Program and the age structure of chromosomal translocations found in healthy subjects, the number of CML target stem cells is estimated for individuals above 20 years of age. The estimation involves three steps. First, CML incidence among adults is fit to an exponentially increasing function of age. Next, assuming a relatively short waiting time distribution between BCR-ABL induction and the appearance of CML, an exponential age function with rate constants fixed to the values found for CML is fitted to the translocation data. Finally, assuming that translocations are equally likely to occur between any two points in the genome, the parameter estimates found in the first two steps are used to estimate the number of target stem cells for CML. The population-averaged estimates of this number are found to be 1.86×10⁸ for men and 1.21×10⁸ for women; the 95% confidence intervals of these estimates are (1.34×10⁸, 2.50×10⁸) and (0.84×10⁸, 1.83×10⁸), respectively. Received: 3 March 1999 / Accepted in revised form: 7 May 1999     

Nε-carboxymethyllysine-mediated endoplasmic reticulum stress promotes endothelial cell injury through Nox4/MKP-3 interaction

N^ε-carboxymethyllysine (CML) is an important driver of diabetic vascular complications and endothelial cell dysfunction. However, how CML dictates specific cellular responses and the roles of protein tyrosine phosphatases and ERK phosphorylation remain unclear. We examined whether endoplasmic reticulum (ER) localization of MAPK phosphatase-3 (MKP-3) is critical in regulating ERK inactivation and promoting NADPH oxidase-4 (Nox4) activation in CML-induced endothelial cell injury. We demonstrated that serum CML levels were significantly increased in type 2 diabetes patients and diabetic animals. CML induced ER stress and apoptosis, reduced ERK activation, and increased MKP-3 protein activity in HUVECs and SVECs. MKP-3 siRNA transfection, but not that of MKP-1 or MKP-2, abolished the effects of CML on HUVECs. Nox4-mediated activation of MKP-3 regulated the switch to ERK dephosphorylation. CML also increased the integration of MKP-3 with ERK, which was blocked by silencing MKP-3. Exposure of antioxidants abolished CML-increased MKP-3 activity and protein expression. Furthermore, immunohistochemical staining of both MKP-3 and CML was increased, but phospho-ERK staining was decreased in the aortic endothelium of streptozotocin-induced and high-fat diet-induced diabetic mice. Our results indicate that an MKP-3 pathway might regulate ERK dephosphorylation through Nox4 during CML-triggered endothelial cell dysfunction/injury, suggesting that therapeutic strategies targeting the Nox4/MKP-3 interaction or MKP-3 activation may have clinical implications for diabetic vascular complications.     

FUBP3 regulates chronic myeloid leukaemia progression through PRC2 complex regulated PAK1-ERK signalling

The development of resistance and heterogeneity in differential response towards tyrosine kinase inhibitors (TKI) in chronic myeloid leukaemia (CML) treatment has led to the exploration of factors independent of the Philadelphia chromosome. Among these are the association of deletions of genes on derivative (der) 9 chromosome with adverse outcomes in CML patients. However, the functional role of genes near the breakpoint on der (9) in CML prognosis and progression remains largely unexplored. Copy number variation and mRNA expression were evaluated for five genes located near the breakpoint on der (9). Our data showed a significant association between microdeletions of the FUBP3 gene and its reduced expression with poor prognostic markers and adverse response outcomes in CML patients. Further investigation using K562 cells showed that the decrease in FUBP3 protein was associated with an increase in proliferation and survival due to activation of the MAPK–ERK pathway. We have established a novel direct interaction of FUBP3 protein and PRC2 complex in the regulation of ERK signalling via PAK1. Our findings demonstrate the role of the FUBP3 gene located on der (9) in poor response and progression in CML with the identification of additional druggable targets such as PAK1 in improving response outcomes in CML patients.     

Application of the direct beta counter Matrix 96 for cytotoxic assays: Simultaneous processing and reading of 96 wells using a51Cr-retention assay

To assess the cytotoxic activity of immune cells, we have developed a⁵¹Cr-retention assay in which the radioactivity retained by⁵¹Cr-labeled target cells, following coincubation with cytotoxic cells, is monitored using the automated Matrix 96 beta counter. The Matrix 96 is designed for simultaneously counting 96 samples isolated from a 96-well microplate. It uses 96 uniform and independent detectors operating on the principle of avalanche gas ionization in the Geiger-Muller mode. Samples must be dry because the detectors are of the open-window type. Therefore, samples from the 96 wells of the microplate are simultaneously harvested onto a filter using the MicroMate 196, a 96-well cell harvester, dried and quantified in the Matrix 96. Usually the⁵¹Cr isotope is measured by the detection of gamma radiation in gamma counters. The Matrix 96, however, monitors Auger electrons, which are also emitted by⁵¹Cr. We have shown that the retention assay can be used to monitor the cytotoxic activity of activated lymphocytes including lymphokine-activated killer cells and tumor-infiltrating lymphocytes against various tumor cell lines. This assay is most suitable for experiments in which low E/T ratios are sufficient to detect highly cytotoxic cells, such as clone screening in cloning assays or in limiting-dilution analysis assays. These assays involve processing and reading large numbers of microplates. In this case, the retention assay monitored in the Matrix 96 will improve the work flow and decrease the amount of radioactive waste.This work was supported by the American Cancer Society grant IN-162-C     

An ent‐Kaurane Diterpenoid Isolated from Rabdosia excisa Suppresses Bcr‐Abl Protein Expression in Vitro and in Vivo and Induces Apoptosis of CML Cells

Chronic myelogenous leukemia (CML) is a disease of the blood stem cells that features the oncoprotein Bcr‐Abl. Tyrosine kinase inhibitors (TKIs) are used to treat CML patients, but these have limited efficacy due to the emergence of resistance via genetic mutation. Kamebakaurin is an ent‐kaurane diterpenoid that has been isolated from Rabdosia excisa (Maxim .) H.Hara . Herein, we investigate the potential of kamebakaurin as a chemotherapy reagent for the treatment of CML. We conducted in vitro and in vivo biological experiments and found that kamebakaurin potently inhibits cell proliferation, mainly by enhancing cell apoptosis and down‐regulating Bcr‐Abl protein levels. In addition, kamebakaurin was found to inhibit tumor growth and has no side effects on five internal organs for in vivo experiment. These results suggest that kamebakaurin is a potential anticancer agent and is a key compound for further investigations.