Jeanho Yun

BACKGROUND: Glucose deprivation, a feature of poorly vascularized solid tumors, activates the unfolded protein response (UPR), a stress-signaling pathway, in tumor cells. We recently isolated a novel macrocyclic compound, versipelostatin (VST), that inhibits transcription from the promoter of GRP78, a gene that is activated as part of the UPR. We examined the effect of VST on the UPR induced by glucose deprivation or other stressors and on tumor growth in vivo. METHODS: Human colon cancer HT-29, fibrosarcoma HT1080, and stomach cancer MKN74 cells were cultured in the absence of glucose or in the presence of glucose and a UPR-inducing chemical stressor (the N-glycosylation inhibitor tunicamycin, the calcium ionophore A23187, or the hypoglycemia-mimicking agent 2-deoxyglucose [2DG]). The effect of VST on UPR induction was determined by reverse transcription-polymerase chain reaction and immunoblot analysis of the UPR target genes GRP78 and GRP94; by immunoblot analysis of the UPR transcriptional activators ATF6, XBP1, and ATF4; and by analyzing reporter gene expression in cells transiently transfected with a GRP78 promoter-reporter gene. Cell sensitivity to VST was examined with a colony formation assay and flow cytometry. In vivo antitumor activity of VST was assessed with an MKN74 xenograft model. RESULTS: VST inhibited expression of UPR target genes in glucose-deprived or 2DG-treated cells but not in cells treated with tunicamycin or A23187. VST also inhibited the production of the UPR transcriptional activators XBP1 and ATF4 during glucose deprivation. The UPR-inhibitory action of VST was seen only in conditions of glucose deprivation and caused selective and massive killing of the glucose-deprived cells. VST alone and in combination with cisplatin statistically significantly (P =.004 and P<.001 for comparisons with untreated control, respectively) inhibited tumor growth of MKN74 xenografts. CONCLUSION: Disruption of the UPR may provide a novel therapeutic approach to targeting glucose-deprived solid tumors.

Mitophagy is a process of selective removal of damaged or unnecessary mitochondria using autophagic machinery. Mitophagy plays an essential role in maintaining mitochondrial quality control and homeostasis. Mitochondrial dysfunctions and defective mitophagy in neurodegenerative diseases, cancer, and metabolic diseases indicate a close link between human disease and mitophagy. Furthermore, recent studies showing the involvement of mitophagy in differentiation and development, suggest that mitophagy may play a more active role in controlling cellular functions. A better understanding of mitophagy will provide insights about human disease and offer novel chance for treatment. This review mainly focuses on the recent implications for mitophagy in human diseases and normal physiology. [BMB Reports 2017; 50(6): 299-307].

The p53 tumor suppressor protein regulates the transcription of regulatory genes involved in cell cycle arrest and apoptosis. We have reported previously that inducible expression of the p53 gene leads to the cell cycle arrest both at G(1) and G(2)/M in association with induction of p21 and reduction of mitotic cyclins (cyclin A and B) and cdc2 mRNA. In this study, we investigated the mechanism by which p53 regulates transcription of the cdc2 gene. Transient transfection analysis showed that wild type p53 represses whereas various dominant negative mutants of p53 increase cdc2 transcription. The cdc2 promoter activity is not repressed in cells transfected with a transactivation mutant, p53(22/23). An adenovirus oncoprotein, E1B-55K inhibits the p53-mediated repression of the cdc2 promoter, while E1B-19K does not. Since the cdc2 promoter does not contain a TATA sequence, we performed deletion and point mutation analyses and identified the inverted CCAAT sequence located at -76 as a cis-acting element for the p53-mediated regulation. We found that a specific DNA-protein complex is formed at the CCAAT sequence and that this complex contains the NF-Y transcription factor. Consistently, a dominant negative mutant of the NF-YA subunit, NF-YAm29, decreases the cdc2 promoter, and p53 does not further decrease the promoter activity in the presence of NF-YAm29. These results suggest that p53 negatively regulates cdc2 transcription and that the NF-Y transcription factor is required for the p53-mediated regulation.