The epithelium specific cell cycle regulator 14-3-3sigma is required for preventing entry into mitosis following ultraviolet B

iTRAQ-based quantitative proteomic analysis of differentially expressed proteins in chemoresistant nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a highly prevalent disease in Southeast Asia. The disease is typically diagnosed in the later stages, and chemotherapy resistance often causes treatment failure. To investigate the underlying mechanisms of drug resistance, we searched for chemoresistant-associated proteins in NPC and drug-resistant NPC cell lines using isobaric tags for relative and absolute quantitation combined with nano liquid chromatography-tandem mass spectrometry. The chemoresistant NPC cell lines CNE1DDP and CNE2DDP were resistant to 1 mg/L cisplatin, had resistant indexes of 4.58 and 2.63, respectively, and clearly grew more slowly than the NPC cell lines CNE1 and CNE2. Using three technical replicates, we identified 690 nonredundant proteins, 56 of which were differentially expressed in both groups of cell lines (CNE1 vs. CNE1DDP and CNE2 vs. CNE2DDP). Gene Ontology, KEGG pathway, and miRNA analyses and protein-protein interactions of differentially expressed proteins showed that proteins TRIM29, HSPB1, CLIC1, ANXA1, and STMN1, among others, may play a role in the mechanisms of chemoresistance in clinical therapy. The chemotherapy-resistant proteomic profiles obtained may allow the identification of novel biomarkers for early detection of chemoresistance in NPC and other cancers.

Characterization of Lgr5+ Progenitor Cell Transcriptomes after Neomycin Injury in the Neonatal Mouse Cochlea

Lgr5+ supporting cells (SCs) are enriched hair cell (HC) progenitors in the cochlea. Both in vitro and in vivo studies have shown that HC injury can spontaneously activate Lgr5+ progenitors to regenerate HCs in the neonatal mouse cochlea. Promoting HC regeneration requires the understanding of the mechanism of HC regeneration, and this requires knowledge of the key genes involved in HC injury-induced self-repair responses that promote the proliferation and differentiation of Lgr5+ progenitors. Here, as expected, we found that neomycin-treated Lgr5+ progenitors (NLPs) had significantly greater HC regeneration ability, and greater but not significant proliferation ability compared to untreated Lgr5+ progenitors (ULPs) in response to neomycin exposure. Next, we used RNA-seq analysis to determine the differences in the gene-expression profiles between the transcriptomes of NLPs and ULPs from the neonatal mouse cochlea. We first analyzed the genes that were enriched and differentially expressed in NLPs and ULPs and then analyzed the cell cycle genes, the transcription factors, and the signaling pathway genes that might regulate the proliferation and differentiation of Lgr5+ progenitors. We found 9 cell cycle genes, 88 transcription factors, 8 microRNAs, and 16 cell-signaling pathway genes that were significantly upregulated or downregulated after neomycin injury in NLPs. Lastly, we constructed a protein-protein interaction network to show the interaction and connections of genes that are differentially expressed in NLPs and ULPs. This study has identified the genes that might regulate the proliferation and HC regeneration of Lgr5+ progenitors after neomycin injury, and investigations into the roles and mechanisms of these genes in the cochlea should be performed in the future to identify potential therapeutic targets for HC regeneration.

Impact on Autophagy and Ultraviolet B Induced Responses of Treatment with the MTOR Inhibitors Rapamycin, Everolimus, Torin 1, and pp242 in Human Keratinocytes

The mechanistic target of Rapamycin (MTOR) protein is a crucial signaling regulator in mammalian cells that is extensively involved in cellular biology. The function of MTOR signaling in keratinocytes remains unclear. In this study, we detected the MTOR signaling and autophagy response in the human keratinocyte cell line HaCaT and human epidermal keratinocytes treated with MTOR inhibitors. Moreover, we detected the impact of MTOR inhibitors on keratinocytes exposed to the common carcinogenic stressors ultraviolet B (UVB) and UVA radiation. As a result, keratinocytes were sensitive to the MTOR inhibitors Rapamycin, everolimus, Torin 1, and pp242, but the regulation of MTOR downstream signaling was distinct. Next, autophagy induction only was observed in HaCaT cells treated with Rapamycin. Furthermore, we found that MTOR signaling was insensitive to UVB but sensitive to UVA radiation. UVB treatment also had no impact on the inhibition of MTOR signaling by MTOR inhibitors. Finally, MTOR inhibition by Rapamycin, everolimus, or pp242 did not affect the series of biological events in keratinocytes exposed to UVB, including the downregulation of BiP and PERK, activation of Histone H2A and JNK, and cleavage of caspase-3 and PARP. Our study demonstrated that MTOR inhibition in keratinocytes cannot always induce autophagy, and the MTOR pathway does not play a central role in the UVB triggered cellular response.

14-3-3σ Contributes to Radioresistance By Regulating DNA Repair and Cell Cycle via PARP1 and CHK2

14-3-3σ has been implicated in the development of chemo and radiation resistance and in poor prognosis of multiple human cancers. While it has been postulated that 14-3-3σ contributes to these resistances via inhibiting apoptosis and arresting cells in G₂-M phase of the cell cycle, the molecular basis of this regulation is currently unknown. In this study, we tested the hypothesis that 14-3-3σ causes resistance to DNA-damaging treatments by enhancing DNA repair in cells arrested in G₂-M phase following DNA-damaging treatments. We showed that 14-3-3σ contributed to ionizing radiation (IR) resistance by arresting cancer cells in G₂-M phase following IR and by increasing non-homologous end joining (NHEJ) repair of the IR-induced DNA double strand breaks (DSB). The increased NHEJ repair activity was due to 14-3-3σ-mediated upregulation of PARP1 expression that promoted the recruitment of DNA-PKcs to the DNA damage sites for repair of DSBs. On the other hand, the increased G₂-M arrest following IR was due to 14-3-3σ-induced Chk2 expression.Implications: These findings reveal an important molecular basis of 14-3-3σ function in cancer cell resistance to chemo/radiation therapy and in poor prognosis of human cancers. Mol Cancer Res; 15(4); 418-28. ©2017 AACR.