Camptothecin-induced downregulation of MLL5 contributes to the activation of tumor suppressor p53

Abstract

Mixed lineage leukemia 5 (MLL5) has been implicated in multiple aspects of cell physiology, such as hematopoiesis, cell cycle control and chromatin regulatory network. In this study, we present evidence that MLL5 is involved in the camptothecin (CPT)-induced p53 activation. CPT promoted the degradation of MLL5 protein in a time-and dose-dependent manner in actively replicating cells. The downregulation of MLL5 led to phosphorylation of p53 at Ser392, which was abrogated by exogenous overexpression of MLL5. In MLL5-knockdown cells, p53 protein was stabilized and bound to DNA with higher affinity, leading to activation of downstream genes. Co-immunoprecipitation showed that MLL5 preferentially interacted with the tetramerized form of p53, and knockdown of MLL5 promoted chromatin accumulation of p53 tetramers, suggesting that the association of MLL5 with p53 may prevent the p53 tetramers from binding to the chromatin target sites. The role of MLL5 in CPT-induced p53 activation was conserved in developing zebrafish, where CPT downregulated zebrafish Mll5 protein, and the microinjection of zebrafish mll5 mRNA substantially blocked the CPT-induced apoptosis. In summary, our study proposed MLL5 as a novel component in the regulation of p53 homeostasis and a new cellular determinant of CPT.

Transposon mutagenesis identifies genes driving hepatocellular carcinoma in a chronic hepatitis B mouse model

“…Two genes including Zbtb20 34,35 and Ankrd17 36,37 are involved in hepatocyte differentiation and maturation, while Zbtb20 is a transcription factor that represses the expression of α-fetoprotein, a widely used biomarker used for HCC surveillance. The Setd2 TS gene 38 and the putative TS genes Adk 39 , Dpyd 40,41 , Mll5 42 and Nfia 43,44 were also identified as potential driver genes for HCC, although there is no published evidence they are involved in HCC. Six driver genes also regulate hepatic metabolism with Pten 45 , Gsk3b 46 , Adk 47,48 , Zbtb20 49 and Ghr 50,51 regulating lipid and glucose metabolism, and Dpyd controling pyrimidine catabolism in hepatocytes.…”

Solution NMR Structure and Histone Binding of the PHD Domain of Human MLL5

“…Immunoprecipitation and in-vitro pull down experiments showed that MLL5 interacts with borealin, a subunit of the chromosome passenger complex, stabilizing the complex [18]. MLL5 is also reported to bind with tetrameric p53 via p53's DNA binding domain [19]. MLL5 is a component of a complex associated with retinoic acid receptor that requires GlcNAcylation of its SET domain in order to activate its histone lysine methyltransferase activity [20].…”

Click synthesis of a polyamidoamine dendrimer-based camptothecin prodrug

“…18, 31 We performed cell cycle analyses following treatment with PBS, free CPT, CPT-G4.5-PEG or dendrimer carrier. As shown in Figure 6, cells treated with free CPT or CPT-G4.5-PEG conjugate exhibited a remarkable decrease in the G 0 /G 1 cell population and an increase in G 2 /M going from a little more than 20% to more than 40% over a period of 24 h. Untreated cells (PBS group) showed a normal cell cycle distribution with a larger fraction in the G 0 /G 1 phase.…”

“…1-3 Thus, various dendrimer-based drug delivery platforms have been developed 4-7 , and their utility for delivering anticancer drugs _ENREF_18 _ENREF_19 has been actively explored and yielded promising results. 8-14 _ENREF_20 _ENREF_18 Regardless, a commonly encountered problem is the heterogeneity of ligand and drug on the dendrimer surface during chemical synthesis. 15 It is essential to obtain a uniform distribution of ligand and drug for standardizing therapeutic effects and for the successful translation of dendrimer-based nanomedicines to clinical application.…”