PHF23 negatively regulates the autophagy of chondrocytes in osteoarthritis.

AIM: Osteoarthritis (OA) is the main cause of disability and joint replacement surgery in the elderly. As a crucial cell survival mechanism, autophagy has been reported to decrease in OA. PHF23 is a new autophagy inhibitor which was first reported by us previously. This study aimed to explore the anti-autophagic mechanism of PHF23 to make it a possible therapeutic target of OA. MAIN METHOD: Lentiviral vectors specific to PHF23 were used on chondrocytes (C28/I2) to establish PHF23 overexpressed or knockdown stable cell strains. Interleukin (IL)-1ß (10 ng/mL) and chloroquine (CQ, 25 uM) were used as an inducer of OA and inhibitor of lysosome, respectively. Autophagy was evaluated by autophagosome formation using transmission electron microscopy (TEM) and western blot analysis of P62 and LC3B on different groups of cells. Effects of PHF23 on OA were evaluated by collagen II immunofluorescent staining and western blot analysis of OA-associated proteins MMP13 and ADAMTS5. Effects of PHF23 on AMPK and mTOR/S6K pathways and mitophagy were determined by western blot analysis. KEY FINDINGS: Knockdown of PHF23 enhanced IL-1ß-induced autophagy, while overexpression of PHF23 exerted the opposite effect. Knockdown of PHF23 protected chondrocytes against IL-1ß-induced OA by decreasing the levels of OA-associated proteins and increasing expression of Collagen II. Knockdown of PHF23 also increased mitophagy level and altered the phosphorylation levels of AMPK, mTOR, and S6K. SIGNIFICANCE: PHF23 downregulates autophagy, mitophagy in IL-1ß-induced OA-like chondrocytes and alters the activities of AMPK and mTOR/S6K, which suggests that PHF23 may be a possible therapeutic target for OA.

Disulfram Treatment of NUP98-PHF23 AML Is Not Effective In Vivo: Potential Role for Hematopoietic Stem Cells Niche / 임상소아혈액종양

BACKGROUND: NUP98 has numerous partner genes of which plant homeodomain (PHD) finger protein 23 (PHF23) fusion with NUP98 (NP23) can be detected by RT-PCR in patients with cytogenetically normal acute myelogenous leukemia (AML). In this fusion transcript of NP23 PHD of PHF23 is known to specifically bind H3K4me3 residues and act as a chromatic modifier. Disulfiram (DSF) which inhibits the binding of PHD to H3K4me3 residues selectively killed NP23 myeloblasts in vitro and therefore, we planned to evaluate the efficacy of DSF in vivo. METHODS: Cultured 961C cells (CD45.2), NP23 myeloblast cells were transplanted into B57BL/6 mice (CD45.1). Using limit dilution assay the number of leukemic stem cells (LSCs) could be calculated. A certain amount of 961C cells were transplanted into B57BL/6 mice and DSF was treated after 1 week. The engraftment level was monitored with CD45.2. Kaplan Meier survival curve was used to compare the survival between therapeutic and control group. RESULTS: 961C cells could be transplanted without radiation in recipient mice. Calculated LSC was estimated to be 1 out of 184 cells (95% CI range, 56–609). When treated with DSF of different doses and administration routes in 961C recipient mice no survival advantage of DSF was observed in 961C transplanted immunocompetent mouse, however it was evident that engraftment level was consistent in both groups. CONCLUSION: No survival advantage of DSF in 961C transplanted immunocompetent mouse was observed, however it was evident that 961C cells shared niche with normal hematopoietic stem cells (HSCs). We expect that 961C cells and transplanted recipient mice have the potential to be used as in vivo system for new drugs development as well as for research dealing with niche for normal HSCs and LSCs.

A cryptic translocation leading to NUP98-PHF23 fusion in AML.

Chromosome translocations leading to gene fusions have emerged as important oncogenic drivers of various types of malignancies. Detection and characterization of these fusion genes not only help diagnosis and management of specific malignancies, but also contribute to our understanding of the genetic basis and pathogenesis of these diseases. NUP98 gene encodes a 98 kDa nucleoporin, which is a component of the nuclear pore complex that mediates transport of mRNA and proteins between the nucleus and the cytoplasm. Due to its participation in translocations leading to the formation of fusion with at least 29 different partner genes, NUP98 is considered one of the most promiscuous fusion genes in hematologic malignancies. We discuss our identification and characterization of a NUP98-PHF23 fusion from a cryptic translocation in patients with acute myeloid leukemia (AML).

NUP98-PHF23 fusion is recurrent in acute myeloid leukemia and shares gene expression signature of leukemic stem cells.

Chromosome translocations involving nucleoporin 98 gene (NUP98) have been identified in a wide array of hematologic malignancies, and the resulting NUP98-associated fusions are known to play a critical role in leukemogensis through dysregulation of gene expression. Although NUP98-associated fusions were initially thought to be rare, application of molecular technologies has revealed that cryptic translocations involving NUP98 are more frequent than previously appreciated. We report an additional case of t(11;17)(p15;p13) resulting in the fusion of NUP98 and plant homeodomain finger 23 (PHF23) in a pediatric patient with acute myeloid leukemia (AML). Using RNA sequencing, we determined in-frame fusion points and also analyzed the gene expression profile of NUP98-PHF23 positive AML. Gene set enrichment analysis (GSEA) demonstrates that NUP98-PHF23 fusion shares gene expression signature of NUP98-HOXA9 fusion, the prototype of the NUP98-associated fusions, as well as the signature of leukemic stem cells. To our knowledge this is the first transcriptome analysis of human samples with NUP98-PHF23 positive AML. Our findings are in support of the gene expression study of NUP98-PHF23 mouse model and validate the usefulness of the mouse model in developing therapeutic strategies for the treatment of subsets of AML.

PHF23 (plant homeodomain finger protein 23) negatively regulates cell autophagy by promoting ubiquitination and degradation of E3 ligase LRSAM1.

Autophagy is a multistep process that involves the degradation and digestion of intracellular components by the lysosome. It has been proved that many core autophagy-related molecules participate in this event. However, new component proteins that regulate autophagy are still being discovered. At present, we report PHF23 (PHD finger protein 23) with a PHD-like zinc finger domain that can negatively regulate autophagy. Data from experiments indicated that the overexpression of PHF23 impaired autophagy, as characterized by decreased levels of LC3B-II and weakened degradation of endogenous and exogenous autophagic substrates. Conversely, knockdown of PHF23 resulted in opposite effects. Molecular mechanism studies suggested that PHF23 interacts with LRSAM1, which is an E3 ligase key for ubiquitin-dependent autophagy against invading bacteria. PHF23 promotes the ubiquitination and proteasome degradation of LRSAM1. We also show that the PHD finger of PHF23 is a functional domain needed for the interaction with LRSAM1. Altogether, our results indicate that PHF23 is a negative regulator associated in autophagy via the LRSAM1 signaling pathway. The physical and functional connection between the PHF23 and LRSAM1 needs further investigation.