All-trans retinoic acid induces autophagic degradation of ubiquitin-like modifier activating enzyme 3 in acute promyelocytic leukemia cells

Retinoic acid alleviates rotavirus-induced intestinal damage by regulating redox homeostasis and autophagic flux in piglets

Rotaviruses (RV) are a major cause of severe gastroenteritis, particularly in neonatal piglets. Despite the availability of effective vaccines, the development of antiviral therapies for RV remains an ongoing challenge. Retinoic acid (RA), a metabolite of vitamin A, has been shown to have anti-oxidative and antiviral properties. However, the mechanism by which RA exerts its intestinal-protective and antiviral effects on RV infection is not fully understood. The study investigates the effects of RA supplementation in Duroc × Landrace × Yorkshire (DLY) piglets challenged with RV. Thirty-six DLY piglets were assigned into six treatments, including a control group, RA treatment group with two concentration gradients (5 and 15 mg/d), RV treatment group, and RV treatment group with the addition of different concentration gradients of RA (5 and 15 mg/d). Our study revealed that RV infection led to extensive intestinal architecture damage, which was mitigated by RA treatment at lower concentrations by increasing the villus height and villus height/crypt depth ratio (P < 0.05), enhancing intestinal stem cell signaling and promoting intestinal barrier functions. In addition, 15 mg/d RA supplementation significantly increased NRF2 and HO-1 protein expression (P < 0.05) and GSH content (P < 0.05), indicating that RA supplementation can enhance anti-oxidative signaling and redox homeostasis after RV challenge. Additionally, the research demonstrated that RA exerts a dual impact on the regulation of autophagy, both stimulating the initiation of autophagy and hindering the flow of autophagic flux. Through the modulation of autophagic flux, RA influence the progression of RV infection. These findings provide new insights into the regulation of redox hemostasis and autophagy by RA and its potential therapeutic application in RV infection.

UBA3 promotes the occurrence and metastasis of intrahepatic cholangiocarcinoma through MAPK signaling pathway

Intrahepatic cholangiocarcinoma (ICC) accounts for approximately 15% of primary liver cancers, and the incidence rate has been increasing in recent years. Surgical resection is the best treatment for ICC, but the 5-year survival rate is less than 30%. ICC signature genes are crucial for the early diagnosis of ICC, so it is especially important to identify signature genes. The aim of this study is to screen the signature genes of ICC and find the potential target for the treatment of ICC. We find that UBA3 is highly expressed in ICC, and knockdown of UBA3 inhibits ICC proliferation, invasion and migration. Mechanistic experiments show that UBA3 promotes ICC proliferation, invasion and migration by affecting ANXA2 through the MAPK signaling pathway. UBA3 is a target of bufalin, and bufalin targeting UBA3 inhibits ICC development and progression through the MAPK signaling pathway. In conclusion, our study shows that bufalin inhibits ICC by targeting UBA3, which has emerged as a new biomarker and potential therapeutic target for ICC.

Profilin upregulation induces autophagy through stabilization of AMP-activated protein kinase

Profilin regulates actin polymerization, and its balanced expression is required for cellular growth and development. Most tumors have compromised profilin expression, and its overexpression in MDA MB-231 breast cancer cells has been reported to activate AMP-activated protein kinase α (AMPKα), an energy-sensing molecule that affects various cellular processes including autophagy. The present study aims to explore the role of profilin in inducing autophagy. We employed all-trans retinoic acid (ATRA) as an inducer of profilin expression and showed that profilin induces autophagy through mTOR inhibition, autophagy-activating kinase ULK1 upregulation, and AMPK stabilization as well as its activation. Furthermore, evidence from our study indicates physical interaction between profilin and AMPK, which results in AMPK stabilization and induction of prolonged autophagy, thereby leading to apoptosis. This study uncovers a novel mechanism that induces autophagy in triple-negative breast cancer cells.

Diverse and pivotal roles of neddylation in metabolism and immunity

Neddylation is one type of protein post-translational modification by conjugating a ubiquitin-like protein neural precursor cell-expressed developmentally downregulated protein 8 to substrate proteins via a cascade involving E1, E2, and E3 enzymes. The best-characterized substrates of neddylation are cullins, essential components of cullin-RING E3 ubiquitin-ligase complexes. The discovery of noncullin neddylation targets indicates that neddylation may have diverse biological functions. Indeed, neddylation has been implicated in various cellular processes including cell cycle progression, metabolism, immunity, and tumorigenesis. Here, we summarized the reported neddylation substrates and also discuss the functions of neddylation in the immune system and metabolism.

Autophagy regulates lipid production and contributes to the sebosuppressive effect of retinoic acid in human SZ95 sebocytes

BACKGROUND

Autophagy is a catabolic process for eliminating damaged organelles or proteins to maintain cellular homeostasis. Recently, lipids have been demonstrated to be targets for autophagosomal degradation. Therefore, autophagy might be involved in sebaceous gland homeostasis, however, relevant data are lacking.

OBJECTIVES

We investigated the role of autophagy in sebaceous lipogenesis and its regulatory mechanisms in human SZ95 sebocytes. We also examined the possible role of autophagy in 13-cis-retinoic acid (13-cis-RA)-mediated sebosuppression.

METHODS

Autophagy markers expression was examined by immunohistochemistry in normal and acne lesional skin. SZ95 sebocytes were treated with autophagy inhibitors under starvation or treated with a combination of testosterone and linoleic acid (testosterone/LA), with or without autophagy inducer rapamycin or 13-cis-RA. Lipids were assessed by BODIPY and quantitative Nile Red staining. Autophagy-related gene 7 small interference RNA was used to confirm the role of autophagy on the sebosuppressive effect of rapamycin or 13-cis-RA.

RESULTS

Autophagy markers were strongly expressed in the maturing sebaceous gland cells in healthy skin, whereas downregulated in the acne-involved sebaceous glands. Testosterone/LA or insulin-like growth factor-1 inhibited starvation-induced sebocyte autophagy. Pharmacological inhibition of autophagy led to increased sebaceous lipid accumulation. Contrary, rapamycin inhibited the testosterone/LA-induced lipogenesis and expression of fatty acid synthesis genes via activating the autophagy pathway. 13-cis-RA increased autophagy in SZ95 sebocytes, partly via FoxO1 activation, and inhibition of autophagy abolished the sebosuppressive effect of 13-cis-RA.

CONCLUSIONS

Autophagy plays an important role in the modulation of lipogenesis in human sebocytes and is involved in the sebostatic effect of 13-cis-RA.

Retinoic acid worsens ATG10-dependent autophagy impairment in TBK1-mutant hiPSC-derived motoneurons through SQSTM1/p62 accumulation

Mutations in the TBK1 (TANK binding kinase 1) gene are causally linked to amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). TBK1 phosphorylates the cargo receptors OPTN and SQSTM1 regulating a critical step in macroautophagy/autophagy. Disruption of the autophagic flux leads to accumulation of cytosolic protein aggregates, which are a hallmark of ALS. hiPSC-derived TBK1-mutant motoneurons (MNs) showed reduced TBK1 levels and accumulation of cytosolic SQSTM1-positive aggresomes. By screening a library of nuclear-receptor-agonists for modifiers of the SQSTM1 aggregates, we identified 4-hydroxy(phenyl)retinamide (4HPR) as a potent modifier exerting detrimental effects on mutant-TBK1 motoneurons fitness exacerbating the autophagy overload. We have shown by TEM that TBK1-mutant motoneurons accumulate immature phagophores due a failure in the elongation phase, and 4HPR further worsens the burden of dysfunctional phagophores. 4HPR-increased toxicity was associated with the upregulation of SQSTM1 in a context of strongly reduced ATG10, while rescue of ATG10 levels abolished 4HPR toxicity. Finally, we showed that 4HPR leads to a downregulation of ATG10 and to an accumulation of SQSTM1⁺ aggresomes also in hiPSC-derived C9orf72-mutant motoneurons. Our data show that cultured human motoneurons harboring mutations in TBK1 gene display typical ALS features, like decreased viability and accumulation of cytosolic SQSTM1-positive aggresomes. The retinoid 4HPR appears a strong negative modifier of the fitness of TBK1 and C9orf72-mutant MNs, through a pathway converging on the mismatch of initiated autophagy and ATG10 levels. Thus, autophagy induction appears not to be a therapeutic strategy for ALS unless the specific underlying pathway alterations are properly addressed. Abbreviations: 4HPR: 4-hydroxy(phenyl)retinamide; AKT: AKT1 serine/threonine kinase 1; ALS: amyotrophic lateral sclerosis; ATG: autophagy related; AVs: autophagic vesicle; C9orf72: chromosome 9 open reading frame 72; CASP3: caspase 3; CHAT: choline O-acetyltransferase; CYCS: cytochrome c, somatic; DIV: day in vitro; FTD: frontotemporal dementia; FUS: FUS RNA binding protein; GFP: green fluorescent protein; hiPSCs: human induced pluripotent stem cells; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MNs: motoneurons; mRFP: monomeric red fluorescent protein; MTOR: mechanistic target of rapamycin kinase; NFE2L2/NRF2: nuclear factor, erythroid 2 like 2; RARA: retinoic acid receptor alpha; SLC18A3/VACHT: solute carrier family 18 (vesicular acetylcholine transporter), member 3; SQSTM1/p62: sequestosome 1; TBK1: TANK binding kinase 1; TEM: transmission electron microscopy.

RACK1 deficiency synergizes with all-trans retinoic acid to induce apoptosis in human acute promyelocytic leukemia cells

As a classic differentiation agent, all-trans retinoic acid (ATRA) has been widely used in the treatment of acute promyelocytic leukemia (APL). However, the clinical application of ATRA has strict limitations, for its severe side effects due to the accumulation of peripheral blood leukocytes. The scaffold protein RACK1 (Receptor for activated C kinase 1), which regulates multiple signaling pathways, has been proposed to contribute to the survival of leukemic progenitors. But it remains unclear whether it is also involved in the oncogenic growth of APL. In the present study, we demonstrate that silencing of endogenous RACK1 expression synergized with ATRA to promote the death of NB4 and HL-60 APL cells without effect on cell differentiation induced by ATRA. Interestingly, RACK1 knockdown combined with ATRA treatment mainly induces apoptosis. It is distinct to the necrotic cell death induced by idarubicin in combination with ATRA, a regimen extensively used in the clinic to prevent neutrophil accumulation. Further exploration revealed that the lysosome-autophagy pathway is likely to be responsible for the anti-apoptotic role of RACK1. Taken together, our findings indicate that RACK1 is essential in maintaining the malignant features of APL, and targeting RACK1 may have promising therapeutic implications in the treatment of APL.

[Changes in autophagy during maturation and differentiation of Hepa1-6 cells induced by all-trans retinoic acid]

OBJECTIVE

To investigate the effects of different concentrations of all-trans retinoic acid (ATRA) on the maturation, differentiation and autophagy of Hepa1-6 cells.

MONTHOD

Hepa1-6 cells were treated with 0.1, 1, and 10 µmol/L ATRA, and the changes in the expressions of hepatic specific markers were detected using real-time PCR and Western blotting. Indocyanine green (ICG) and periodic acid-schiff (PAS) staining was used to assess the functional maturation of Hepa1-6 cells, and the cell-cell junction and autophagy were observed under transmission electron microscopy to determine the optimal concentration of ATRA for treatment. The expressions of autophagy-related markers in the cells were detected using Western blotting, and confocal microscopy was used to observe the autophagic flow in the cells transfected with ptfLC3 plasmid.

RESULTS

Compared with the control cells, the hepatocytes treated with ATRA showed a concentration-dependent decrease in AFP expression and increase in the expressions of ALB, CK18, TAT and ApoB. ICG and PAS staining revealed significantly increased number of positive cells after ATRA treatment. Following ATRA treatment, the cells exhibited obviously increased tight junctions, cytoskeleton and number of autophagosomes under transmission electron microscopy. ATRA treatment resulted in significantly increased the expressions of autophagy-related markers LC3-II, Beclin-1, RAB7 and P62 and also an increased ratio of LC3-II/LC3-I(P<0.05). Confocal microscopy revealed obviously increased green and red spots in the cells after ATRA treatment.

CONCLUSION

ATRA can induce the maturation and differentiation and enhance the level of autophagy in Hepa1-6 cells.

Protein neddylation and its alterations in human cancers for targeted therapy

Neddylation, a post-translational modification that conjugates an ubiquitin-like protein NEDD8 to substrate proteins, is an important biochemical process that regulates protein function. The best-characterized substrates of neddylation are the cullin subunits of Cullin-RING ligases (CRLs), which, as the largest family of E3 ubiquitin ligases, control many important biological processes, including tumorigenesis, through promoting ubiquitylation and subsequent degradation of a variety of key regulatory proteins. Recently, increasing pieces of experimental evidence strongly indicate that the process of protein neddylation modification is elevated in multiple human cancers, providing sound rationale for its targeting as an attractive anticancer therapeutic strategy. Indeed, neddylation inactivation by MLN4924 (also known as pevonedistat), a small molecule inhibitor of E1 NEDD8-activating enzyme currently in phase I/II clinical trials, exerts significant anticancer effects by inducing cell cycle arrest, apoptosis, senescence and autophagy in a cell-type and context dependent manner. Here, we summarize the latest progresses in the field with a major focus on preclinical studies in validation of neddylation modification as a promising anticancer target.