bims-apauto Biomed News
on Apoptosis and autophagy
Issue of 2021‒12‒26
eight papers selected by
Su Hyun Lee
Seoul National University

  1. Autophagy. 2021 Dec 19. 1-17
      Early events during development leading to exit from a pluripotent state and commitment toward a specific germ layer still need in depth understanding. Autophagy has been shown to play a crucial role in both development and differentiation. This study employs human embryonic and induced pluripotent stem cells to understand the early events of lineage commitment with respect to the role of autophagy in this process. Our data indicate that a dip in autophagy facilitates exit from pluripotency. Upon exit, we demonstrate that the modulation of autophagy affects SOX2 levels and lineage commitment, with induction of autophagy promoting SOX2 degradation and mesendoderm formation, whereas inhibition of autophagy causes SOX2 accumulation and neuroectoderm formation. Thus, our results indicate that autophagy-mediated SOX2 turnover is a determining factor for lineage commitment. These findings will deepen our understanding of development and lead to improved methods to derive different lineages and cell types.Abbreviations: ACTB: Actin, beta; ATG: Autophagy-related; BafA1: Bafilomycin A1; CAS9: CRISPR associated protein 9; CQ: Chloroquine; DE: Definitive endoderm; hESCs: Human Embryonic Stem Cells; hiPSCs: Human Induced Pluripotent Stem Cells; LAMP1: Lysosomal Associated Membrane Protein 1; MAP1LC3: Microtubule-Associated Protein 1 Light Chain 3; MTOR: Mechanistic Target Of Rapamycin Kinase; NANOG: Nanog Homeobox; PAX6: Paired Box 6; PE: Phosphatidylethanolamine; POU5F1: POU class 5 Homeobox 1; PRKAA2: Protein Kinase AMP-Activated Catalytic Subunit Alpha 2; SOX2: SRY-box Transcription Factor 2; SQSTM1: Sequestosome 1; ULK1: unc-51 like Autophagy Activating Kinase 1; WDFY3: WD Repeat and FYVE Domain Containing 3.
    Keywords:  Autophagosome; SOX2; differentiation; ectoderm; endoderm; mesoderm; pluripotent stem cells
  2. Autophagy. 2021 Dec 22. 1-3
      Macroautophagy/autophagy is an evolutionarily conserved catabolic pathway required to maintain cellular homeostasis. In cancer, the tumor cell-intrinsic effects of autophagy are highly context specific, which could promote cancer cell survival or induce programmed cell death. Here, we reveal that OLR1/LOX-1 (oxidized low density lipoprotein receptor 1), a scavenger receptor highly expressed in esophageal cancer cells, is involved in tumorigenesis by suppressing autophagic cell death. Mechanistically, OLR1 binding to RACK1 activates MAP2K/MEK-MAPK/ERK signaling leading to TFEB (transcription factor EB) being trapped outside the nucleus and inhibiting autophagy. In addition, we identify a polysaccharide which causes the degradation of OLR1 and suppresses this autophagic pathway to inhibit tumorigenesis. This study demonstrates novel molecular mechanisms underlying the tumor-suppressive effect of autophagy and provides therapeutic insight for esophageal cancer.
    Keywords:  Cell death; ERK; RACK1; TFEB; fucoidan; tumorigenesis
  3. Autophagy. 2021 Dec 19. 1-3
      Mitophagy, a type of selective autophagy targeting damaged or superfluous mitochondria, is critical to maintain cell homeostasis. Besides the well-characterized PRKN-dependent mitophagy, PRKN-independent mitophagy also plays significant physiological roles. In a recent study, researchers from Anne Simonsen's lab discovered two lipid binding kinases, GAK and PRKCD, as positive regulators of PRKN-independent mitophagy. The researchers further investigated how these two proteins regulate mitophagy and demonstrated their roles in vivo. Focusing on the less known PRKN-independent mitophagy regulators, these findings shed light on understanding the mechanism of mitophagy and its relation to diseases.
    Keywords:  Autophagy; GAK; PRKCD; PRKN; lipid-binding kinases
  4. J Biol Chem. 2021 Dec 17. pii: S0021-9258(21)01324-7. [Epub ahead of print] 101514
      Recognition of human autophagy-related 8 (hATG8) proteins by autophagy receptors represents a critical step within this major cellular quality control system. Autophagy impairment is known to be a pathogenic mechanism in the motor neuron disorder amyotrophic lateral sclerosis (ALS). However, overlapping but specific roles of hATG8 proteins belonging to the LC3 and GABARAP subfamilies are incompletely understood, and binding selectivity is typically overlooked. We previously showed an ALS-associated variant of the SQSTM1/p62 (p62) autophagy receptor bearing an L341V mutation within its ATG8-interacting motif (AIM) impairs recognition of LC3B in vitro, yielding an autophagy-deficient phenotype. Improvements in understanding the molecular basis of hATG8 recognition by AIMs now distinguish LC3-interaction and GABARAP-interaction motifs and predict the effects of L341V substitution may extend beyond loss-of-function to biasing AIM binding preference. Through biophysical analyses, we confirm impaired binding of the L341V-AIM mutant to LC3A, LC3B, GABARAP, and GABARAPL1. In contrast, p62 AIM interactions with LC3C and GABARAPL2 are unaffected by this mutation. Isothermal titration calorimetry and NMR investigations provided insights into the entropy-driven GABARAPL2/p62 interaction and how the L341V mutation may be tolerated. Competition binding also demonstrated reduced association of the L341V-AIM with one hATG8 manifests as a relative increase in association with alternate hATG8s, indicating effective reprogramming of hATG8 selectivity. These data highlight how a single AIM peptide might compete for binding with different hATG8s, and suggest the L341V-AIM mutation may be neomorphic, representative of a disease mechanism that likely extends into other human disorders.
    Keywords:  AIM; SQSTM1/p62; amyotrophic lateral sclerosis; autophagy; hATG8
  5. EMBO J. 2021 Dec 23. e108823
      Polyubiquitination by E2 and E3 enzymes is crucial to cell cycle control, epigenetic regulation, and development. The hallmark of the E2 family is the ubiquitin (Ub)-conjugating (UBC) domain that forms a dynamic thioester conjugate with ubiquitin (E2~Ub). Numerous studies have focused on E2 surfaces, such as the N-terminal and crossover helices, that directly interact with an E3 or the conjugated ubiquitin to stabilize the active, "closed" state of the E2~Ub. However, it remains unclear how other E2 surfaces regulate ubiquitin transfer. Here, we demonstrate the helix-turn-helix (HTH) motif of the UBC tunes the intrinsic polyubiquitination activity through distinct functions in different E2s. Interestingly, the E2HTH motif is repurposed in UBE2S and UBE2R2 to interact with the conjugated or acceptor ubiquitin, respectively, modulating ubiquitin transfer. Furthermore, we propose that Anaphase-Promoting Complex/Cyclosome binding to the UBE2SHTH reduces the conformational space of the flexible E2~Ub, demonstrating an atypical E3-dependent activation mechanism. Altogether, we postulate the E2HTH motif evolved to provide new functionalities that can be harnessed by E3s and permits additional regulation to facilitate specific E2-E3-mediated polyubiquitination.
    Keywords:  Anaphase-Promoting Complex/Cyclosome; E2 ubiquitin-conjugating enzyme; RING E3 ubiquitin ligase; UBE2R; UBE2S
  6. J Pept Sci. 2021 Dec 22. e3389
      Aberrant activation of the Wnt signaling pathway has been identified in numerous types of cancer. One common feature of oncogenic Wnt regulation involves an increase in the cellular levels of β-catenin due to interference with its constitutive ubiquitin-dependent degradation. Targeting β-catenin has therefore emerged as an appealing approach for the treatment of Wnt-dependent cancers. Here, we report a strategy that employs multifunctional stapled peptides to recruit an E3 ubiquitin ligase to β-catenin, thereby rescuing β-catenin degradation by hijacking the endogenous ubiquitin-proteasome pathway. Specifically, we designed, synthesized, and evaluated a panel of multifunctional stapled peptides that have a β-catenin binding moiety (StAx-35) covalently linked to a second stapled peptide moiety (SAH-p53-8), which is capable to interact with the E3 ubiquitin ligase MDM2. We found that in vitro these multifunctional peptides can recruit the MDM2 protein to β-catenin and induce poly-ubiquitination on β-catenin. In cellulo, treatment of the human colorectal cancer cell line SW480 with the multifunctional stapled peptides showed dose-dependent degradation of endogenous β-catenin levels. In addition, a luciferase reporter assay showed that the multifunctional stapled peptides can suppress β-catenin-mediated gene expression via the Wnt signaling pathway. Therefore, these multifunctional stapled peptides provide a unique research tool for examining the Wnt signaling pathway by targeted knockdown of β-catenin at the protein level, and may serve as leads for potential drug candidates in the treatment of Wnt-dependent cancers.
    Keywords:  Wnt signaling pathway; degradation; multifunctional stapled peptide; ubiquitination; β-catenin
  7. Cells. 2021 Nov 25. pii: 3309. [Epub ahead of print]10(12):
      Cancer immunotherapies, including immune checkpoint inhibitors and immune pathway-targeted therapies, are promising clinical strategies for treating cancer. However, drug resistance and adverse reactions remain the main challenges for immunotherapy management. The future direction of immunotherapy is mainly to reduce side effects and improve the treatment response rate by finding new targets and new methods of combination therapy. Ubiquitination plays a crucial role in regulating the degradation of immune checkpoints and the activation of immune-related pathways. Some drugs that target E3 ubiquitin ligases have exhibited beneficial effects in preclinical and clinical antitumor treatments. In this review, we discuss mechanisms through which E3 ligases regulate tumor immune checkpoints and immune-related pathways as well as the opportunities and challenges for integrating E3 ligases targeting drugs into cancer immunotherapy.
    Keywords:  E3 ubiquitin ligase; cancer immunotherapy; immune checkpoints; immune signaling pathway