Distinct role of 4E-BP1 and S6K1 in regulating autophagy and hepatitis B virus (HBV) replication

Pd/C-catalyzed regiodivergent hydrocarboxylation and esterification of alkynes

An unprecedented and highly reactive Pd/C catalytic system has been introduced for the regiodivergent hydrocarboxylation of terminal alkynes to selectively afford various acrylic and cinnamic acids employing oxalic acid as a CO source as well as a promoter for the formation of the active Pd-H complex. Herein, the formation of cinnamic acid is proposed to follow a unique anti-Markovnikov hydroiodination mechanism and the formation of acrylic acid might follow the traditional hydrocarboxylation pathway. Additionally, internal alkynes undergo hydrocarboxylation and carbonylative esterification with aliphatic alcohols to yield different α,β-unsaturated acids and esters respectively. The designed strategies were successfully leveraged for a diverse class of α,β-unsaturated acids and esters with excellent selectivity and yields under mild reaction conditions. Furthermore, the acid functionalization of complicated naturally derived alkynes, utilizing economical and bench-stable oxalic acid and a commercially accessible reusable catalyst with gram-scale applicability are the additional benefits of the established protocol.

An Overview of the Unfolded Protein Response (UPR) and Autophagy Pathways in Human Viral Oncogenesis

Autophagy and Unfolded Protein Response (UPR) can be regarded as the safe keepers of cells exposed to intense stress. Autophagy maintains cellular homeostasis, ensuring the removal of foreign particles and misfolded macromolecules from the cytoplasm and facilitating the return of the building blocks into the system. On the other hand, UPR serves as a shock response to prolonged stress, especially Endoplasmic Reticulum Stress (ERS), which also includes the accumulation of misfolded proteins in the ER. Since one of the many effects of viral infection on the host cell machinery is the hijacking of the host translational system, which leaves in its wake a plethora of misfolded proteins in the ER, it is perhaps not surprising that UPR and autophagy are common occurrences in infected cells, tissues, and patient samples. In this book chapter, we try to emphasize how UPR, and autophagy are significant in infections caused by six major oncolytic viruses-Epstein-Barr (EBV), Human Papilloma Virus (HPV), Human Immunodeficiency Virus (HIV), Human Herpesvirus-8 (HHV-8), Human T-cell Lymphotropic Virus (HTLV-1), and Hepatitis B Virus (HBV). Here, we document how whole-virus infection or overexpression of individual viral proteins in vitro and in vivo models can regulate the different branches of UPR and the various stages of macro autophagy. As is true with other viral infections, the relationship is complicated because the same virus (or the viral protein) exerts different effects on UPR and Autophagy. The nature of this response is determined by the cell types, or in some cases, the presence of diverse extracellular stimuli. The vice versa is equally valid, i.e., UPR and autophagy exhibit both anti-tumor and pro-tumor properties based on the cell type and other factors like concentrations of different metabolites. Thus, we have tried to coherently summarize the existing knowledge, the crux of which can hopefully be harnessed to design vaccines and therapies targeted at viral carcinogenesis.

The unique Akt inhibitor SC66 suppressed AMPK activity and abolished autophagy through the EGFR-p62 pathway

Akt is usually considered to be a negative regulator of both autophagy and adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) signaling. In the present study, we found that SC66, a pyridine-based allosteric Akt inhibitor, suppressed basal and H₂ O₂ -induced autophagy concurrent with decreased phosphorylation and activity of AMPK. SC66 treatment led to the formation of a high molecular weight (HMW) form of SQSTM1/p62 (p62), which is an autophagic substrate and is essential for selective autophagy. Moreover, we observed that SC66 inhibited the binding of p62 and microtubule-associated protein light chain 3 (LC3). The immunoprecipitation results revealed the interaction between p62 and epidermal growth factor receptor (EGFR), and knockdown of EGFR reversed SC66-mediated autophagy inhibition without affecting the phosphorylation of acetyl-CoA carboxylase (ACC), a well-known substrate of AMPK. SC66 increased the interaction between EGFR and Beclin 1 and markedly decreased the association of EGFR with VPS34, a critical protein for autophagy induction. Collectively, the data presented here indicate that EGFR-p62 pathway plays a critical role in Akt-mediated positive regulation of autophagy.

HBx induces hepatocellular carcinogenesis through ARRB1-mediated autophagy to drive the G1/S cycle

The hepatitis B virus X protein (HBx) is involved in the process of hepatocellular carcinoma via the activation of various oncogenes. Our previous study indicated that ARBB1 (arrestin beta 1) promotes hepatocellular carcinogenesis (HCC). However, the role of ARRB1 in HBx-related HCC remains unclear. Herein, we identified that ARRB1 was upregulated by HBx in vivo and in vitro. Arrb1 deficiency suppressed HBx-induced hepatocellular carcinogenesis in several mouse models. Furthermore, knockdown of ARRB1 blocked HBx-induced macroautophagic/autophagic flux and disrupted the formation of autophagosomes. ARRB1 interacted with HBx, and the autophagic core protein MAP1LC3/LC3, a scaffolding protein, was essential for complete autophagy. Inhibition of autophagy by 3-methyladenine or interference of ATG5 or ATG7 attenuated HBx-induced cell cycle acceleration and the subsequent proliferative response via the induction of G₁/S arrest. The absence of autophagy abolished the phosphorylation of CDK2 and the activity of the CDK2-CCNE1 complex. Our results demonstrate that ARRB1 plays a critical role in HBV-related HCC via modulating autophagy and the CDKN1B-CDK2-CCNE1-E2F1 axis and indicate that ARRB1 may be a potential therapeutic target for HCC.

Hepatitis B Surface Antigen Suppresses the Activation of Nuclear Factor Kappa B Pathway via Interaction With the TAK1-TAB2 Complex

Chronic hepatitis B is a major health problem worldwide, with more than 250 million chronic carriers. Hepatitis B virus interferes with the host innate immune system so as to evade elimination via almost all of its constituent proteins; nevertheless, the function of HBsAg with respect to immune escape remains unclear. This study aimed to determine the role HBsAg plays in assisting HBV to escape from immune responses. We found that HBsAg suppressed the activation of the nuclear factor kappa B (NF-кB) pathway, leading to downregulation of innate immune responses. HBsAg interacted with TAK1 and TAB2 specifically, inhibiting the phosphorylation and polyubiquitination of TAK1 and the K63-linked polyubiquitination of TAB2. Autophagy is a major catabolic process participating in many cellular processes, including the life cycle of HBV. We found that HBsAg promoted the autophagic degradation of TAK1 and TAB2 via the formation of complexes with TAK1 and TAB2, resulting in suppression of the NF-κB pathway. The expression of TAK1, TAB2, and the translocation of NF-κB inversely correlated with HBsAg levels in clinical liver tissues. Taken together, our findings suggest a novel mechanism by which HBsAg interacts with TAK1-TAB2 complex and suppresses the activation of NF-κB signaling pathway via reduction of the post-translational modifications and autophagic degradation.

Enterovirus 71 induces autophagy in mice via mTOR inhibition and ERK pathway activation

AIMS

Enterovirus 71 (EV71) is one of the main viruses that cause hand-foot-mouth disease; however, its pathogenic mechanism remains unclear. This study characterized the relationship between EV71 infection and autophagy in vivo and explored the molecular mechanism underlying EV71-induced autophagy.

MATERIALS AND METHODS

A mouse model of EV71 infection was prepared by intraperitoneally injecting one-day-old BALB/c suckling mice with 30 μL/g of EV71 virus stock solution for 3 days. The behavior, fur condition, weight, and mice mortality were monitored, and disease scores were calculated. The pathological damage to the brain, lung, and muscle tissues after the viral infection was assessed by hematoxylin and eosin staining. Western blot and immunofluorescence analyses were used to detect the expression levels of viral protein 1, Beclin-1, microtubule-associated protein light chain 3B, mammalian target of rapamycin (mTOR), phosphorylated (p)-mTOR, extracellular signal-regulated protein kinase (ERK) 1/2, and p-ERK.

KEY FINDINGS

EV71 infection can trigger autophagy in the brains, lungs, and muscles of infected mice. The autophagy response triggered by EV71 is achieved by the simultaneous mTOR inhibition and the ERK pathway activation. Blocking the mTOR pathway may aggravate autophagy, whereas ERK inhibition alleviates autophagy but cannot completely prevent it.

SIGNIFICANCE

EV71 infection can induce autophagy in mice, involving mTOR and ERK signaling pathways. These two signaling pathways are independent and do not interfere with each other.

S6K1 inhibits HBV replication through inhibiting AMPK-ULK1 pathway and disrupting acetylation modification of H3K27

AIMS

To investigated the effect of S6K1 on the replication and transcription of HBV DNA using multiple cell models.

MAIN METHODS

The pgRNA, total HBV RNA and HBV DNA level were detected by Real-time PCR. The HBcAg expression by Western blot and the activity of four HBV promoters, such as preS1, preS2/S, core, and X promoters by using dual luciferase reporter assay. Moreover, we determined S6K1 interacted with HBcAg in both cytoplasm and nucleus through Immunofluorescence, co-immunoprecipitation (CoIP) and Western blot.

KEY FINDINGS

S6K1 inhibited HBV DNA replication and cccDNA-dependent transcription in HBV-expressing stable cell lines. The mechanistic study revealed that S6K1 suppressed HBV DNA replication by inhibiting AMPK-ULK1 autophagy pathway, and the nuclear S6K1 suppressed HBV cccDNA-dependent transcription by inhibiting the acetylation modification of H3K27. In addition, HBV capsid protein (HBcAg) suppressed the phosphorylation level of S6K1Thr389 by interacting with S6K1, indicating a viral antagonism of S6K1-mediated antiviral mechanism.

SIGNIFICANCE

The p70 ribosomal S6 kinase (S6K1) is a serine/threonine protein kinase, and it plays a significant role in different cellular processes. It has been previously reported that S6K1 affects hepatitis B virus (HBV) replication but the underlying mechanism remains unclear. In this study, our data suggested that the activation of S6K1 restricts HBV replication through inhibiting AMPK-ULK1 autophagy pathway and H3K27 acetylation. These findings indicated that S6K1 might be a potential therapeutic target for HBV infection.

Different Role of Raptor and Rictor in Regulating Rasfonin-Induced Autophagy and Apoptosis in Renal Carcinoma Cells

Both Raptor and Rictor are the key components in the complexes of mammalian target of rapamycin (mTOR), which play a vital role in mediating autophagy. Unlike mTOR, the regulatory role of either Raptor or Rictor in the regulation of autophagic process is relatively less explored. In present study, we found that rasfonin, which isolated from Talaromyces sp. 3656-A1 and was a fungal natural product, activated both caspase-dependent apoptosis and autophagy in ACHN, a renal carcinoma cell line. Knockdown of Raptor decreased both rasfonin-induced autophagic flux and PARP-1 cleavage, and in contrast, Rictor silencing increased apoptosis concomitantly enhancing rasfonin-induced autophagy. Unexpectedly, API-2, which was widely used as an inhibitor of Akt, promoted rasfonin-dependent autophagy in Raptor-depleted but not Rictor-deprived cells. Collectively, these results demonstrated that Raptor and Rictor could play a distinctly regulatory role in rasfonin-enhanced autophagy and apoptosis.

Autophagy Regulation by the Translation Machinery and Its Implications in Cancer

Various metabolic pathways and molecular processes in the cell act intertwined, and dysregulating the interplay between some of them may lead to cancer. It is only recently that defects in the translation process, i.e., the synthesis of proteins by the ribosome using a messenger (m)RNA as a template and translation factors, have begun to gain strong attention as a cause of autophagy dysregulation with effects in different maladies, including cancer. Autophagy is an evolutionarily conserved catabolic process that degrades cytoplasmic elements in lysosomes. It maintains cellular homeostasis and preserves cell viability under various stress conditions, which is crucial for all eukaryotic cells. In this review, we discuss recent advances shedding light on the crosstalk between the translation and the autophagy machineries and its impact on tumorigenesis. We also summarize how this interaction is being the target for novel therapies to treat cancer.