Crosstalk between p38 MAPK and GR Signaling.

The p38 MAPK is a signaling pathway important for cells to respond to environmental and intracellular stress. Upon activation, the p38 kinase phosphorylates downstream effectors, which control the inflammatory response and coordinate fundamental cellular processes such as proliferation, apoptosis, and differentiation. Dysregulation of this signaling pathway has been linked to inflammatory diseases and cancer. Secretion of glucocorticoids (GCs) is a classical endocrine response to stress. The glucocorticoid receptor (GR) is the primary effector of GCs and plays an important role in the regulation of cell metabolism and immune response by influencing gene expression in response to hormone-dependent activation. Its ligands, the GCs or steroids, in natural or synthetic variation, are used as standard therapy for anti-inflammatory treatment, severe asthma, autoimmune diseases, and several types of cancer. Several years ago, the GR was identified as one of the downstream targets of p38, and, at the same time, it was shown that glucocorticoids could influence p38 signaling. In this review, we discuss the role of the crosstalk between the p38 and GR in the regulation of gene expression in response to steroids and comprehend the importance and potential of this interplay in future clinical applications.

Hepatitis B Virus Exploits ERGIC-53 in Conjunction with COPII to Exit Cells.

Several decades after its discovery, the hepatitis B virus (HBV) still displays one of the most successful pathogens in human populations worldwide. The identification and characterization of interactions between cellular and pathogenic components are essential for the development of antiviral treatments. Due to its small-sized genome, HBV highly depends on cellular functions to produce and export progeny particles. Deploying biochemical-silencing methods and molecular interaction studies in HBV-expressing liver cells, we herein identified the cellular ERGIC-53, a high-mannose-specific lectin, and distinct components of the endoplasmic reticulum (ER) export machinery COPII as crucial factors of viral trafficking and egress. Whereas the COPII subunits Sec24A, Sec23B and Sar1 are needed for both viral and subviral HBV particle exit, ERGIC-53 appears as an exclusive element of viral particle propagation, therefore interacting with the N146-glycan of the HBV envelope in a productive manner. Cell-imaging studies pointed to ER-derived, subcellular compartments where HBV assembly initiates. Moreover, our findings provide evidence that HBV exploits the functions of ERGIC-53 and Sec24A after the envelopment of nucleocapsids at these compartments in conjunction with endosomal sorting complexes required for transport (ESCRT) components. These data reveal novel insights into HBV assembly and trafficking, illustrating therapeutic prospects for intervening with the viral life cycle.

Hepatitis B Virus Subverts the Autophagy Elongation Complex Atg5-12/16L1 and Does Not Require Atg8/LC3 Lipidation for Viral Maturation.

Previous studies indicated that hepatitis B virus (HBV) stimulates autophagy to favor its production. To understand how HBV co-opts autophagy as a proviral machinery, we studied the roles of key autophagy proteins in HBV-replicating liver cell cultures. RNA interference-mediated silencing of Atg5, Atg12, and Atg16L1, which promote autophagophore expansion and LC3 membrane conjugation, interfered with viral core/nucleocapsid (NC) formation/stability and strongly diminished virus yields. Concomitantly, the core/NC membrane association and their sorting to envelope-positive compartments were perturbed. A close inspection of the HBV/autophagy cross talk revealed that the virus depended on Atg12 covalently conjugated to Atg5. In support of this finding, HBV required the E2-like enzymes Atg10 and Atg3, which catalyze or facilitate Atg5-12 conjugation, respectively. Atg10 and Atg3 knockdowns decreased HBV production, while Atg3 overexpression increased virus yields. Mapping analyses demonstrated that the HBV core protein encountered the Atg5-12/16L1 complex via interaction with the intrinsically disordered region of the Atg12 moiety that is dispensable for autophagy function. The role of Atg12 in HBV replication was confirmed by its incorporation into virions. Although the Atg5-12/16L1 complex and Atg3 are essential for LC3 lipidation and, thus, for autophagosome maturation and closure, HBV propagation did not require LC3. Silencing of LC3B, the most abundant LC3 isoform, did not inhibit but rather augmented virus production. Similar augmenting effects were obtained upon overexpression of a dominant negative mutant of Atg4B that blocked the lipid conjugation of the LC3 isoforms and their GABARAP paralogues. Together, our data indicate that HBV subverts early, nondegradative autophagy components as assembly scaffolds, thereby concurrently avoiding autophagosomal destruction.IMPORTANCE Infections with the hepatitis B virus (HBV), an enveloped pararetrovirus, cause about 1 million deaths per year, as current therapies rarely achieve a cure. Understanding the HBV life cycle and concomitant host cell interactions is instrumental to develop new antiviral concepts. Here, we proceeded to dissect the roles of the autophagy machinery in virus propagation. By using RNA interference and overexpression studies in HBV-replicating cell lines, we identified the autophagic Atg5-12/16L1 elongation complex along with Atg10 and Atg3 to be an essential scaffold for HBV nucleocapsid assembly/stability. Deficits in Atg5-12/16L1 and Atg10/Atg3, which normally drive autophagophore membrane expansion, strongly impaired progeny virus yields. HBV gained access to Atg5-12/16L1 via interaction of its core protein with the Atg12 moiety of the complex. In contrast, subsequent autophagosome maturation and closure events were unnecessary for HBV replication, as evidenced by inhibition of Atg8/LC3 conjugation. Interfering with the HBV/Atg12 cross talk may be a tool for virus control.