Sequential Phosphorylation of Hepatitis C Virus NS5A Protein Requires the ATP-Binding Domain of NS3 Helicase.

The propagation of the hepatitis C virus (HCV) is regulated in part by the phosphorylation of its nonstructural protein NS5A that undergoes sequential phosphorylation on several highly conserved serine residues and switches from a hypo- to a hyperphosphorylated state. Previous studies have shown that NS5A sequential phosphorylation requires NS3 encoded on the same NS3-NS4A-NS4B-NS5A polyprotein. Subtle mutations in NS3 without affecting its protease activity could affect NS5A phosphorylation.

Autophagy restricts mitochondrial DNA damage-induced release of ENDOG (endonuclease G) to regulate genome stability.

Genotoxic insult causes nuclear and mitochondrial DNA damages with macroautophagy/autophagy induction. The role of mitochondrial DNA (mtDNA) damage in the requirement of autophagy for nuclear DNA (nDNA) stability is unclear. Using site-specific DNA damage approaches, we show that specific nDNA damage alone does not require autophagy for repair unless in the presence of mtDNA damage.

Sequential S232/S235/S238 Phosphorylation of the Hepatitis C Virus Nonstructural Protein 5A.

The hepatitis C virus (HCV) protein NS5A is a phosphorylated protein with crucial roles in viral replication and assembly. NS5A was thought to undergo sequential phosphorylation on a series of conserved serine residues; however, the phosphorylation cascade remained obscure. Using three phosphorylation-specific antibodies, we found that phosphorylation at S232, S235, and S238 occurred in parallel in HCV-infected Huh7.

Serine 235 Is the Primary NS5A Hyperphosphorylation Site Responsible for Hepatitis C Virus Replication.

The nonstructural protein 5A (NS5A) of the hepatitis C virus (HCV) is a phosphoprotein with two phosphorylation states: hypo- and hyperphosphorylation. Genetic mutation studies have demonstrated a cluster of serine residues responsible for NS5A hyperphosphorylation and functions in viral replication and assembly; however, the phosphorylation levels and potential interactions among the serine residues are unclear. We used three specific antibodies to measure NS5A phosphorylation at S222, S235, and S238 that were identified in our previous proteomics study.

Phosphorylation of Serine 235 of the Hepatitis C Virus Non-Structural Protein NS5A by Multiple Kinases.

Phosphorylation at serine 235 (S235) of the hepatitis C virus (HCV) non-structural protein 5A (NS5A) plays a critical role in the viral life cycle. For medical and virological interests, we exploited the HEK293T kidney cells to test 3 candidate protein kinases on NS5A S235 phosphorylation. Inhibitors that inhibit casein kinase I α (CKIα), polo-like kinase I (PlKI) or calmodulin-dependent kinase II (CaMKII) all reduced NS5A S235 phosphorylation.

Phosphoproteomics Identified an NS5A Phosphorylation Site Involved in Hepatitis C Virus Replication.

The non-structural protein 5A (NS5A) is a hepatitis C virus (HCV) protein indispensable for the viral life cycle. Many prior papers have pinpointed several serine residues in the low complexity sequence I region of NS5A responsible for NS5A phosphorylation; however, the functions of specific phosphorylation sites remained obscure. Using phosphoproteomics, we identified three phosphorylation sites (serines 222, 235, and 238) in the NS5A low complexity sequence I region.