Significance of hepatitis B virus capsid dephosphorylation via polymerase

BACKGROUND

It is generally believed that hepatitis B virus (HBV) core protein (HBc) dephosphorylation (de-P) is important for viral DNA synthesis and virion secretion. HBV polymerase contains four domains for terminal protein, spacer, reverse transcriptase, and RNase H activities.

METHODS

HBV Polymerase mutants were transfected into HuH-7 cells and assayed for replication and HBc de-P by the Phos-tag gel analysis. Infection assay was performed by using a HepG2-NTCP-AS2 cell line.

RESULTS

Here, we show that a novel phosphatase activity responsible for HBc de-P can be mapped to the C-terminal domain of the polymerase overlapping with the RNase H domain. Surprisingly, while HBc de-P is crucial for viral infectivity, it is essential for neither viral DNA synthesis nor virion secretion. The potential origin, significance, and mechanism of this polymerase-associated phosphatase activity are discussed in the context of an electrostatic homeostasis model. The Phos-tag gel analysis revealed an intriguing pattern of "bipolar distribution" of phosphorylated HBc and a de-P HBc doublet.

CONCLUSIONS

It remains unknown if such a polymerase-associated phosphatase activity can be found in other related biosystems. This polymerase-associated phosphatase activity could be a druggable target in clinical therapy for hepatitis B.

Tyrosine Metabolism Pathway Is Downregulated in Dopaminergic Neurons with LRRK2 Overexpression in Drosophila

LRRK2 mutations are the leading cause of familial Parkinson's disease (PD) and are a significant risk factor for idiopathic PD cases. However, the molecular mechanisms underlying the degeneration of dopaminergic (DA) neurons in LRRK2 PD patients remain unclear. To determine the translatomic impact of LRRK2 expression in DA neurons, we employed gene set enrichment analysis (GSEA) to analyze a translating ribosome affinity purification (TRAP) RNA-seq dataset from a DA-neuron-specific-expressing Drosophila model. We found that the tyrosine metabolism pathway, including tyrosine hydroxylase (TH), is downregulated in DA neurons with LRRK2 overexpression; in contrast, the Hippo signaling pathway is downregulated in the G2019S mutant compared to wild-type LRRK2 in the DA neurons. These results imply that the downregulation of tyrosine metabolism occurs before pronounced DA neuron loss and that LRRK2 may downregulate the tyrosine metabolism in a DA-neuron-loss-independent way.

The Correlation between Metformin Use and Incident Dementia in Patients with New-Onset Diabetes Mellitus: A Population-Based Study

The evidence of metformin's effect on dementia is conflicting. This study investigates the association between metformin use and the risk of dementia among patients with diabetes mellitus (DM). This study included patients with new-onset DM between 2002 and 2013. We divided the patients into patients who used metformin and patients who did not. Two models were used to assess metformin use: the cumulative defined daily dose (cDDD) of metformin use and the intensity of metformin use. This study with 3-year and 5-year follow-ups investigated the risk of dementia among patients with DM who used metformin. At the 3-year follow-up, patients who received cDDD < 300 had an odds ratio (OR) of developing dementia of 0.92 (95% confidence interval [CI] = 0.89-0.96); patients who used metformin at intensities <10 and 10-25 DDD/month had ORs of 0.92 (95% CI: 0.87-0.97) and 0.92 (95% CI: 0.85-1.00), respectively. Metformin use at cDDD 300-500 (OR = 0.80, 95% CI = 0.56-1.15) or >500 (OR = 1.48, 95% CI = 0.48-4.60) or at an intensity >25 DDD/month (OR = 0.84, 95% CI = 0.60-1.18) were not associated with an incident of dementia. There were similar results at the 5-year follow-up. Patients with a low intensity of metformin use had a lower risk of dementia. However, higher doses of metformin with higher intensity exhibited no protective role in dementia. Prospective clinical trials are warranted to evaluate the actual underlying mechanisms between metformin dosage and the risk of dementia.