Human APOBEC3B (A3B) has been described as a potent inhibitor of retroviral infection and retrotransposition. However, we found that the predominantly nuclear A3B only weakly restricted infection by HIV-1, HIV-1⌬vif, and human T-cell leukemia virus type 1 (HTLV-1), while significantly inhibiting LINE-1 retrotransposition. The chimeric construct A3G/B, in which the first 60 amino acids of A3B were replaced with those of A3G, restricted HIV-1, HIV-1⌬vif, and HTLV-1 infection, as well as LINE-1 retrotransposition. In contrast to the exclusively cytoplasmic A3G, which is inactive against LINE-1 retrotransposition, the A3G/B protein, while localized mainly to the cytoplasm, was also present in the nucleus. Further mutational analysis revealed that residues 18, 19, 22, and 24 in A3B were the major determinants for nuclear versus cytoplasmic localization and antiretroviral activity. HIV-1⌬vif packages A3G, A3B, and A3G/B into particles with close-to-equal efficiencies. Mutation E68Q or E255Q in the active centers of A3G/B resulted in loss of the inhibitory activity against HIV-1⌬vif, while not affecting activity against LINE-1 retrotransposition. The low inhibition of HIV1⌬vif by A3B correlated with a low rate of G-to-A hypermutation. In contrast, viruses that had been exposed to A3G/B showed a high number of G-to-A transitions. The mutation pattern was similar to that previously reported for A3B, with a preference for the GA context. In summary, these observations suggest that changing 4 residues in the amino terminus of A3B not only retargets the protein from the nucleus to the cytoplasm but also enhances its ability to restrict HIV while retaining inhibition of retrotransposition.

SUMMARY Transcriptional cyclin-dependent kinases play important roles in eukaryotic gene expression. CDK7, CDK9 (P-TEFb) and CDK13 are also critical for HIV replication. However, the function of CDK11 remained enigmatic. In this report, we determined that CDK11 regulates the cleavage and polyadenylation (CPA) of all viral transcripts. CDK11 was found associated with the TREX/THOC, which recruited this kinase to DNA. Once at the viral genome, CDK11 phosphorylated serines at position 2 in the CTD of RNAPII, which increased levels of CPA factors at the HIV 3’ end. In its absence, cleavage of viral transcripts was greatly attenuated. In contrast, higher levels of CDK11 increased the length of HIV polyA tails and the stability of mature viral transcripts. We conclude that CDK11 plays a critical role for the co-transcriptional processing of all HIV mRNA species.

The covalently closed circular DNA (cccDNA) of hepatitis B virus (HBV) is a viral center molecule for HBV infection and persistence. However, the cellular restriction factors of HBV cccDNA are not well understood. Here, we show that TGF-b can induce nuclear viral cccDNA degradation and hypermutation via activation-induced cytidine deaminase (AID) deamination activity in hepatocytes. This suppression by TGF-b is abrogated when AID or the activity of uracil-DNA glycosylase (UNG) is absent, which indicates that AID deamination and the UNG-mediated excision of uracil act in concert to degrade viral cccDNA. Moreover, the HBV core protein promotes the interaction between AID and viral cccDNA. Overall, our results indicate a novel molecular mechanism that allows cytokine TGF-b to restrict viral nuclear cccDNA in innate immunity, thereby suggesting a novel method for potentially eliminating cccDNA.Keywords: AID; cccDNA; HBV; Hypermutation; UNG Highlights • AID triggers HBV cccDNA degradation via its deamination activity.• AID induces viral cccDNA hypermutation.• TGF-b reduces viral cccDNA through AID in hepatocytes.Almost 350 million people who are chronically infected with hepatitis B virus (HBV) worldwide are at high risk of developing liver cirrhosis and hepatocellular carcinoma. Thus, HBV infection is a major global health concern [1-3]. The covalently closed circular DNA (cccDNA) of HBV plays an essential role in virus replication and persistence. After entry into the hepatocytes, HBV first forms cccDNA in the host cell's nucleus before transcribing viral RNAs, including a replicative RNA intermediate called pregenomic (pg) RNA that encodes two viral proteins, HBV core (HBc), and HBV polymerase (Pol), which encapsidate pgRNA to form a nucleocapsid. HBV Pol reverse transcribes pgRNA to produce relaxed circular DNA

One approach to improving the activity of anticancer drugs is to bind them to the human α-fetoprotein (HAFP) that recognizes the tumor-associated cell-surface HAFP receptor. A drug can be bound to the HAFP by covalent conjugation or within a non-covalent complex. Specially designed linkers couple cytotoxins to the HAFP and ensure the stability of the HAFP-drug conjugate in the circulation and the activation of the drug in the cancer cell. On the other hand, AFP-drug non-covalent complexes can exploit the natural role of the AFP as a nutrition delivery "shuttle". In this article we review the design of HAFP-drug conjugates and AFP-drug complexes and their potential uses.

No Abstract