STUB1/CHIP promotes ubiquitination and degradation of HIV-1 Vif to restore the cellular level of APOBEC3G protein

VEZF1, destabilized by STUB1, affects cellular growth and metastasis of hepatocellular carcinoma by transcriptionally regulating PAQR4

Hepatocellular carcinoma (HCC) is an aggressive solid malignancy, and recurrence and metastasis are major incentives contributing to its poor outcome. Vascular endothelial zinc finger 1 (VEZF1) has been recognized as an oncoprotein in certain types of cancer, but the expression pattern and regulatory mechanism in HCC remains unclear. This study focused on the functional effect and regulatory basis of VEZF1 in HCC. Microarray analysis identified the differentially expressed VEZF1 in HCC, and we validated its raised expression in HCC clinical samples. Artificial modulation of VEZF1 (knockdown and overexpression) was conducted to explore its role in HCC progression both in vitro and in vivo. It was shown that silencing of VEZF1 suppressed, whereas its overexpression promoted HCC cellular proliferation and metastasis abilities. Mechanistically, VEZF1 transcriptionally activated progestin and adipoQ receptor 4 (PAQR4) to accelerate HCC progression. Furthermore, VEZF1 is confirmed as a substrate of stress-inducible phosphoprotein 1 homology and U-box containing protein 1 (STUB1), and its stability is impacted by STUB1-mediated ubiquitination degradation. Conjointly, our work suggested that VEZF1, destabilized by STUB1, participates in HCC progression by regulating PAQR4. The STUB1/VEZF1/PAQR4 mechanism might provide novel insights on guiding early diagnosis and therapy in HCC patients.

A CRISPR-Cas Cure for HIV/AIDS

Human immunodeficiency virus (HIV) infections and HIV-induced acquired immunodeficiency syndrome (AIDS) continue to represent a global health burden. There is currently no effective vaccine, nor any cure, for HIV infections; existing antiretroviral therapy can suppress viral replication, but only as long as antiviral drugs are taken. HIV infects cells of the host immune system, and it can establish a long-lived viral reservoir, which can be targeted and edited through gene therapy. Gene editing platforms based on the clustered regularly interspaced palindromic repeat-Cas system (CRISPR-Cas) have been recognized as promising tools in the development of gene therapies for HIV infections. In this review, we evaluate the current landscape of CRISPR-Cas-based therapies against HIV, with an emphasis on the infection biology of the virus as well as the activity of host restriction factors. We discuss the potential of a combined CRISPR-Cas approach that targets host and viral genes to activate antiviral host factors and inhibit viral replication simultaneously. Lastly, we focus on the challenges and potential solutions of CRISPR-Cas gene editing approaches in achieving an HIV cure.

Host AKT-mediated phosphorylation of HIV-1 accessory protein Vif potentiates infectivity via enhanced degradation of the restriction factor APOBEC3G

HIV-1 encodes accessory proteins that neutralize antiviral restriction factors to ensure its successful replication. One accessory protein, the HIV-1 viral infectivity factor (Vif), is known to promote ubiquitination and proteasomal degradation of the antiviral restriction factor apolipoprotein B mRNA-editing enzyme-catalytic polypeptide-like 3G (APOBEC3G), a cytosine deaminase that leads to hypermutations in the viral DNA and subsequent aberrant viral replication. We have previously demonstrated that the HIV-1 viral transcription mediator Tat activates the host progrowth PI-3–AKT pathway, which in turn promotes HIV-1 replication. Because the HIV-1 Vif protein contains the putative AKT phosphorylation motif RMRINT, here we investigated whether AKT directly phosphorylates HIV-1 Vif to regulate its function. Coimmunoprecipitation experiments showed that AKT and Vif interact with each other, supporting this hypothesis. Using in vitro kinase assays, we further showed that AKT phosphorylates Vif at threonine 20, which promotes its stability, as Vif becomes destabilized after this residue is mutated to alanine. Moreover, expression of dominant-negative kinase-deficient AKT as well as treatment with a chemical inhibitor of AKT increased K48-ubiquitination and proteasomal degradation of HIV-1 Vif. In contrast, constitutively active AKT (Myr-AKT) reduced K48-ubiquitination of Vif to promote its stability. Finally, inhibition of AKT function restored APOBEC3G levels, which subsequently reduced HIV-1 infectivity. Thus, our results establish a novel mechanism of HIV-1 Vif stabilization through AKT-mediated phosphorylation at threonine 20, which reduces APOBEC3G levels and potentiates HIV-1 infectivity.