Serum deprivation/starvation leads to reactivation of HIV-1 in latently infected monocytes via activating ERK/JNK pathway

NG2/CSPG4 attenuates motility in mandibular fibrochondrocytes under serum starvation conditions

The migration of mandibular fibrochondrocytes is important for the development of the mandible, the homeostasis of the mandibular cartilage, and for the capacity of the tissue to respond to injury. Mandibular fibrochondrocytes have to overcome formidable obstacles during migration including a dense and heterogeneous three-dimensional matrix. Guiding the direction of cell migration and commitment to a migratory phenotype in this microenvironment necessitates a multivalent response to chemotactic and extracellular matrix-mediated stimuli. One of the key matrix components in the cartilage of the temporomandibular joint is type VI collagen. Neuron/glial antigen 2 (NG2/CSPG4) is a transmembrane proteoglycan that binds with collagen VI and has been implicated in a wide range of cell behaviors including cell migration, motility, adhesion, and proliferation. While NG2/CSPG4 has been shown to be a key regulator of mandibular cartilage homeostasis, its role in the migration of mandibular fibrochondrocytes during normal and cell stress conditions has yet to be resolved. Here, we address this gap in knowledge by characterizing NG2/CSPG4-dependent migration in mandibular fibrochondrocytes using primary mandibular fibrochondrocytes isolated from control and full length NG2/CSPG4 knockout mice, in primary mandibular fibrochondrocytes isolated from NG2|DsRed reporter mice and in an immortalized mandibular fibrochondrocyte cell line with a mutated NG2/CSPG4 ectodomain. All three cells demonstrate similar results, with loss of the full length or truncated NG2/CSPG4 increasing the rate of cell migration in serum starvation/cell stress conditions. These findings clearly implicate NG2/CSPG4 as a key molecule in the regulation of cell migration in mandibular fibrochondrocytes in normal and cell stress conditions, underscoring the role of NG2/CSPG4 as a mechanosensitive signaling hub in the mandibular cartilage.

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.

CounterAKTing HIV: Toward a “Block and Clear” Strategy?

The protein kinase B or Akt is a central regulator of survival, metabolism, growth and proliferation of the cells and is known to be targeted by various viral pathogens, including HIV-1. The central role of Akt makes it a critical player in HIV-1 pathogenesis, notably by affecting viral entry, latency and reactivation, cell survival, viral spread and immune response to the infection. Several HIV proteins activate the PI3K/Akt pathway, to fuel the progression of the infection. Targeting Akt could help control HIV-1 entry, viral latency/replication, cell survival of infected cells, HIV spread from cell-to-cell, and the immune microenvironment which could ultimately allow to curtail the size of the HIV reservoir. Beside the “shock and kill” and “block and lock” strategies, the use of Akt inhibitors in combination with latency inducing agents, could favor the clearance of infected cells and be part of new therapeutic strategies with the goal to “block and clear” HIV.

A novel biscoumarin derivative dephosphorylates ERK and alleviates apoptosis induced by mitochondrial oxidative damage in ischemic stroke mice

AIM

We previously reported the protective effects of biscoumarin derivatives against oxidative stress, but effects of the derivative on mitochondrial oxidative damage induced apoptosis in ischemic stroke remains unknown.

METHODS

Primary neurons were subjected to oxygen and glucose deprivation (OGD) for the in vitro simulation of ischemic stroke, and an ischemic stroke model was established in mice by operation of middle cerebral artery occlusion (MCAO).

RESULTS

The results indicated that the nontoxic concentration range of biscoumarin derivative Comp. B in neurons was from 0 to 30 μg/ml and the optimal protective concentration was 20 μg/ml. Treatment with Comp. B increased the cell survival rate and alleviated mitochondrial oxidative damage and apoptosis in OGD-treated neurons. Comp. B reduced the ratio of Bax/Bcl-2, inhibited the phosphorylation of ERK, and thus alleviated apoptosis in OGD-treated neurons. Further research demonstrated that the dephosphorylation effect on ERK of Comp. B is a key factor in alleviating apoptosis in neurons induced by OGD injury. Furthermore, Comp. B reduced the infarct volume, improved neurobehavioural score, and alleviated morphological changes and brain apoptosis in MCAO mice.

CONCLUSION

The novel biscoumarin derivative Comp. B alleviates mitochondrial oxidative damage and apoptosis in ischemic stroke mice. These findings might provide new insights that will aid in elucidating the effect of biscoumarin derivative against cerebral ischemic reperfusion injury and support the new development of Comp. B as a potential treatment for ischemic stroke.

Cadmium induces A549 cell migration and invasion by activating ERK

Cadmium (Cd) is an established carcinogen that is involved in the progression of lung cancer. However, the mechanisms underlying this Cd-induced process have yet to be fully elucidated. The present study explored the potential roles of phosphorylated (p)-ERK in the Cd-induced migration and invasion of lung cancer cells. An MTT assay was performed to evaluate cell viability whilst western blot analysis and reverse transcription-quantitative PCR were used to detect the expression of protein and mRNA, respectively. Migration and invasion assays were performed to assess cell migratory and invasive abilities. The results demonstrated that exposure to Cd increased the expression of p-ERK in A549 cells. Cd also enhanced the migration and invasion of A549 cells, which could be blocked via U0126 treatment (an inhibitor of mitogen activated protein kinase). In addition, it was identified that Cd-induced expression of matrix metalloproteinases 2 mRNA was mediated by p-ERK. In conclusion, the present findings indicated that Cd induced A549 cell migration and invasion by activating ERK, and it was hypothesized that p-ERK could serve as a target in the clinical treatment of Cd-induced lung cancer.