[Transcriptional Modification and Potential Intracellular Signaling Mechanisms in Human Macrophages Primed by Interferon-γ].

OBJECTIVE: To explore the transcriptional gene expression profile up-regulated in human macrophages stimulated by interferon-γ (IFN-γ) and the underlying intracellular signaling mechanisms. METHODS: RNA-seq was used to sequence and compare the differential gene expression profiles of human macrophage cell line U937 before and after IFN-γ stimulation, and the significantly up-regulated genes were screened out, which were verified by fluorescence-based real-time quantitative polymerase chain reaction (qPCR) in U937 and THP1 cell lines, respectively. JAK/STAT, MAPK/ERK and PI3K/AKT pathway inhibitors were added to simultaneously to the cultured U937 cells upon IFN-γ priming to detect their effects on the expressions of the up-regulated genes to explore the key regulatory mechanisms. RESULTS: RNA-seq and qPCR results showed that, the well-recognized chemokines CXCL9, CXCL10 and CXCL11, the APOL family including APOL1, APOL2, APOL3, APOL4, APOL6 and GBP family GBP1, GBP2, GBP3, GBP4 and GBP5 as well were significantly up-regulated in IFN-γ-stimulated U937 cells. JAK/STAT3 pathway inhibitor inhibited the upregulation of APOL1, APOL4, GBP1, GBP4 and GBP5 genes induced by IFN-γ, while MAPK/ERK pathway inhibitor inhibited the upregulation of CXCL10 gene. PI3K/AKT pathway inhibitor inhibited the upregulation of APOL1,APOL4, APOL6, GBP1 and GBP5 genes induced by IFN-γ, all three signal pathway inhibitors could inhibit the upregulation of CXCL9 gene, and none of them could inhibit the upregulation of APOL3 gene. CONCLUSION: Upon IFN-γ stimulation, some family molecules of APOL and GBP in macrophages are significantly up-regulated, and PI3K/AKT, JAK/STAT3 and MAPK/ERK pathways have positive regulation on their expressions, respectively.

Decoding the network of Trypanosoma brucei proteins that determines sensitivity to apolipoprotein-L1.

In contrast to Trypanosoma brucei gambiense and T. b. rhodesiense (the causative agents of human African trypanosomiasis), T. b. brucei is lysed by apolipoprotein-L1 (apoL1)-containing human serum trypanolytic factors (TLF), rendering it non-infectious to humans. While the mechanisms of TLF1 uptake, apoL1 membrane integration, and T. b. gambiense and T. b. rhodesiense apoL1-resistance have been extensively characterised, our understanding of the range of factors that drive apoL1 action in T. b. brucei is limited. Selecting our bloodstream-form T. b. brucei RNAi library with recombinant apoL1 identified an array of factors that supports the trypanocidal action of apoL1, including six putative ubiquitin modifiers and several proteins putatively involved in membrane trafficking; we also identified the known apoL1 sensitivity determinants, TbKIFC1 and the V-ATPase. Most prominent amongst the novel apoL1 sensitivity determinants was a putative ubiquitin ligase. Intriguingly, while loss of this ubiquitin ligase reduces parasite sensitivity to apoL1, its loss enhances parasite sensitivity to TLF1-dominated normal human serum, indicating that free and TLF1-bound apoL1 have contrasting modes-of-action. Indeed, loss of the known human serum sensitivity determinants, p67 (lysosomal associated membrane protein) and the cathepsin-L regulator, 'inhibitor of cysteine peptidase', had no effect on sensitivity to free apoL1. Our findings highlight a complex network of proteins that influences apoL1 action, with implications for our understanding of the anti-trypanosomal action of human serum.

Apolipoprotein L1 confers pH-switchable ion permeability to phospholipid vesicles.

Apolipoprotein L1 (ApoL1) is a human serum protein conferring resistance to African trypanosomes, and certain ApoL1 variants increase susceptibility to some progressive kidney diseases. ApoL1 has been hypothesized to function like a pore-forming colicin and has been reported to have permeability effects on both intracellular and plasma membranes. Here, to gain insight into how ApoL1 may function in vivo, we used vesicle-based ion permeability, direct membrane association, and intrinsic fluorescence to study the activities of purified recombinant ApoL1. We found that ApoL1 confers chloride-selective permeability to preformed phospholipid vesicles and that this selectivity is strongly pH-sensitive, with maximal activity at pH 5 and little activity above pH 7. When ApoL1 and lipid were allowed to interact at low pH and were then brought to neutral pH, chloride permeability was suppressed, and potassium permeability was activated. Both chloride and potassium permeability linearly correlated with the mass of ApoL1 in the reaction mixture, and both exhibited lipid selectivity, requiring the presence of negatively charged lipids for activity. Potassium, but not chloride, permease activity required the presence of calcium ions in both the association and activation steps. Direct assessment of ApoL1-lipid associations confirmed that ApoL1 stably associates with phospholipid vesicles, requiring low pH and the presence of negatively charged phospholipids for maximal binding. Intrinsic fluorescence of ApoL1 supported the presence of a significant structural transition when ApoL1 is mixed with lipids at low pH. This pH-switchable ion-selective permeability may explain the different effects of ApoL1 reported in intracellular and plasma membrane environments.

APOLs with low pH dependence can kill all African trypanosomes.

The primate-specific serum protein apolipoprotein L1 (APOL1) is the only secreted member of a family of cell death promoting proteins 1-4 . APOL1 kills the bloodstream parasite Trypanosoma brucei brucei, but not the human sleeping sickness agents T.b. rhodesiense and T.b. gambiense 3 . We considered the possibility that intracellular members of the APOL1 family, against which extracellular trypanosomes could not have evolved resistance, could kill pathogenic T. brucei subspecies. Here we show that recombinant APOL3 (rAPOL3) kills all African trypanosomes, including T.b. rhodesiense, T.b. gambiense and the animal pathogens Trypanosoma evansi, Trypanosoma congolense and Trypanosoma vivax. However, rAPOL3 did not kill more distant trypanosomes such as Trypanosoma theileri or Trypanosoma cruzi. This trypanolytic potential was partially shared by rAPOL1 from Papio papio (rPpAPOL1). The differential killing ability of rAPOL3 and rAPOL1 was associated with a distinct dependence on acidic pH for activity. Due both to its instability and toxicity when injected into mice, rAPOL3 cannot be used for the treatment of infection, but an experimental rPpAPOL1 mutant inspired by APOL3 exhibited enhanced trypanolytic activity in vitro and the ability to completely inhibit T.b. gambiense infection in mice. We conclude that pH dependence influences the trypanolytic potential of rAPOLs.