TGF-ß1, but not bone morphogenetic proteins, activates Smad1/5 pathway in primary human macrophages and induces expression of proatherogenic genes.

Macrophages are responsible for the control of inflammation and healing, and their malfunction results in cardiometabolic disorders. TGF-ß is a pleiotropic growth factor with dual (protective and detrimental) roles in atherogenesis. We have previously shown that in human macrophages, TGF-ß1 activates Smad2/3 signaling and induces a complex gene expression program. However, activated genes were not limited to known Smad2/3-dependent ones, which prompted us to study TGF-ß1-induced signaling in macrophages in detail. Analysis of Id3 regulatory sequences revealed a novel enhancer, located between +4517 and 4662 bp, but the luciferase reporter assay demonstrated that this enhancer is not Smad2/3 dependent. Because Id3 expression is regulated by Smad1/5 in endothelial cells, we analyzed activation of Smad1/5 in macrophages. We demonstrate here for the first time, to our knowledge, that TGF-ß1, but not BMPs, activates Smad1/5 in macrophages. We show that an ALK5/ALK1 heterodimer is responsible for the induction of Smad1/5 signaling by TGF-ß1 in mature human macrophages. Activation of Smad1/5 by TGF-ß1 induces not only Id3, but also HAMP and PLAUR, which contribute to atherosclerotic plaque vulnerability. We suggest that the balance between Smad1/5- and Smad2/3-dependent signaling defines the outcome of the effect of TGF-ß on atherosclerosis where Smad1/5 is responsible for proatherogenic effects, whereas Smad2/3 regulate atheroprotective effects of TGF-ß.

Smurf2 regulates IL17RB by proteasomal degradation of its novel binding partner DAZAP2.

IL17RB is the receptor for IL17E, the only member of IL17 family promoting Th2 reactions. The mechanism of IL17BR regulation is poorly understood. We previously demonstrated that expression of IL17RB is induced on human macrophages by IL4 and enhanced by TGFß. In the present study we investigated the immediate signaling targets of IL17RB. Using Yeast Two Hybrid screening we identified DAZAP2 as a binding partner of IL17RB. We established that 2 SH2-binding domains of DAZAP2 are essential for its binding to IL17RB. Deletion of these domains or substitution of tyrosines to alanines abrogates the binding. In IL17RB DAZAP2-binding domain was mapped to the region between aa 329 and 347 within its cytoplasmic part. Confocal microscopy revealed that in primary human macrophages that do not express IL17RB DAZAP2 is predominantly localized in the nucleus, while in IL17RB positive macrophages a portion of DAZAP2 is visualized in the cytoplasm. Stimulation of IL17RB with its ligand IL17E induces accumulation of DAZAP2 in the cytoplasm. Further we established that DAZAP2 interacts with Smurf2 an E3 ubiquitin ligase which induces proteasome-dependent degradation of the protein. In summary we established a new mechanism of IL17RB regulation-Smurf2 dependent degradation of its adaptor protein DAZAP2.

Pro- and anti-inflammatory control of M-CSF-mediated macrophage differentiation.

Macrophages play a key role in inflammation, tissue regeneration and tolerance. Their differentiation is regulated by tissue cells derived CSF-1 (M-CSF). The ability of macrophages to use autocrine M-CSF to control their differentiation and function remained controversial. In this study we investigated the regulation of M-CSF production by Th1 and Th2 cytokines (IFN-γ and IL-4) and tolerogenic stimuli - glucocorticoid dexamethasone in primary human monocyte derived macrophages. We show that IFN-γ and IL-4 efficiently induce production of M-CSF while glucocorticoid inhibited it in a dose dependent manner. Since glucocorticoid inhibits production of inflammatory cytokines we tested whether this effect is a result of inhibited M-CSF production. We showed that exogenous M-CSF rescues the ability of glucocorticoid-treated macrophages to produce TNF and IL-6 in response to LPS. These data indicate that glucocorticoid-treated macrophages retain the ability to respond to M-CSF. Analyzing the mechanism of this responsiveness, we showed that dexamethasone up-regulates surface expression of M-CSF receptor - CSF-1R. We conclude that the ability of macrophages to produce M-CSF secures macrophage differentiation under Th1 and Th2 conditions if tissue cells are unable to supply enough M-CSF. Increased surface expression of CSF-1R in tolerogenic conditions guarantees response to minute amounts of exogenous M-CSF.