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Increasing evidence has linked dysregulated interleukin (IL)-10 production by IL-10+ve B cells to autoimmunity, highlighting the importance of improving the understanding of the regulation of IL-10 production in these cells. In both B cells and myeloid cells, IL-10 can be produced in response to Toll-like receptor (TLR) agonists. In macrophages, previous studies have established that mitogen- and stress-activated protein kinases (MSKs) regulate IL-10 production via the phosphorylation of cAMP response element–binding (CREB) protein on the IL-10 promoter. We found here that although MSKs are activated in peritoneal B cells in response to TLR4 agonists, neither MSKs nor CREB are required for IL-10 production in these cells. Using a combination of chemical inhibitors and knockout mice, we found that IL-10 induction in B cells was regulated by an ERK1/2- and p90 ribosomal S6 kinase-dependent mechanism, unlike in macrophages in which p90 ribosomal S6 kinase was not required. This observation highlights fundamental differences in the signaling controlling IL-10 production in B cells and macrophages, even though these two cell types respond to a common TLR stimulus.

We have reported previously that activation of the MyD88-signaling network rapidly induces the formation of hybrid ubiquitin chains containing both Lys63-linked and Met1-linked ubiquitin (Ub) oligomers, some of which are attached covalently to Interleukin Receptor Associated kinase 1. Here we show that Lys63/Met1-Ub hybrids are also formed rapidly when the TNFR1/TRADD, TLR3/TRIF- and NOD1/RIP2-signaling networks are activated, some of which are attached covalently to Receptor-Interacting Protein 1 (TNFR1 pathway) or Receptor-Interacting Protein 2 (NOD1 pathway). These observations suggest that the formation of Lys63/Met1-Ub hybrids are of general significance for the regulation of innate immune signaling systems, and their potential roles in vivo are discussed. We also report that TNFα induces the attachment of Met1-linked Ub chains directly to TNF receptor 1, which do not seem to be attached covalently to Lys63-linked or other types of ubiquitin chain., Highlights • Ubiquitin chains containing both Lys63 and Met1 linkages are commonly formed during innate immune signaling. • Lys63/Met1-hybrid chains become attached to RIP1 and RIP2 in the TNFR1 and NOD1 signaling networks, respectively. • Potential advantages of Lys63/Met1-hybrids over separate ubiquitin chains are proposed. • Met1-linked ubiquitin is attached to TNFR1 without formation of a hybrid ubiquitin chain.

Summary AMPK is a sensor of cellular energy status and a promising target for drugs aimed at metabolic disorders. We have studied the selectivity and mechanism of a recently described activator, C2, and its cell-permeable prodrug, C13. C2 was a potent allosteric activator of α1-complexes that, like AMP, also protected against Thr172 dephosphorylation. Compared with AMP, C2 caused only partial allosteric activation of α2-complexes and failed to protect them against dephosphorylation. We show that both effects could be fully restored by exchanging part of the linker between the autoinhibitory and C-terminal domains in α2, containing the equivalent region from α1 thought to interact with AMP bound in site 3 of the γ subunit. Consistent with our results in cell-free assays, C13 potently inhibited lipid synthesis in hepatocytes from wild-type and was largely ineffective in AMPK-knockout hepatocytes; its effects were more severely affected by knockout of α1 than of α2, β1, or β2., Highlights • C2 activates AMPK via direct activation and protection against dephosphorylation • C2 and its cell-permeable prodrug C13 selectively activate AMPKα1 • A sequence located in the C-terminal alpha-linker of α1 confers specificity of C2 • C13 inhibits hepatic lipid synthesis via an AMPK-dependent and α1-selective mechanism, This study reports the selectivity and mechanism of a new AMPK activator. It inhibits hepatic lipid synthesis via an AMPKα1-isoform-selective mechanism and a sequence located in the C-terminal region of α1 that confers specificity.

The Vps34 Class III phosphoinositide 3-kinase (PI3K) phosphorylates phosphatidylinositol (PtdIns) at endosomal membranes to generate PtdIns(3)P that regulates membrane trafficking processes via its ability to recruit a subset of proteins possessing PtdIns(3)P-binding PX and FYVE domains. Here we describe a highly selective and potent inhibitor of Vps34, termed VPS34-IN1, that inhibits Vps34 with 25 nM IC50 in vitro but does not significantly inhibit the activity of 340 protein kinases or 25 lipid kinases tested that include all isoforms of Class I as well as Class II PI3K. Administration of VPS34-IN1 to cells, induces a rapid dose dependent dispersal of GFP-2xFYVEHrs , a specific PtdIns(3)P binding probe, from endosome membranes. Previous studies revealed that serum and glucocorticoid regulated kinase-3 (SGK3) possesses a PtdIns(3)P binding N-terminal PX domain. SGK3 was first identified as a novel isoform of SGK1 that played a role in enabling the IL-3-dependent survival of hematopoietic cells. We explored whether SGK3, the only protein kinase known to interact specifically with PtdIns(3)P, might be controlled by Vps34. We utilised U2OS Flp/In inducible cell line to find that the mutations disrupting PtdIns(3)P-binding, ablated SGK3 kinase activity by suppressing phosphorylation of the T-loop (PDK1 site) and hydrophobic motif (mTOR site) residues. Also, treatment of cells with VPS34-IN1 induced a rapid ∼50-60% loss of SGK3 phosphorylation and activity. Furthermore, a Class I PI3K inhibitor (GDC-0941) that does not inhibit Vps34, suppressed SGK3 activity by ∼30-40%. Combining VPS34-IN1 and GDC-0941 reduced SGK3 activity ∼80-90% similar to treatment with an mTOR inhibitor (AZD8055). This data suggest that SGK3 phosphorylation and hence activity is mainly controlled by the activity of PI3K Class I and Class III and the regulation of SGK3 activity through Vps34 may provide a prosurvival signal and a resistance mechanism during the treatment of cancer cells with PI3K Class I inhibitors. Citation Format: Ruzica Bago, Eeva Sommer, Nazma Malik, Michael J. Munson, Alan R. Prescott, Paul Davies, Shpiro Natalia, Ian G. Ganley, Dario R. Alessi. Characterization of VPS34-IN1, a specific inhibitor of Vps34 reveals that the phosphatidylinositol 3-phosphate binding SGK3 protein kinase is regulated by class III PI-3 kinase. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr A04.