Activation of TAK1 by Sef-S induces apoptosis in 293T cells

Interleukin-17 Receptor D in Physiology, Inflammation and Cancer

Interleukin-17 receptor D (IL-17RD) is an evolutionarily conserved member of the IL-17 receptor family. Originally identified as a negative regulator of fibroblast growth factor (FGF) signaling under the name of Sef (Similar expression to FGF genes), IL-17RD was subsequently reported to regulate other receptor tyrosine kinase signaling pathways. In addition, recent studies have shown that IL-17RD also modulates IL-17 and Toll-like receptor (TLR) signaling. Combined genetic and cell biology studies have implicated IL-17RD in the control of cell proliferation and differentiation, cell survival, lineage specification, and inflammation. Accumulating evidence also suggest a role for IL-17RD in tumorigenesis. Expression of IL-17RD is down-regulated in various human cancers and recent work has shown that loss of IL-17RD promotes tumor formation in mice. However, the exact mechanisms underlying the tumor suppressor function of IL-17RD remain unclear and some studies have proposed that IL-17RD may exert pro-tumorigenic effects in certain contexts. Here, we provide an overview of the signaling functions of IL-17RD and review the evidence for its involvement in cancer.

Interleukin-17 receptor D (Sef) is a multi-functional regulator of cell signaling

Interleukin-17 receptor D (IL17RD or IL-17RD) also known as Sef (similar expression to fibroblast growth factor), is a single pass transmembrane protein that is reported to regulate several signaling pathways . IL17RD was initially described as a feedback inhibitor of fibroblast growth factor (FGF) signaling during zebrafish and frog development. It was subsequently determined to regulate other receptor tyrosine kinase signaling cascades as well as several proinflammatory signaling pathways including Interleukin-17A (IL17A), Toll-like receptors (TLR) and Interleukin-1α (IL1α) in several vertebrate species including humans. This review will provide an overview of IL17RD regulation of signaling pathways and functions with emphasis on regulation of development and pathobiological conditions. We will also discuss gaps in our knowledge about IL17RD function to provide insight into opportunities for future investigation. Video Abstract.

Paclitaxel induces apoptosis through the TAK1-JNK activation pathway

Paclitaxel (PTX) has previously been used to treat tumours of various tissue origins, such as lung, breast, ovarian, prostate cancers and leukemia. PTX‐induced apoptosis is associated with p38 mitogen‐activated protein kinase (p38 MAPK), extracellular signal‐regulated kinase (ERK), nuclear factor‐kappa B (NF‐κB) and c‐Jun N‐terminal kinase or stress‐activated protein kinase (JNK/ SAPK) pathways. Transforming growth factor‐beta‐activated kinase 1 (TAK1) and TAK1‐binding protein 1 (TAB1) play an important role in cell apoptosis through the p38, ERK, NF‐κB and JNK signal transduction pathways. To investigate the role of TAK1 in PTX‐induced cell apoptosis, we treated HEK293 and 8305C cells with 0–20 µm PTX for 6, 12 or 24 h. To investigate whether TAK1 can cooperate with PTX for cancer treatment, we transfected cells with TAK1, TAB1 or control plasmid and treated them with PTX (3–10 µm) for 9–24 h. Apoptosis rates were analysed by flow cytometry (Annexin V/PI). Endogenous TAK1 and TAB1, caspase‐7 cleavage, poly ADP‐ribose polymerase (PARP) cleavage, Bcl‐xL level, phospho‐p44/42, phospho‐JNK and phospho‐p38 were detected by western blot. We show that in HEK293 and 8305C cells, PTX enhanced the endogenous TAK1/TAB1 level and induced cell apoptosis in a dose‐ and time‐dependent manner. Upon TAK1 overexpression in HEK293 cells treated with PTX, apoptosis rate, JNK phosphorylation and PARP cleavage increased contrary to heat‐shocked or untreated cells. CRISPR editing of the tak1 gene upon PTX treatment resulted in lower phospho‐JNK and PARP cleavage levels than in cells transfected with the control or the TAK1‐ or TAB1 + TAK1‐containing plasmids. TAK1‐K63A could not induce JNK phosphorylation or PARP cleavage. We conclude that PTX induces HEK293 and 8305C cell apoptosis through the TAK1–JNK activation pathway, potentially highlighting TAK1’s role in chemosensitivity.

Post-Translational Modifications of the TAK1-TAB Complex

Transforming growth factor-β (TGF-β)-activated kinase 1 (TAK1) is a member of the mitogen-activated protein kinase kinase kinase (MAPKKK) family that is activated by growth factors and cytokines such as TGF-β, IL-1β, and TNF-α, and mediates a wide range of biological processes through activation of the nuclear factor-κB (NF-κB) and the mitogen-activated protein (MAP) kinase signaling pathways. It is well established that activation status of TAK1 is tightly regulated by forming a complex with its binding partners, TAK1-binding proteins (TAB1, TAB2, and TAB3). Interestingly, recent evidence indicates the importance of post-translational modifications (PTMs) of TAK1 and TABs in the regulation of TAK1 activation. To date, a number of PTMs of TAK1 and TABs have been revealed, and these PTMs appear to fine-tune and coordinate TAK1 activities depending on the cellular context. This review therefore focuses on recent advances in the understanding of the PTMs of the TAK1-TAB complex.

Orphan receptor IL-17RD regulates Toll-like receptor signalling via SEFIR/TIR interactions

Receptor families of the innate immune response engage in 'cross-talk' to tailor optimal immune responses against invading pathogens. However, these responses are subject to multiple levels of regulation to keep in check aberrant inflammatory signals. Here, we describe a role for the orphan receptor interleukin-17 receptor D (IL-17RD) in negatively regulating Toll-like receptor (TLR)-induced responses. Deficiency of IL-17RD expression in cells leads to enhanced pro-inflammatory signalling and gene expression in response to TLR stimulation, and Il17rd(-/-) mice are more susceptible to TLR-induced septic shock. We demonstrate that the intracellular Sef/IL-17R (SEFIR) domain of IL-17RD targets TIR adaptor proteins to inhibit TLR downstream signalling thus revealing a paradigm involving cross-regulation of members of the IL-17R and TLR families.

Characterization of Golgi scaffold proteins and their roles in compartmentalizing cell signaling

Subcellular compartmentalization has become an important theme in cell signaling. In particular, the Golgi apparatus (GA) plays a prominent role in compartmentalizing signaling cascades that originate at the plasma membrane or other organelles. To precisely regulate this process, cells have evolved a unique class of organizer proteins, termed "scaffold proteins". Sef, PAQR3, PAQR10 and PAQR11 are scaffold proteins that have recently been identified on the GA and are referred to as Golgi scaffolds. The major cell growth signaling pathways, such as Ras/MAPK, PI3K/AKT, insulin and VEGF (vascular endothelial growth factor), are tightly regulated spatially and temporally by these Golgi scaffolds to ensure a physiologically appropriate outcome. Here, we discuss the subcellular localization and characterization of the topology and functional domains of these Golgi scaffolds and summarize their roles in the compartmentalization of cell signaling. We also highlight the physiological and pathological roles of these Golgi scaffolds in tumorigenesis and developmental disorders.