Tom1 (Target of Myb 1) Is a Novel Negative Regulator of Interleukin-1- and Tumor Necrosis Factor-Induced Signaling Pathways

Abstract

The Tom1 gene was initially identified as a specific target of retroviral oncogene v-Myb.1) This protein has an N-terminal VHS domain 2) followed by a short GAT domain.3) The crystal structures of the VHS domains of Tom1, 4) Hrs,5) and GGA proteins 6,7) have been determined. Although their global structures are similar, the VHS domains of GGA1 and GGA3, but not those of Tom1 and Hrs, have a specific recognition pocket for the mannose-6-phosphate receptor.6,7) Recently, the crystal structure of the GAT domain of GGA1 has been reported, [8][9][10] but its helical extension, which is indispensable for the association of GGA1 with ARF, is not conserved in the GAT domain of Tom1. Thus, the structurefunction relationships in the VHS and GAT domains of GGA proteins have been extensively elucidated, but those of Tom1 have not yet been determined. To investigate the function of Tom1, we previously carried out yeast two-hybrid screening using Tom1 as bait and found that Tollip is a Tom1-binding protein. 11)The adaptor protein Tollip was identified as an intermediate in IL-1-dependent signaling.12) IL-1 plays a central role in mediating a variety of inflammatory responses.13) The binding of IL-1 to the type I IL-1 receptor (IL-1RI) and the subsequent recruitment of the accessory protein IL-1RAcp result in their close spatial association, which allows the recruitment of the adaptor protein MyD88 and the IL-1R-associated-kinase (IRAK). In resting cells, Tollip forms a complex with IRAK and inhibits IL-1-induced signaling by blocking IRAK phosphorylation.12) In response to IL-1 signaling, IRAK becomes rapidly phosphorylated, dissociates from the receptor complex, and then associates with the downstream adaptor proteins such as TNF-associated factor 6 (TRAF6). The IL-1-induced signaling pathway bifurcates at TRAF6, 14,15) leading to the activation of the IkB kinase (IKK) complex and mitogen-activated protein kinases. These former and latter pathways are central to activation of the transcription factors nuclear factor (NF)-kB and AP-1, respectively. 16,17) In this study, we found that Tom1 inhibits the IL-1b-induced signaling pathway that leads to the activation of NFkB and AP-1, as Tollip does.12) On the other hand, in contrast to the action of Tollip, 12) Tom1 was found to inhibit the TNFa-induced signaling pathway, which also leads to the activation of NF-kB and AP-1. 18,19) To our knowledge, this is the first report of a common negative regulator of signaling pathways induced by IL-1b and TNF-a. MATERIALS AND METHODS Cell Culture and TransfectionHuman embryonic kidney (HEK) 293 cells were maintained in Dulbecco's modified Eagle's medium (DMEM) (Sigma) supplemented with 10% heat-inactivated fetal bovine serum (Invitrogen). Transfection was performed using FuGene6 (Roche) according to the manufacturer's protocol.Plasmid Construction The open-reading frames of mouse Tom1, Tollip, and IL-1RI, all containing EcoRI and SalI sites, were amplified by PCR using the respective primers. The PCR fragments were subcloned into the pGE...

miR-126 Is Downregulated in Cystic Fibrosis Airway Epithelial Cells and Regulates TOM1 Expression

“…We also observed miR-126 to be markedly increased in lung versus non-lung cell lines, consistent with other reports (6,22). Using bioinformatic tools, targets of miR-126 were identified and TOM1 was selected for experimental validation, given its known role in the innate immune response (17). Because of the consensus that a target predicted by a combination of algorithms may have more functional relevance than those predicted using a single algorithm alone, we analyzed a range of databases (23).…”

“…factors NF-kB and AP-1 (17). Our work builds on this by showing that TOM1 can also negatively regulate signaling to NF-kB induced by LPS via TLR4.…”

“…Moreover, this complex has been shown to traffic IL-1RI to the endosome for degradation (16). TOM1 has also been proposed as a negative regulator of IL-1b-and TNF-a-induced signaling pathways, whereby its overexpression can suppress the activity of the transcription factors NF-kB and AP-1 (17). In this study, we explore the presence of miRNA in CF for the first time.…”

Biomarkers of human oocyte developmental competence expressed in cumulus cells before ICSI: a preliminary study

“…Moreover, it inhibits some immune-like factors pathways including interleukins and the tumor necrosis factor-induced proteins. Other transcription factors like AP1 were also downregulated by TOM1 [88]. This transcription factor (AP1) is involved in the LH pathway of TNFAIP6 expression in the preovulatory bovine granulosa cells [89].…”

MicroRNAs and respiratory diseases

“…The authors suggest that TOM1 may play an antiinflammatory role in CF lung and postulate that its increased expression may be an attempt to compensate for the high proinflammatory burden in this condition. TOM1 acts as a negative regulator of signalling pathways induced by IL-1b and TNF-a and over-expression of TOM1 inhibits NF-kB activity [134].…”