A TIR domain variant of MyD88 adapter-like (Mal)/TIRAP results in loss of MyD88 binding and reduced TLR2/TLR4 signaling

Division of Infectious Diseases and Immunology, Department of Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 07/2009; 284(38):25742-8. DOI: 10.1074/jbc.M109.014886
Source: PubMed


The adapter protein MyD88 adapter-like (Mal), encoded by TIR-domain containing adapter protein (Tirap) (MIM 606252), is the most polymorphic of the five adapter proteins involved in Toll-like receptor signaling, harboring eight non-synonymous single nucleotide polymorphisms in its coding region. We screened reported mutations of Mal for activity in reporter assays to test the hypothesis that variants of Mal existed with altered signaling potential. A TIR domain variant, Mal D96N (rs8177400), was found to be inactive. In reconstituted cell lines, Mal D96N acted as a hypomorphic mutation, with impaired cytokine production and NF-kappaB activation upon lipopolysaccharide or PAM2CSK4 stimulation. Moreover, co-immunoprecipitation studies revealed that Mal D96N is unable to interact with MyD88, a prerequisite for downstream signaling to occur. Computer modeling data suggested that residue 96 resides in the MyD88 binding site, further supporting these findings. Genotyping of Mal D96N in three different cohorts suggested that it is a rare mutation. We, thus, describe a rare variant in Mal that exerts its effect via its inability to bind MyD88.

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Available from: Theo S Plantinga, Apr 17, 2014
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    • "Therefore, it was proposed that PI(4,5)P2 recruits TIRAP to the plasma membrane following engagement of TLR4 ligand, thereby triggering the early phase of the MyD88-dependent pathway. In this working model, PI(4,5)P2-dependent TIRAP serves as a sorting adaptor for connecting TLR4 and MyD88, whereas MyD88 mainly functions as a signaling adaptor for TLR4 activation at the plasma membrane (52,53). A previous study demonstrated that Drosophila MyD88 harbors a PI(4,5)P2 binding motif at the C-terminus, which enables plasma membrane localization (54). "
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    • "To define the means by which TIRAP regulates TLR signaling from multiple organelles, we sought a cell type that would be easy to propagate and amenable to genetic manipulation. Immortalized BMDMs (iBMDMs) have emerged as a useful tool in this regard because they retain the signaling properties of their primary cell counterparts (Dixit et al., 2010; Halle et al., 2008), and TIRAP KO iBMDMs have been used to dissect the functions of this adaptor (Nagpal et al., 2009). Similar to our observations made in primary BMDMs, TIRAP was required for iBMDMs to respond to several substrains of HSV, including two that engage only TLR9 (Kos A and Kos CE) (Figure 2A) (Sato et al., 2006). "
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    • "co-immunoprecipitation studies and computer modeling data (Nagpal et al., 2009; George et al., 2010) revealed that this variation results in conformation changes in the MyD88 binding site and thus the TIRAP G286A variant is unable to interact with MyD88, a prerequisite for downstream signaling to activate the responses to Mtb. These facts lead us to suggest that the 286A allele is a risk factor for increased susceptibility to TB. "
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