Biology subjects

Lichauco, K.

Publications and source records attributed to Lichauco, K..

3 recordsLinked to original sources

bioRxiv2024

RIPK3 coordinates RHIM domain-dependent inflammatory transcription in neurons

Neurons are post-mitotic, non-regenerative cells that have evolved fine-tuned immunological responses to maintain life-long cellular integrity; this includes resistance to common programmed cell death (PCD) pathways, including apoptosis and necroptosis. We have previously demonstrated a necroptosis-independent role for the key necroptotic kinase RIPK3 in host defense against neurotropic flavivirus infection. While this work showed that neuronal RIPK3 expression is essential for chemokine production and recruitment of peripheral immune cells to the infected CNS, the full RIPK3-dependent transcriptional signature, and the molecular mechanism underlying RIPK3-dependent transcription in neurons are incompletely understood. It also remains unclear what factors govern differential RIPK3 effector functions in different cell types. Here, we show that RIPK3 activation has distinct outcomes in primary cortical neurons when compared to mouse embryonic fibroblasts (MEFs) during Zika virus (ZIKV) infection or following sterile activation. We found that RIPK3 activation does not induce death in neurons; in these cells, RIPK3 is the dominant driver of antiviral gene transcription following ZIKV infection. While RIPK3 activation in MEF cells induces cell death, ablation of downstream cell death effectors unveils a RIPK3-dependent transcriptional program which largely overlaps with that observed in ZIKV-infected neurons. Using death resistant MEFs as a model to study RIPK3 signaling revealed that RIPK3 transcription relied on interactions with the RHIM domain-containing proteins RIPK1 and TRIF, effects mirrored in the RIPK3-dependent antiviral transcriptional signature observed in ZIKV-infected neurons. These findings suggest the pleotropic functions of RIPK3 are largely context dependent and that in cells that are resistant to cell death, RIPK3 acts as a mediator of inflammatory transcription. One Sentence SummaryRHIM-domain containing proteins form a conserved signaling network capable of mediating inflammatory transcription and cell death.

immunology↗

bioRxiv2023

The CD4 transmembrane GGXXG and juxtamembrane (C/F)CV+C motifs mediate pMHCII-specific signaling independently of CD4-Lck interactions

CD4+ T cell activation is driven by 5-module receptor complexes. The T cell receptor (TCR) is the receptor module that binds composite surfaces of peptide antigens embedded within MHCII molecules (pMHCII). It associates with three signaling modules (CD3{gamma}{varepsilon}, CD3{delta}{varepsilon}, and CD3{zeta}{zeta}) to form TCR-CD3 complexes. CD4 is the coreceptor module. It reciprocally associates with TCR-CD3-pMHCII assemblies on the outside of a CD4+ T cells and with the Src kinase, LCK, on the inside. Previously, we reported that the CD4 transmembrane GGXXG and cytoplasmic juxtamembrane (C/F)CV+C motifs found in eutherian (placental mammal) CD4 have constituent residues that evolved under purifying selection (Lee, et al., 2022). Expressing mutants of these motifs together in T cell hybridomas increased CD4-LCK association but reduced CD3{zeta}, ZAP70, and PLC{gamma}1 phosphorylation levels, as well as IL-2 production, in response to agonist pMHCII. Because these mutants preferentially localized CD4-LCK pairs to non-raft membrane fractions, one explanation for our results was that they impaired proximal signaling by sequestering LCK away from TCR-CD3. An alternative hypothesis is that the mutations directly impacted signaling because the motifs normally play an LCK-independent role in signaling. The goal of this study was to discriminate between these possibilities. Using T cell hybridomas, our results indicate that: intracellular CD4-LCK interactions are not necessary for pMHCII-specific signal initiation; the GGXXG and (C/F)CV+C motifs are key determinants of CD4-mediated pMHCII-specific signal amplification; the GGXXG and (C/F)CV+C motifs exert their functions independently of direct CD4-LCK association. These data provide a mechanistic explanation for why residues within these motifs are under purifying selection in jawed vertebrates. The results are also important to consider for biomimetic engineering of synthetic receptors.

immunology↗

bioRxiv2021

Enhancing and inhibitory motifs have coevolved to regulate CD4 activity

CD4+ T cells use T cell receptor (TCR)-CD3 complexes, and CD4, to respond to peptide antigens within MHCII molecules (pMHCII). We report here that, through [~]435 million years of evolution in jawed vertebrates, purifying selection has shaped motifs in the extracellular, transmembrane, and intracellular domains of eutherian CD4 that both enhance pMHCII responses and are coevolving with residues in an intracellular motif that inhibits pMHCII responses. Importantly, while CD4 interactions with the Src kinase, Lck, are classically viewed as the key determinant of CD4s contribution to pMHCII responses, we found that without the inhibitory motif CD4-Lck interactions are not necessary for robust responses to pMHCII. In summary, motifs that mediate events on the outside and inside of CD4+ T cells coevolved to finetune the relay of pMHCII-specific information across the membrane. These results have implications for the evolution and function of complex transmembrane receptors and for biomimetic engineering.

immunology↗