Biology subjects

Choi, S.

Publications and source records attributed to Choi, S..

5 recordsLinked to original sources

bioRxiv2018

Quantitative Real-Time Imaging of Glutathione with Sub-Cellular Resolution

Quantitative imaging of glutathione with high spatial and temporal resolution is essential for studying the roles of glutathione in redox biology. We developed a fluorescent glutathione probe--HaloRT--that targets organelles of interest through expressing organelle-specific HaloTag proteins. Using HaloRT, we quantitatively measure the glutathione concentrations in the nucleus and the cytosol and find no appreciable concentration gradient between these two organelles, challenging the view of nuclear compartmentalization of glutathione.

cell biology↗

bioRxiv2018

Pseudomonas syringae evades phagocytosis in animal cells through type III effector-mediated inhibition of the LIM kinase-cofilin system

Certain animal and plant pathogenic bacteria have developed virulence factors (including effector proteins) that enable them to overcome host immunity. A plant pathogen, Pseudomonas syringae pv. tomato (Pto), secretes a large repertoire of effectors into plant cells via a type III secretory apparatus, thereby suppressing plant immunity. Here, we show that exposure to Pto caused sepsis in mice. Surprisingly, the effector HopQ1 disrupted phagocytosis by inhibiting actin rearrangement via a direct interaction with the LIM domain of the animal target protein LIM kinase, a key regulator of actin polymerization. The results provide new insights into cross-kingdom pathogenicity of bacteria. The current studies demonstrate that certain plant pathogenic bacteria such as Pto can be fatal in animals due to cross-kingdom host immune suppression.

microbiology↗

bioRxiv2018

The C. elegans heterochronic gene lin-28 coordinates the timing of hypodermal and somatic gonadal programs for hermaphrodite reproductive system morphogenesis

C. elegans heterochronic genes determine the timing of expression of specific cell fates in particular stages of developing larva. However, their broader roles in coordinating developmental events across diverse tissues has been less well investigated. Here, we show that loss of lin-28, a central heterochronic regulator of hypodermal development, causes reduced fertility associated with abnormal somatic gonad morphology. In particular, the abnormal spermatheca-uterine valve morphology of lin-28(lf) hermaphrodites trap embryos in the spermatheca, which disrupts ovulation and causes embryonic lethality. The same genes that act downstream of lin-28 in the regulation of hypodermal developmental timing also act downstream of lin-28 in somatic gonad morphogenesis and fertility. Importantly, we find that hypodermal expression, but not somatic gonadal expression, of lin-28 is sufficient for restoring normal somatic gonad morphology in lin-28(lf) mutants. We propose that the abnormal somatic gonad morphogenesis of lin-28(lf) hermaphrodites results from temporal discoordination between the accelerated hypodermal development and normally timed somatic gonad development. Thus, our findings exemplify how a cell-intrinsic developmental timing program can also control cell non-autonomous signaling critical for proper development of other interacting tissues.

developmental biology↗

bioRxiv2018

The Specificity of IQGAP1 Toward the PI3K-Akt Pathway is Dependent on the IQ3 motif

Epidermal growth factor receptor (EGFR) and its downstream phosphatidylinositol 3-kinase (PI3K) pathway are commonly deregulated in many cancers including head and neck cancer (HNC). Recently, we have shown that the IQ motif-containing GTPase-activating protein 1 (IQGAP1) provides a molecular platform to scaffold all the components from the PI3K-Akt pathway and results in the sequential generation of phosphatidylinositol-3,4,5-triphosphate (PI3,4,5P3). This makes the IQGAP1-PI3K scaffold a promising therapeutic target. In addition to the PI3K-Akt pathway, IQGAP1 also scaffolds the Ras-ERK pathway. To identify an IQGAP1 mutant that specifically loses IQGAP1-PI3K signaling but not other functions, we have focused on the IQ3 motif since this region binds with both the PIPK1 and PI3K enzymes and a short peptide derived from this sequence blocks binding and PI3K signaling. An IQ3 deletion mutant ({Delta}IQ3) in IQGAP1 was functionally compared with wild-type (WT) IQGAP1. We found that the IQ3 domain specifically mediates the PI3K-Akt pathway but does not regulate the Ras-ERK pathway. The IQ3 deletion mutant lost interactions with PI3K-Akt components but retained its binding of ERK pathway components and cell surface receptors, EGFR and integrins. In addition, the IQ3 deletion mutant lost regulation of cell migration. Consistently, the IQ3 motif derived peptide blocked Akt activation and led to the blockage of invasion mediated by EGFR organized into an integrin complex by syndecan-4. Taken together, this work has defined the IQGAP1 IQ3 motif as a specific target sequence for the scaffolding of the PI3K-AKT pathway.

cell biology↗

bioRxiv2018

Role of IQGAP1 in Head and Neck Carcinogenesis

Head and neck squamous cell carcinoma (HNSCC) is a common cancer in humans. Phosphoinositide 3-kinase (PI3K)/AKT signaling, along with its downstream effector mTOR, is one of the most frequently altered pathways in HNSCC, and is downstream of growth factor signaling including that mediated by epidermal growth factor receptor (EGFR), which is also commonly upregulated in HNSCC. Recently, IQ motif-containing GTPase activation protein 1 (IQGAP1) has been reported to function as a scaffold for the enzymes involved in the PI3K/AKT signaling pathway. Iqgap1 gene expression is increased in human HNSCCs, raising the hypothesis that it acts as an oncogene in this cancer. Whether IQGAP1 is necessary for HNSCC development as well as what is its underlying mechanism are both unknown. Here we report on the role of IQGAP1 in HNSCC by performing a combination of in vitro studies using human cancer cell lines, and in vivo studies using a well-validated preclinical mouse model for HNSCC that is known to depend upon EGFR signaling. Cells knocked out for IQGAP1 lost AKT signaling. Disruption of IQGAP1-scaffolded PI3K/AKT signaling using a peptide that interferes with the ability of IQGAP1 to bind to PI3K reduced HNSCC cell survival. In vivo studies utilizing Iqgap1-null (Iqgap1-/-) mice demonstrated that IQGAP1 is necessary for efficient PI3K signaling upon EGF-stimulation. Treatment of Iqgap1-/- mice with the oral carcinogen, 4-nitroquinoline 1-oxide (4NQO), Iqgap1-/- led to significantly lower multiplicities of cancer foci as well as significantly lower numbers of high grade cancers than observed in similarly treated Iqgap1+/+ mice. IQGAP1 protein was increased in its expression in HNSCCs arising in the Iqgap1+/+ mice, consistent with that seen in human HNSCCs. We also observed a significant down-regulation of PI3K signaling in 4NQO-induced HNSCCs arising in the Iqgap1-/- mice, consistent with IQGAP1 contributing to carcinogenesis by promoting PI3K signaling. Our studies, therefore, support the hypothesis that IQGAP1 acts as an oncogene in head and neck carcinogenesis, and provide mechanistic insight into its role.

cancer biology↗