Threonine 680 phosphorylation of FLJ00018/PLEKHG2, a Rho family-specific guanine nucleotide exchange factor, by epidermal growth factor receptor signaling regulates cell morphology of Neuro-2a cells

PLEKHG2 Promotes NSCLC Cell Growth by Increasing Glycolysis via Activated PI3K/AKT Pathway

Purpose: PLEKHG2 is a member of the diffuse B-cell lymphoma family. The function of PLEKHG2 in NSCLC was still unclear. This study aimed to investigate the relationship between the upregulated expression of PLEKHG2 and the prognosis of NSCLC and to revealed its mechanisms. Materials and methods: The expression of PLEKHG2 in NSCLC patients and its relationship with prognosis were first determined by analyzing public databases. Validation was performed in NSCLC cell lines and patient`s tumor tissues. PLEKHG2-silenced H1299 cells and PLEKHG2 overexpressing PC9 cells were constructed and used to validate its function. Glycolysis was evaluated by assaying cellular metabolites, glucose uptake and the expression levels of biomarkers of glycolysis. The relationship of PLEKHG2 and the PI3K/Akt pathway was demonstrated by small molecule inhibitors. The function of PLEKHG2 was evaluated in vivo by a H1299 cell derived xenograft (CDX) model. Results: PLEKEHG2 was highly expressed in NSCLC tissues and associated with poor prognosis. In PLEKHG2 knockdown H1299 cells, ATP and lactate production and glucose uptake were significantly inhibited. The opposite results were observed in PC9 cells with PLEKHG2 overexpression. The increased glycolysis following PLEKHG2 overexpression was abolished by adding the PI3K/AKT pathway inhibitor LY294002, suggesting that PLEKHG2 promotes glycolysis in NSCLC cells via activation of the PI3K/AKT pathway. Finally, we found that PLEKHG2 knockdown inhibited the tumor growth in the H1299 CDX model. Conclusion: PLEKHG2 contributed to NSCLC development by promoting glycolysis via activation of the PI3K/AKT pathway. PLEKHG2 was a potential therapeutic target and biomarker for poor prognosis of NSCLC.

Expression analyses of PLEKHG2, a Rho family-specific guanine nucleotide exchange factor, during mouse brain development

Abnormalities of PLEKHG2 gene, encoding a Rho family-specific guanine nucleotide exchange factor, are involved in microcephaly with intellectual disability. However, not only the role of PLEKHG2 in the developmental process but also its expression profile is unknown. In this study, we prepared a specific antibody against PLEKHG2 and carried out expression analyses with mouse tissues. In western blotting, PLEKHG2 exhibited a tissue-dependent expression profile in adult mouse and was expressed in a developmental stage-dependent manner in brain. Then, in immunohistochemical analyses, while PLEKHG2 was observed in the cortical plate and ventricular zone surface of the cerebral cortex at embryonic day 14, it came to be distributed throughout the cerebral cortex in layer II/III and V during corticogenesis. PLEKHG2 was also detected mainly in the nucleus of neurons in the hippocampal CA regions and dentate gyrus at P7. Notably, the nuclear accumulation disappeared at P30 and PLEKHG2 came to be located at the axons and/or dendrites at this time point. Moreover, in vitro immunofluorescence revealed that PLEKHG2 was at least partially localized at both excitatory and inhibitory synapses in primary cultured hippocampal neurons. These results suggest roles of PLEKHG2 in the development of the central nervous tissue and synaptic function.

STAU1 selectively regulates the expression of inflammatory and immune response genes and alternative splicing of the nerve growth factor receptor signaling pathway

Double‑stranded RNA‑binding protein Staufen homolog 1 (STAU1) is a highly conserved multifunctional double‑stranded RNA‑binding protein, and is a key factor in neuronal differentiation. RNA sequencing was used to analyze the overall transcriptional levels of the upregulated cells by STAU1 and control cells, and select alternative splicing (AS). It was determined that the high expression of STAU1 led to changes in the expression levels of a variety of inflammatory and immune response genes, including IFIT2, IFIT3, OASL, and CCL2. Furthermore, STAU1 was revealed to exert a significant regulatory effect on the AS of genes related to the 'nerve growth factor receptor signaling pathway'. This is of significant importance for neuronal survival, differentiation, growth, post‑damage repair, and regeneration. In conclusion, overexpression of STAU1 was associated with immune response and regulated AS of pathways related to neuronal growth and repair. In the present study, the whole transcriptome of STAU1 expression was first analyzed, which laid a foundation for further understanding the key functions of STAU1.

Novel Prognostic Markers in Triple-Negative Breast Cancer Discovered by MALDI-Mass Spectrometry Imaging

There are no widely-accepted prognostic markers currently available to predict outcomes in patients with triple-negative breast cancer (TNBC), and no targeted therapies with confirmed benefit. We have used MALDI mass spectrometry imaging (MSI) of tryptic peptides to compare regions of cancer and benign tissue in 10 formalin-fixed, paraffin-embedded sections of TNBC tumors. Proteins were identified by reference to a peptide library constructed by LC-MALDI-MS/MS analyses of the same tissues. The prognostic significance of proteins that distinguished between cancer and benign regions was estimated by Kaplan-Meier analysis of their gene expression from public databases. Among peptides that distinguished between cancer and benign tissue in at least 3 tissues with a ROC area under the curve >0.7, 14 represented proteins identified from the reference library, including proteins not previously associated with breast cancer. Initial network analysis using the STRING database showed no obvious functional relationships except among collagen subunits COL1A1, COL1A2, and COL63A, but manual curation, including the addition of EGFR to the analysis, revealed a unique network connecting 10 of the 14 proteins. Kaplan-Meier survival analysis to examine the relationship between tumor expression of genes encoding the 14 proteins, and recurrence-free survival (RFS) in patients with basal-like TNBC showed that, compared to low expression, high expression of nine of the genes was associated with significantly worse RFS, most with hazard ratios >2. In contrast, in estrogen receptor-positive tumors, high expression of these genes showed only low, or no, association with worse RFS. These proteins are proposed as putative markers of RFS in TNBC, and some may also be considered as possible targets for future therapies.

The interaction between PLEKHG2 and ABL1 suppresses cell growth via the NF-κB signaling pathway in HEK293 cells

The Rho family small GTPases mediate cell responses through actin cytoskeletal rearrangement. We previously reported that PLEKHG2, a Rho-specific guanine nucleotide exchange factor, is regulated via interaction with several proteins. We found that PLEKHG2 interacted with non-receptor tyrosine kinase ABL1, but the cellular function remains unclear. Here, we show that the interaction between PLEKHG2 and ABL1 attenuated the PLEKHG2-induced serum response element-dependent gene transcription in a tyrosine phosphorylation-independent manner. PLEKHG2 and ABL1 were co-localized and accumulated within cells co-expressing PLEKHG2 and ABL1. The cellular fractionation analysis suggested that the accumulation involved actin cytoskeletal reorganization. We also revealed that the co-expression of PLEKHG2 with ABL1, but not BCR-ABL, suppressed cell growth and synergistically enhanced NF-κB-dependent gene transcription. The cell growth suppression was canceled by co-expression with IκBα, a member of the NF-κB inhibitor protein family. This study suggests that the interaction between PLEKHG2 and ABL1 suppresses cell growth through intracellular protein accumulation via the NF-κB signaling pathway.

Brain Region and Isoform-Specific Phosphorylation Alters Kalirin SH2 Domain Interaction Sites and Calpain Sensitivity

Kalirin7 (Kal7), a postsynaptic Rho GDP/GTP exchange factor (RhoGEF), plays a crucial role in long-term potentiation and in the effects of cocaine on behavior and spine morphology. The KALRN gene has been linked to schizophrenia and other disorders of synaptic function. Mass spectrometry was used to quantify phosphorylation at 26 sites in Kal7 from individual adult rat nucleus accumbens and prefrontal cortex before and after exposure to acute or chronic cocaine. Region- and isoform-specific phosphorylation was observed along with region-specific effects of cocaine on Kal7 phosphorylation. Evaluation of the functional significance of multisite phosphorylation in a complex protein like Kalirin is difficult. With the identification of five tyrosine phosphorylation (pY) sites, a panel of 71 SH2 domains was screened, identifying subsets that interacted with multiple pY sites in Kal7. In addition to this type of reversible interaction, endoproteolytic cleavage by calpain plays an essential role in long-term potentiation. Calpain cleaved Kal7 at two sites, separating the N-terminal domain, which affects spine length, and the PDZ binding motif from the GEF domain. Mutations preventing phosphorylation did not affect calpain sensitivity or GEF activity; phosphomimetic mutations at specific sites altered protein stability, increased calpain sensitivity, and reduced GEF activity.

Specific activation of PLEKHG2-induced serum response element-dependent gene transcription by four-and-a-half LIM domains (FHL) 1, but not FHL2 or FHL3

PLEKHG2 is a Gβγ- and Gαs-dependent guanine nucleotide exchange factor for Rac1 and Cdc42 small GTPases and has been shown to mediate signaling pathways such as those for actin cytoskeletal reorganization and serum response element (SRE)-dependent gene transcription. We have shown that the four-and-a-half LIM domains (FHL) 1 acts as a positive regulator of PLEKHG2. Here, we evaluated the other FHL family members and found that the FHL1A specifically regulate the PLEKHG2 activity. Moreover, FHL1A further enhanced Gβγ- and PLEKHG2-induced SRE-dependent gene transcription, whereas FHL1A partially restored the attenuated PLEKHG2-induced SRE-dependent gene transcription by Gαs. Our results suggest that FHL1A specifically interacts with PLEKHG2 to regulate a function of PLEKHG2 that is modified by the interaction of Gβγ and Gαs.

Four-and-a-half LIM Domains 1 (FHL1) Protein Interacts with the Rho Guanine Nucleotide Exchange Factor PLEKHG2/FLJ00018 and Regulates Cell Morphogenesis

PLEKHG2/FLJ00018 is a Gβγ-dependent guanine nucleotide exchange factor for the small GTPases Rac and Cdc42 and has been shown to mediate the signaling pathways leading to actin cytoskeleton reorganization. Here we showed that the zinc finger domain-containing protein four-and-a-half LIM domains 1 (FHL1) acts as a novel interaction partner of PLEKHG2 by the yeast two-hybrid system. Among the isoforms of FHL1 (i.e. FHL1A, FHL1B, and FHL1C), FHL1A and FHL1B interacted with PLEKHG2. We found that there was an FHL1-binding region at amino acids 58-150 of PLEKHG2. The overexpression of FHL1A but not FHL1B enhanced the PLEKHG2-induced serum response element-dependent gene transcription. The co-expression of FHL1A and Gβγ synergistically enhanced the PLEKHG2-induced serum response element-dependent gene transcription. Increased transcription activity was decreased by FHL1A knock-out with the CRISPR/Cas9 system. Compared with PLEKHG2-expressing cells, the number and length of finger-like protrusions were increased in PLEKHG2-, Gβγ-, and FHL1A-expressing cells. Our results provide evidence that FHL1A interacts with PLEKHG2 and regulates cell morphological change through the activity of PLEKHG2.

Tyrosine Phosphorylation of SGEF Regulates RhoG Activity and Cell Migration

SGEF and Ephexin4 are members of the Ephexin subfamily of RhoGEFs that specifically activate the small GTPase RhoG. It is reported that Ephexin1 and Ephexin5, two well-characterized Ephexin subfamily RhoGEFs, are tyrosine-phosphorylated by Src, and that their phosphorylation affect their activities and functions. In this study, we show that SGEF, but not Ephexin4, is tyrosine-phosphorylated by Src. Tyrosine phosphorylation of SGEF suppresses its interaction with RhoG, the elevation of RhoG activity, and SGEF-mediated promotion of cell migration. We identified tyrosine 530 (Y530), which is located within the Dbl homology domain, as a major phosphorylation site of SGEF by Src, and Y530F mutation blocked the inhibitory effect of Src on SGEF. Taken together, these results suggest that the activity of SGEF is negatively regulated by tyrosine phosphorylation of the DH domain.