Cell cycle-dependent phosphorylation of IQGAP is involved in assembly and stability of the contractile ring in fission yeast

A novel cell biological tool to explain mechanics and dynamics in fission yeast

The Rho guanosine triphosphatase hydrolase enzyme (GTPase) is required for the control of the actin cytoskeleton, but its activation in vivo condition is unknown. The study's goal was to find a new synthetic nanobody VHH (P-36 tagged with mNeonGreen) that interacts strongly with the Rho GTPase. We present the first novel synthetic nanobody, VHH (P-36 tagged with mNeonGreen), tested in fission yeast cells and found to have a particular interaction with Rho1GTPase. Plasmids were constructed by using of certain enzymes to digest the pDUAL-pef1a vector plasmid to produce a protein that was encoded by cloned genes. A varied VHH library was created synthetically, then transformed into yeast cells, and positive clones were chosen using chemical agents. To investigate protein interactions and cellular reactions, several studies were carried out, such as live cell imaging, growth curve analysis, coimmunoprecipitation, structural analysis, and cell therapies. Prism and RStudio were used for the statistical analysis. The presence of VHH (P-36) has no effect on the growth pattern making it an appropriate model for studying cytokinesis in vivo. According to a computational biological study, its affinity to interact with Rho1GTPase with all the complementarity-determining region (CDR) regions found on VHH (P-36) is extremely strong. We were able to track its subcellular target by localization using a fluorescent confocal microscope, ensuring the maintenance of cell polarity and morphology. Spheroplast analysis revealed a circular-shaped cell with an even distribution of Rho1 tagged VHH (P-36), indicating that the interaction occurs near the plasma membrane. The introduction of latrunculin-A (Lat-A) disrupted Rho GTPase localization, demonstrating the control over actin production, and the cell did not show evidence of mitotic phase commencement while Lat-A was present. Finally, this important biological tool can aid in our understanding of the mechanics and dynamics of cytokinesis in relation to Rho1GTPase.

Changes in glycated myofibrillar proteins conformation on the formation of Nε-carboxymethyllysine under gradient thermal conditions

N^ε-carboxymethyllysine (CML), a frequently used marker of advanced glycation end products (AGEs) in food, was generated in food processing easily and caused changes in myofibrillar proteins (MPs) characterization. The relevance between glycosylated MPs structure alternation and CML formation under thermal conditions have been reported. However, the correlation mechanism was not clear yet. In this work, the influence of gradient heating (50℃, 60℃, 70℃, 80℃, and 90℃) on the different degrees of glycated MPs, which determined the correlation with CML formation in protein structural changes of MPs. In the rising stage of the CML level, glycation accelerated the fibrillation and aggregation behavior of MPs during heating and increased surface hydrophobicity and particle size. The protein cross-linking affected the protein modification caused by heating and glycation. This work highlights the substantial influences of glycosylation and thermal treatments on MPs, which transformed the MPs structural characteristics and CML level.

Comprehensive analysis of the expression and prognosis for IQ motif-containing GTPase-activating proteins in hepatocellular carcinoma

BACKGROUND

IQ motif-containing GTPase-activating proteins (IQGAPs) are a group of scaffold proteins which have been identified to be involved in tumor initiation and progression in diverse types of cancer. Clinical studies and experimental evidence suggest that IQGAPs play an essential role in hepatocellular carcinoma (HCC) progression and alterations in their expression are closely related to patient prognosis. However, the different expression patterns and prognostic values of all three IQGAP isoforms in HCC have not yet been analyzed simultaneously.

METHODS

We analyzed the transcriptional and survival data of IQGAPs in HCC patients using Oncomine, UALCAN, Kaplan-Meier Plotter, cBioPortal, and GeneMANIA. We further examined tumor and adjacent normal tissues from 250 HCC patients using immunohistochemistry to assess the relationship between IQGAPs expression and clinicopathological features and validate the prognostic value of IQGAPs. In addition, we analyzed transcriptional changes of IQGAPs with regards to survival data in HCC patients from the TCGA-LIHC (liver hepatocellular carcinoma) cohort to validate our results.

RESULTS

We found that the expression levels of IQGAP1 and 3 were significantly elevated in HCC tissues than in normal liver tissues, whereas the expression level of IQGAP2 was decreased in the former than in the latter. The clinical data showed that positive IQGAP1 expression was associated with larger tumor size, advanced tumor-node-metastasis (TNM) stage, poor relapse-free survival (RFS), and overall survival (OS), and positive IQGAP3 expression was associated with poorer tumor differentiation, RFS, and OS. Conversely, positive IQGAP2 expression predicted less tumor numbers and microvascular invasion, as well as higher RFS and OS in these patients.

CONCLUSIONS

IQGAPs may serve as new prognostic biomarkers and potential targets for precision therapy in HCC.

Role of IQ Motif-Containing GTPase-Activating Proteins in Hepatocellular Carcinoma

IQ motif-containing GTPase-activating proteins (IQGAPs) are a class of scaffolding proteins, including IQGAP1, IQGAP2, and IQGAP3, which govern multiple cellular activities by facilitating cytoskeletal remodeling and cellular signal transduction. The role of IQGAPs in cancer initiation and progression has received increasing attention in recent years, especially in hepatocellular carcinoma (HCC), where the aberrant expression of IQGAPs is closely related to patient prognosis. IQGAP1 and 3 are upregulated and are considered oncogenes in HCC, while IQGAP2 is downregulated and functions as a tumor suppressor. This review details the three IQGAP isoforms and their respective structures. The expression and role of each protein in different liver diseases and mainly in HCC, as well as the underlying mechanisms, are also presented. This review also provides a reference for further studies on IQGAPs in HCC.

Laser ablation reveals the impact of Cdc15p on the stiffness of the contractile

The mechanics that govern the constriction of the contractile ring remain poorly understood yet are critical to understanding the forces that drive cytokinesis. We used laser ablation in fission yeast cells to unravel these mechanics focusing on the role of Cdc15p as a putative anchoring protein. Our work shows that the severed constricting contractile ring recoils to a finite point leaving a gap that can heal if less than ∼1 µm. Severed contractile rings in Cdc15p-depleted cells exhibit an exaggerated recoil, which suggests that the recoil is limited by the anchoring of the ring to the plasma membrane. Based on a physical model of the severed contractile ring, we propose that Cdc15p impacts the stiffness of the contractile ring more than the viscous drag.

Cdk1 phosphorylation of fission yeast paxillin inhibits its cytokinetic ring localization

Divisions of the genetic material and cytoplasm are coordinated spatially and temporally to ensure genome integrity. This coordination is mediated in part by the major cell cycle regulator cyclin-dependent kinase (Cdk1). Cdk1 activity peaks during mitosis, but during mitotic exit/cytokinesis Cdk1 activity is reduced, and phosphorylation of its substrates is reversed by various phosphatases including Cdc14, PP1, PP2A, and PP2B. Cdk1 is known to phosphorylate several components of the actin- and myosin-based cytokinetic ring (CR) that mediates division of yeast and animal cells. Here we show that Cdk1 also phosphorylates the Schizosaccharomyces pombe CR component paxillin Pxl1. We determined that both the Cdc14 phosphatase Clp1 and the PP1 phosphatase Dis2 contribute to Pxl1 dephosphorylation at mitotic exit, but PP2B/calcineurin does not. Preventing Pxl1 phosphorylation by Cdk1 results in increased Pxl1 levels, precocious Pxl1 recruitment to the division site, and increased duration of CR constriction. In vitro Cdk1-mediated phosphorylation of Pxl1 inhibits its interaction with the F-BAR domain of the cytokinetic scaffold Cdc15, thereby disrupting a major mechanism of Pxl1 recruitment. Thus, Pxl1 is a novel substrate through which S. pombe Cdk1 and opposing phosphatases coordinate mitosis and cytokinesis.

Phosphorylation in the intrinsically disordered region of F-BAR protein Imp2 regulates its contractile ring recruitment

The F-BAR protein Imp2 is an important contributor to cytokinesis in the fission yeast, Schizosaccharomyces pombe. Because cell cycle regulated phosphorylation of the central intrinsically disordered region (IDR) of the Imp2 paralog, Cdc15, controls Cdc15 oligomerization state, localization, and ability to bind protein partners, we investigated whether Imp2 is similarly phosphoregulated. We found that Imp2 is endogenously phosphorylated on 28 sites within its IDR with the bulk of phosphorylation being constitutive. In vitro, casein kinase 1 (CK1) Hhp1 and Hhp2 can phosphorylate 17 sites and Cdk1 the remaining 11 sites. Mutations that prevent Cdk1 phosphorylation result in precocious Imp2 recruitment to the cell division site, and mutations designed to mimic these phosphorylation events delay Imp2 CR accumulation. Mutations that eliminated CK1 phosphorylation sites allowed CR sliding, and phosphomimetic substitutions at these sites reduced Imp2 protein levels and slowed CR constriction. Thus, like Cdc15, the Imp2 IDR is phosphorylated at many sites by multiple kinases. In contrast to Cdc15, for which phosphorylation plays a major cell cycle regulatory role, Imp2 phosphorylation is primarily constitutive with milder effects on localization and function.