Mitotic-Spindle Organizing Protein MztA Mediates Septation Signaling by Suppressing the Regulatory Subunit of Protein Phosphatase 2A-ParA in Aspergillus nidulans

MZT2A serves as a prognostic biomarker and promotes the progression of kidney renal clear cell carcinoma

MZT2A is a novel core component in the γ-tubulin ring complex and aberrantly expressed in some types of tumors. However, MZT2A expression pattern across different cancers and its role in kidney renal clear cell carcinoma have not been sufficiently investigated. A thorough analysis of MZT2A expression landscape across 33 cancer types was conducted, utilizing 712 normal samples and 9807 tumor samples from TCGA (version 37.0), as well as 5112 normal samples from the GTEx databases. MZT2A's impact on KIRC cell viability and proliferation were evaluated through BrdU assays and monitored by cell imaging readers in MZT2A-expressing plasmid or siRNA-transfected cells. Additionally, the effects of MZT2A on cell apoptosis and cell cycle were detected using flow cytometry and Western blot. WGCNA analysis was employed to construct a co-expression gene network associated with MZT2A expression in KIRC, and Pearson correlation coefficient was utilized to examine the relationships between pairs of genes. MZT2A is overexpressed in 25 out of 33 types of cancer, including KIRC. In KIRC, high level of MZT2A was associated with higher clinical stage progression and poorer patients' survival. Downregulation of MZT2A decreased KIRC cell proliferation, retarded cell cycle and promoted apoptosis, while upregulation of MZT2A produced the opposite effects. WGCNA analysis and in vitro experiments revealed that MZT2A activated PI3K/AKT signaling pathway in KIRC. In all, MZT2A was overexpressed in most types of tumors. MZT2A served as an oncogene in KIRC and might be a potential target for guiding future treatments.

Nudt21-mediated alternative polyadenylation of MZT1 3'UTR contributes to pancreatic cancer progression

Alternative polyadenylation (APA) is an important post-transcriptional regulatory mechanism and is involved in many diseases, but its function and mechanism in regulating pancreatic cancer (PC) pathogenesis remain unclear. In this study, we found that the 3' UTR shortening of MZT1 was the most prominent APA event in PC liver metastases. The short-3'UTR isoform exerted a stronger effect in promoting cell proliferation and migration both in vitro and in vivo. NUDT21, a core cleavage factor involved in APA, promoted the usage of proximal polyadenylation sites (PASs) on MZT1 mRNA by binding to the UGUA element located upstream of the proximal PAS. High percentage of distal polyA site usage index of MZT1 was significantly associated with a better prognosis. These findings demonstrate a crucial mechanism that NUDT21-mediated APA of MZT1 could promote the progression of PC. Our findings provided a better understanding of the connection between PC progression and APA machinery.

Downregulation of the ypdA Gene Encoding an Intermediate of His-Asp Phosphorelay Signaling in Aspergillus nidulans Induces the Same Cellular Effects as the Phenylpyrrole Fungicide Fludioxonil

Many eukaryotic histidine-to-aspartate (His-Asp) phosphorelay systems consist of three types of signal transducers: a His-kinase (HK), a response regulator (RR), and a histidine-containing phosphotransfer intermediate (HPt). In general, the HPt acts as an intermediate between the HK and the RR and is indispensable for inducing appropriate responses to environmental stresses. In a previous study, we attempted but were unable to obtain deletion mutants of the ypdA gene in order to characterize its function in the filamentous fungus Aspergillus nidulans. In the present study, we constructed the CypdA strain in which ypdA expression is conditionally regulated by the A. nidulans alcA promoter. We constructed CypdA strains with RR gene disruptions (CypdA-sskAΔ, CypdA-srrAΔ, and CypdA-sskAΔsrrAΔ). Suppression of YpdA induced by ypdA downregulation activated the downstream HogA mitogen-activated protein kinase cascade. YpdA suppression caused severe growth defects and abnormal hyphae, with features such as enhanced septation, a decrease in number of nuclei, nuclear fragmentation, and hypertrophy of vacuoles, both regulated in an SskA-dependent manner. Fludioxonil treatment caused the same cellular responses as ypdA suppression. The growth-inhibitory effects of fludioxonil and the lethality caused by ypdA downregulation may be caused by the same or similar mechanisms and to be dependent on both the SskA and SrrA pathways.

MZT2A promotes NSCLC viability and invasion by increasing Akt phosphorylation via the MOZART2 domain

Mitotic spindle organizing protein 2A (MZT2A) is localized at the centrosome and regulates microtubule nucleation activity in cells. This study assessed the role of MZT2A in non-small-cell lung cancer (NSCLC). Differential MZT2A expression was bioinformatically assessed using TCGA database, the GEPIA database, and Kaplan-Meier survival data to determine the association between MZT2A expression and NSCLC prognosis. Furthermore, NSCLC tissue specimens were evaluated by immunohistochemistry. MZT2A was overexpressed or knocked down in NSCLC cells using cDNA and siRNA, respectively. The cells were subjected to various assays and treated with the selective Akt inhibitor LY294002 or co-transfected with galectin-3-binding protein (LGALS3BP) siRNA. MZT2A mRNA and protein levels were upregulated in NSCLC lesions and MTZ2A expression was associated with poor NSCLC prognosis. MZT2A protein was also highly expressed in NSCLC cells compared with the expression in normal bronchial cells. MZT2A expression promoted NSCLC cell viability and invasion, whereas MTZ2A siRNA had the opposite effect on NSCLC cells in vitro. At the protein level, MZT2A induced Akt phosphorylation, promoting NSCLC proliferation and invasion (but the selective Akt inhibitor blocked these effects) through upregulation of LGALS3BP via the MTZ2A MOZART2 domain, whereas LGALS3BP siRNA suppressed MTZ2A activity in NSCLC cells. The limited in vivo experiments confirmed the in vitro data. In conclusion, MZT2A exhibits oncogenic activity by activating LGALS3BP and Akt in NSCLC. Future studies will assess MTZ2A as a biomarker to predict NSCLC prognosis or as a target in the control of NSCLC progression.

The Scaffold Proteins Paxillin B and α-Actinin Regulate Septation in Aspergillus nidulans via Control of Actin Ring Contraction

Cytokinesis, as the final step of cell division, plays an important role in fungal growth and proliferation. In the filamentous fungus Aspergillus nidulans, defective cytokinesis is able to induce abnormal multinuclear or nonnucleated cells and then result in reduced hyphal growth and abolished sporulation. Previous studies have reported that a conserved contractile actin ring (CAR) protein complex and the septation initiation network (SIN) signaling kinase cascade are required for cytokinesis and septation; however, little is known about the role(s) of scaffold proteins involved in these two important cellular processes. In this study, we show that a septum-localized scaffold protein paxillin B (PaxB) is essential for cytokinesis/septation in A. nidulans The septation defects observed in a paxB deletion strain resemble those caused by the absence of another identified scaffold protein, α-actinin (AcnA). Deletion of α-actinin (AcnA) leads to undetectable PaxB at the septation site, whereas deletion of paxB does not affect the localization of α-actinin at septa. However, deletion of either α-actinin (acnA) or paxB causes the actin ring to disappear at septation sites during cytokinesis. Notably, overexpression of α-actinin acnA partially rescues the septum defects of the paxB mutant but not vice versa, suggesting AcnA may play a dominant role over that of PaxB for cytokinesis and septation. In addition, PaxB and α-actinin affect the septal dynamic localization of MobA, a conserved component of the SIN pathway, suggesting they may affect the SIN protein complex function at septa. Protein pull-down assays combined with liquid chromatography-mass spectrometry identification indicate that α-actinin AcnA and PaxB likely do not directly interact, but presumably belong to an actin cytoskeleton protein network that is required for the assembly and contraction of the CAR. Taken together, findings in this study provide novel insights into the roles of conserved scaffold proteins during fungal septation in A. nidulans.

PP2A Functions during Mitosis and Cytokinesis in Yeasts

Protein phosphorylation is a common mechanism for the regulation of cell cycle progression. The opposing functions of cell cycle kinases and phosphatases are crucial for accurate chromosome segregation and exit from mitosis. Protein phosphatases 2A are heterotrimeric complexes that play essential roles in cell growth, proliferation, and regulation of the cell cycle. Here, we review the function of the protein phosphatase 2A family as the counteracting force for the mitotic kinases. We focus on recent findings in the regulation of mitotic exit and cytokinesis by PP2A phosphatases in S. cerevisiae and other fungal species.

The spindle pole body of Aspergillus nidulans is asymmetrical and contains changing numbers of γ-tubulin complexes

Centrosomes are important microtubule-organizing centers (MTOCs) in animal cells. In addition, non-centrosomal MTOCs (ncMTOCs) are found in many cell types. Their composition and structure are only poorly understood. Here, we analyzed nuclear MTOCs (spindle-pole bodies, SPBs) and septal MTOCs in Aspergillus nidulans They both contain γ-tubulin along with members of the family of γ-tubulin complex proteins (GCPs). Our data suggest that SPBs consist of γ-tubulin small complexes (γ-TuSCs) at the outer plaque, and larger γ-tubulin ring complexes (γ-TuRC) at the inner plaque. We show that the MztA protein, an ortholog of the human MOZART protein (also known as MZT1), interacted with the inner plaque receptor PcpA (the homolog of fission yeast Pcp1) at SPBs, while no interaction nor colocalization was detected between MztA and the outer plaque receptor ApsB (fission yeast Mto1). Septal MTOCs consist of γ-TuRCs including MztA but are anchored through AspB and Spa18 (fission yeast Mto2). MztA is not essential for viability, although abnormal spindles were observed frequently in cells lacking MztA. Quantitative PALM imaging revealed unexpected dynamics of the protein composition of SPBs, with changing numbers of γ-tubulin complexes over time during interphase and constant numbers during mitosis.This article has an associated First Person interview with the first author of the paper.

Ser/Thr protein phosphatases in fungi: structure, regulation and function

Reversible phospho-dephosphorylation of proteins is a major mechanism for the control of cellular functions. By large, Ser and Thr are the most frequently residues phosphorylated in eukar-yotes. Removal of phosphate from these amino acids is catalyzed by a large family of well-conserved enzymes, collectively called Ser/Thr protein phosphatases. The activity of these enzymes has an enormous impact on cellular functioning. In this work we pre-sent the members of this family in S. cerevisiae and other fungal species, and review the most recent findings concerning their regu-lation and the roles they play in the most diverse aspects of cell biology.

Molecular Characteristics of the Conserved Aspergillus nidulans Transcription Factor Mac1 and Its Functions in Response to Copper Starvation

Copper is an essential cofactor of enzymes during a variety of biochemical processes. Therefore, Cu acquisition plays critical roles in cell survival and proliferation, especially during Cu starvation. Knowledge of the key motif(s) by which the low-Cu-responsive transcription factor Mac1 senses Cu is important for understanding how Cu uptake is controlled. Findings in this study demonstrated that the Cu fist motif, but not Cys-rich motifs, is essential for Mac1-mediated Cu uptake in Aspergillus. In addition, Cu transporters CtrA2 and CtrC are both required for Mac1-mediated Cu uptake during Cu starvation in A. nidulans, indicating that species-specific machinery exists for Cu acquisition in Aspergillus.

Copper (Cu) is an essential trace element in all organisms, and Cu acquisition during periods of starvation is important for cell survival and proliferation. Although the Cu starvation-responsive transcription factor Mac1 as well as its targeted Cu transporters have been identified in Aspergillus fumigatus, the molecular mechanisms of Mac1-mediated Cu acquisition have not yet been investigated in Aspergillus. We demonstrated that Mac1 and its regulated Cu transporters are required for growth and conidiophore development during Cu starvation in Aspergillus nidulans. Moreover, A. nidulans Mac1 (AnMac1) showed highly functional conservation with the A. fumigatus homolog but not with homologs in Saccharomyces cerevisiae and Schizosaccharomyces pombe. Molecular characterization of Mac1 in A. nidulans demonstrated that the “Cu fist” motif (i.e., residues 1 through 40) harboring Cys, RGHR, and GRP residues is required for the Mac1-mediated low-Cu response but not the Cys-rich motifs REP-I and REP-II. Notably, overexpression of either the CtrA2 Cu transporter or the CtrC Cu transporter individually was unable to functionally rescue the defects in the AnMac1 deletion strain, implying that Cu uptake might require both CtrA2 and CtrC during Cu starvation, which is different from results seen with A. fumigatus. Findings in this study further suggest that the conserved Mac1-mediated Cu uptake machinery in A. fumigatus and A. nidulans is also species specific.

IMPORTANCE Copper is an essential cofactor of enzymes during a variety of biochemical processes. Therefore, Cu acquisition plays critical roles in cell survival and proliferation, especially during Cu starvation. Knowledge of the key motif(s) by which the low-Cu-responsive transcription factor Mac1 senses Cu is important for understanding how Cu uptake is controlled. Findings in this study demonstrated that the Cu fist motif, but not Cys-rich motifs, is essential for Mac1-mediated Cu uptake in Aspergillus. In addition, Cu transporters CtrA2 and CtrC are both required for Mac1-mediated Cu uptake during Cu starvation in A. nidulans, indicating that species-specific machinery exists for Cu acquisition in Aspergillus.