Distribution of PDLIM1 at actin-rich structures generated by invasive and adherent bacterial pathogens

Candidatus Liberibacter asiaticus exploits cytoskeletal system of psyllid vector for circulative propagative infection

The citrus disease Huanglongbing (HLB) in Asia and the US is caused by Candidatus Liberibacter asiaticus (CLas), which is primarily transmitted by Diaphorina citri, also known as Asian citrus psyllid in a persistent and propagative manner. However, the exact mechanisms underlying CLas circulation within D. citri remain largely unclear. Here, immunofluorescence microscopy and electron microscopy were utilized to track the sequential infection of CLas in D. citri, from alimentary canal to salivary glands, and ultimately to the plant host. CLas was found to initially infect the epithelium of filter chamber, after which it rapidly spreads to visceral muscles for further infection throughout the alimentary canal. The rapid spread in D. citri adults causes the duration of CLas circulation to be as short as 9 days. The duration of latent period may be explained by the recruitment of cytoskeletal α-actinin by the outer membrane protein (OMP) of CLas. Inhibition of actin filament or knocking down the expression of α-actinin significantly suppresses CLas cytoskeleton-dependent infection in and spread among D. citri organs. Injection of prokaryotically expressed OMP into D. citri also recruits α-actinin, resembling the natural infection of CLas. Our studies showed that CLas exploits α-actinin and remolds actin machinery of D. citri for overcoming the midgut release barrier, facilitating its circulation in the vector. By shedding light on these mechanisms, this report reveals more detailed mechanisms in CLas infection in D. citri, and offers a plausible explanation for rapid dissemination of HLB in nature from the perspective of psyllid transmission.

Regulation of lymphoma in vitro by CLP36 through the PI3K/AKT/CREB signaling pathway

Background

CLP36 is also known as PDZ and LIM Domain 1 (PDLIM1) that is a ubiquitously-expressed α-actinin-binding cytoskeletal protein involved in carcinogenesis, and our current study aims to explore its involvement in lymphoma.

Methods

Accordingly, the CLP36 expression pattern in lymphoma and its association with the overall survival was predicted. Then, qPCR was applied to gauge CLP36 expression in lymphoma cells and determine the knockdown efficiency. The survival, proliferation and apoptosis of CLP36-silencing lymphoma cells were tested. Cell viability, proliferation and apoptosis were assessed based on cell counting kit-8 (CCK-8) assay, colony formation assay, EdU staining, and flow cytometry, respectively. Additionally, qPCR was used to calculate the expressions of proteins associated with metastasis and apoptosis, while immunoblotting was employed to determine the phosphorylation status of phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/cAMP-response element binding protein (CREB).

Results

CLP36 expression was relatively higher in lymphoma, which was associated with a poor prognosis. Also, CLP36 was highly-expressed in lymphoma cells and the silencing of CLP36 contributed to the suppressed survival and proliferation as well as the enhanced apoptosis of lymphoma cells. Further, CLP36 silencing repressed the expressions of Cadherin 2 (CDH2) and Vimentin (VIM) yet promoted those of Bax and Caspase 3 in lymphoma cells, concurrent with the reduction on the phosphorylation of PI3K, AKT and CREB, all of which were confirmed to be positively correlated with CLP36.

Conclusion

This study, so far as we are concerned, provided evidence on the involvement of CLP36/PI3K/AKT/CREB axis in lymphoma, which may be contributive for the identification on the relevant molecular targets of lymphoma.

Circ ubiquitin-like-containing plant homeodomain and RING finger domains protein 1 increases the stability of G9a and ubiquitin-like-containing plant homeodomain and RING finger domains protein 1 messenger RNA through recruiting eukaryotic translation initiation factor 4A3, transcriptionally inhibiting PDZ and homeobox protein domain protein 1, and promotes the metastasis of hepatocellular carcinoma

BACKGROUND AND AIM

Circular ubiquitin-like, containing PHD and ring finger domains 1 (circUHRF1) is aberrantly upregulated in human hepatocellular carcinoma (HCC) tissues. However, the underlying molecular mechanisms remain obscure. The present study aimed at elucidating the interactive function of circUHRF1-G9a-ubiquitin-like, containing PHD and ring finger domains 1 (UHRF1) mRNA-eukaryotic translation initiation factor 4A3 (EIF4A3)-PDZ and LIM domain 1 (PDLIM1) network in HCC.

METHODS

Expression of circUHRF1, mRNAs of G9a, UHRF1, PDLIM1, epithelial-mesenchymal transition (EMT)-related proteins, and Hippo-Yap pathway components was determined by quantitative polymerase chain reaction (Q-PCR), immunofluorescence, or Western blot analysis. Tumorigenic and metastatic capacities of HCC cells were examined by cellular assays including Cell Counting Kit-8, colony formation, wound healing, and transwell assays. Molecular interactions between EIF4A3 and UHRF1 mRNA were detected by RNA pull-down experiment. Complex formation between UHRF1 and PDLIM1 promoter was detected by chromatin immunoprecipitation assay. Co-immunoprecipitation was performed to examine the binding between UHRF1 and G9a.

RESULTS

Circular ubiquitin-like, containing PHD and ring finger domains 1, G9a, and UHRF1 were upregulated, while PDLIM1 was downregulated in HCC tissue samples and cell lines. Cellular silencing of circUHRF1 repressed HCC proliferation, invasion, migration, and EMT. G9a formed a complex with UHRF1 and inhibited PDLIM1 transcription.

CONCLUSION

Eukaryotic translation initiation factor 4A3 regulated circUHRF1 expression by binding to UHRF1 mRNA promoter. circUHRF1 increased the stability of G9a and UHRF1 mRNAs through recruiting EIF4A3. Overexpression of circUHRF1 aggravated HCC progression through Hippo-Yap pathway and PDLIM1 inhibition. By elucidating the molecular function of circUHRF1-G9a-UHRF1 mRNA-EIF4A3-PDLIM1 network, our data shed light on the HCC pathogenesis and suggest a novel therapeutic strategy for future HCC treatment.

Decreased PDLIM1 expression in endothelial cells contributes to the development of intracranial aneurysm

INTRODUCTION

Intracranial aneurysm (IA) is a common vascular enlargement that occurs in the wall of cerebral vessels and frequently leads to fatal subarachnoid hemorrhage. PDZ and LIM domain protein 1 (PDLIM1) is a cytoskeletal protein that functions as a platform for multiple protein complex formation. However, whether PDLIM is involved in the pathogenesis of IA remains poorly understood.

METHODS

Loss-of-function and gain-of-function strategies were employed to determine the in vitro roles of PDLIM1 in vascular endothelial cells (VECs). A rat model of IA was generated to study the role of PDLIM1 in vivo. Gene expression profiling, Western blotting, and dual luciferase reporter assays were performed to uncover the underlying cellular mechanism. Clinical IA samples were used to determine the expression of PDLIM1 and its downstream signaling molecules.

RESULTS

PDLIM1 expression was reduced in the endothelial cells of IA and was regulated by Yes-associated protein 1 (YAP1). Genetic silencing of PDLIM1 inhibited the viability, migratory ability, and tube formation ability of VECs. Opposite results were obtained by ectopic expression of PDLIM1. Additionally, PDLIM1 overexpression mitigated IA in vivo. Mechanistic investigations revealed that PDLIM1 promoted the transcriptional activity of β-catenin and induced the expression of v-myc myelocytomatosis viral oncogene homolog (MYC) and cyclin D1 (CCND1). In clinical settings, reduced expression of PDLIM1 and β-catenin downstream target genes was observed in human IA samples.

CONCLUSION

Our study indicates that YAP1-dependent expression of PDLIM1 can inhibit IA development by modulating the activity of the Wnt/β-catenin signaling pathway and that PDLIM1 deficiency in VECs may represent a potential marker of aggressive disease.

Localization of host endocytic and actin-associated proteins during Shigella flexneri intracellular motility and intercellular spreading

Shigella flexneri (S. flexneri), the causative agent of bacillary dysentery, uses an effector-mediated strategy to hijack host cells and cause disease. To propagate and spread within human tissues, S. flexneri bacteria commandeer the host actin cytoskeleton to generate slender actin-rich comet tails to move intracellularly, and later, plasma membrane actin-based protrusions to move directly between adjacent host cells. To facilitate intercellular bacterial spreading, large micron-sized endocytic-like membrane invaginations form at the periphery of neighboring host cells that come into contact with S. flexneri-containing membrane protrusions. While S. flexneri comet tails and membrane protrusions consist primarily of host actin cytoskeletal proteins, S. flexneri membrane invaginations remain poorly understood with only clathrin and the clathrin adapter epsin-1 localized to the structures. Tangentially, we recently reported that Listeria monocytogenes, another actin-hijacking pathogen, exploits an assortment of caveolar and actin-bundling proteins at their micron-sized membrane invaginations formed during their cell-to-cell movement. Thus, to further characterize the S. flexneri disease process, we set out to catalog the distribution of a variety of actin-associated and caveolar proteins during S. flexneri actin-based motility and cell-to-cell spreading. Here we show that actin-associated proteins found at L. monocytogenes comet tails and membrane protrusions mimic those present at S. flexneri comet tails with the exception of α-actinins 1 and 4, which were shed from S. flexneri membrane protrusions. We also demonstrate that all known host endocytic components found at L. monocytogenes membrane invaginations are also present at those formed during S. flexneri infections.

mDia1 Assembles a Linear F-Actin Coat at Membrane Invaginations To Drive Listeria monocytogenes Cell-to-Cell Spreading

Direct cell-to-cell spreading of Listeria monocytogenes requires the bacteria to induce actin-based finger-like membrane protrusions in donor host cells that are endocytosed through caveolin-rich membrane invaginations by adjacent receiving cells. An actin shell surrounds these endocytic sites; however, its structure, composition, and functional significance remain elusive. Here, we show that the formin mDia1, but surprisingly not the Arp2/3 complex, is enriched at the membrane invaginations generated by L. monocytogenes during HeLa and Jeg-3 cell infections. Electron microscopy reveals a band of linear actin filaments that run along the longitudinal axis of the invagination membrane. Mechanistically, mDia1 expression is vital for the assembly of this F-actin shell. mDia1 is also required for the recruitment of Filamin A, a caveola-associated F-actin cross-linking protein, and caveolin-1 to the invaginations. Importantly, mixed-cell infection assays show that optimal caveolin-based L. monocytogenes cell-to-cell spreading correlates with the formation of the linear actin filament-containing shell by mDia1. IMPORTANCE Listeria monocytogenes spreads from one cell to another to colonize tissues. This cell-to-cell movement requires the propulsive force of an actin-rich comet tail behind the advancing bacterium, which ultimately distends the host plasma membrane into a slender bacterium-containing membrane protrusion. These membrane protrusions induce a corresponding invagination in the membrane of the adjacent host cell. The host cell that receives the protrusion utilizes caveolin-based endocytosis to internalize the structures, and filamentous actin lines these membrane invaginations. Here, we set out to determine the structure and function of this filamentous actin "shell." We demonstrate that the formin mDia1, but not the Arp2/3 complex, localizes to the invaginations. Morphologically, we show that this actin is organized into linear arrays and not branched dendritic networks. Mechanistically, we show that the actin shell is assembled by mDia1 and that mDia1 is required for efficient cell-to-cell transfer of L. monocytogenes.

PDLIM1: Structure, function and implication in cancer

PDLIM1, a member of the PDZ-LIM family, is a cytoskeletal protein and functions as a platform to form distinct protein complexes, thus participating in multiple physiological processes such as cytoskeleton regulation and synapse formation. Emerging evidence demonstrates that PDLIM1 is dysregualted in a variety of tumors and plays essential roles in tumor initiation and progression. In this review, we summarize the structure and function of PDLIM1, as well as its important roles in human cancers.