A Screen for Extracellular Signal-Regulated Kinase-Primed Glycogen Synthase Kinase 3 Substrates Identifies the p53 Inhibitor iASPP

LANA regulates miR-155/GATA3 signaling axis by enhancing c-Jun/c-Fos interaction to promote the proliferation and migration of KSHV-infected cells

Kaposi's sarcoma (KS) is the second most common tumor in people infected with human immunodeficiency virus worldwide, but its pathogenesis is still unclear. In this study, we discovered that the expression of GATA-binding protein 3 (GATA3) was lowly expressed in KS tissues and KSHV-infected cells, while microRNA-155 (miR-155) was highly expressed in KS serum and KSHV-infected cells. miR-155 promoted the proliferation, migration and invasion of KSHV infection by targeting GATA3. Further, The KSHV-encoded protein, the Latency associated nuclear antigen (LANA), promotes the proliferation, migration and invasion of KSHV-infected cells by regulating the miR-155/GATA3 axis. Regarding the molecular mechanism, c-Jun and c-Fos interact to form a complex. LANA upregulates the expression of c-Jun and c-Fos and enhances the formation of c-Jun/c-Fos complex. The complex binds to the -95∼-100 bp site of miR-155 promoter and transcriptionally activates miR-155. All in all, LANA enhances the c-Jun/c-Fos interaction, resulting in enhanced transcriptional regulation of miR-155 by the c-Jun/c-Fos complex, thereby downregulating GATA3 and promoting the proliferation, migration and invasion of KSHV-infected cells. The discovery of LANA/c-Jun/c-Fos/miR-155/GATA3 further refines the pathogenesis of KS, potentially opening a new avenue for developing effective drugs against KS.

GSK-3α/β Activity Negatively Regulates MMP-1/9 Expression to Suppress Mycobacterium tuberculosis Infection

Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) infection is the deadliest infectious disease and a global health problem. Macrophages (Mφs) and neutrophils that can phagocytose Mtb represent the first line of immune response to infection. Glycogen synthase kinase-3α/β (GSK-3α/β) represents a regulatory switch in host immune responses. However, the efficacy and molecular mechanisms of how GSK-3α/β interacts with Mtb infection in Mφs remain undefined. Here, we demonstrated that Mtb infection downregulated GSK-3α/β activity and promoted matrix metalloproteinase-1 (MMP-1) and MMP-9 expressions in Mφs derived from acute monocytic human leukemia THP-1 cells (THP-1-Mφs). We confirmed the upregulation of MMP-9 expression in tissues of TB patients compared with patients of chronic inflammation (CI). In THP-1-Mφs and C57BL/6 mice, GSK-3α/β inhibitor SB216763 significantly increased MMP-1/9 production and facilitated Mtb load, while MMP inhibitors blocked MMP-1/9 expression and Mtb infection. Consistently, GSK-3α/β silencing significantly increased MMP-1/9 expression and Mtb infection, while overexpression of GSK-3α/β and constitutive activated GSK-3α/β mutants significantly reduced MMP-1/9 expression and Mtb infection in THP-1-Mφs. MMP-1/9 silencing reduced Mtb infection, while overexpression of MMP-1/9 promoted Mtb infection in THP-1-Mφs. We further found that GSK-3α/β inhibition increased Mtb infection and MMP-1/9 expression was blocked by ERK1/2 inhibitor. Additionally, we showed that protein kinase C-δ (PKC-δ) and mammalian target of rapamycin (mTOR) reduced GSK-3α/β activity and promoted MMP-1/9 production in Mtb-infected THP-1-Mφs. In conclusion, this study suggests that PKC-δ-mTOR axis suppresses GSK-3α/β activation with acceleration of MMP-1/9 expression through phospho-ERK1/2. These results reveal a novel immune escape mechanism of Mtb and a novel crosstalk between these critical signaling pathways in anti-TB immunity.

RTA and LANA Competitively Regulate let-7a/RBPJ Signal to Control KSHV Replication

The recombination signal binding protein for immunoglobulin kappa J region (RBPJ) has a dual effect on Kaposi's sarcoma-associated herpesvirus (KSHV) replication. RBPJ interaction with replication and transcription activator (RTA) is essential for lytic replication, while the interaction with latency-associated nuclear antigen (LANA) facilitates latent infection. Furthermore, our previous study found that LANA decreased RBPJ through upregulating miRNA let-7a. However, it is unclear whether RTA regulates the expression of RBPJ. Here, we show RTA increases RBPJ by decreasing let-7a. During KSHV replication, the RBPJ expression level was positively correlated with the RTA expression level and negatively correlated with the LANA expression level. The let-7a expression level was inverse to RBPJ. Knockdown of RBPJ inhibited the self-activation of RTA promoter and LANA promoter and weakened LANA's inhibition of RTA promoter. Collectively, these findings indicate that RTA and LANA compete for let-7a/RBPJ signal to control the KSHV replication. Regulating the RBPJ expression level by RTA and LANA plays an important role during KSHV replication.

GSK-3β Can Regulate the Sensitivity of MIA-PaCa-2 Pancreatic and MCF-7 Breast Cancer Cells to Chemotherapeutic Drugs, Targeted Therapeutics and Nutraceuticals

Glycogen synthase kinase-3 (GSK-3) is a regulator of signaling pathways. KRas is frequently mutated in pancreatic cancers. The growth of certain pancreatic cancers is KRas-dependent and can be suppressed by GSK-3 inhibitors, documenting a link between KRas and GSK-3. To further elucidate the roles of GSK-3β in drug-resistance, we transfected KRas-dependent MIA-PaCa-2 pancreatic cells with wild-type (WT) and kinase-dead (KD) forms of GSK-3β. Transfection of MIA-PaCa-2 cells with WT-GSK-3β increased their resistance to various chemotherapeutic drugs and certain small molecule inhibitors. Transfection of cells with KD-GSK-3β often increased therapeutic sensitivity. An exception was observed with cells transfected with WT-GSK-3β and sensitivity to the BCL2/BCLXL ABT737 inhibitor. WT-GSK-3β reduced glycolytic capacity of the cells but did not affect the basal glycolysis and mitochondrial respiration. KD-GSK-3β decreased both basal glycolysis and glycolytic capacity and reduced mitochondrial respiration in MIA-PaCa-2 cells. As a comparison, the effects of GSK-3 on MCF-7 breast cancer cells, which have mutant PIK3CA, were examined. KD-GSK-3β increased the resistance of MCF-7 cells to chemotherapeutic drugs and certain signal transduction inhibitors. Thus, altering the levels of GSK-3β can have dramatic effects on sensitivity to drugs and signal transduction inhibitors which may be influenced by the background of the tumor.

An Integrated Systems Biology Approach Identifies the Proteasome as A Critical Host Machinery for ZIKV and DENV Replication

The Zika virus (ZIKV) and dengue virus (DENV) flaviviruses exhibit similar replicative processes but have distinct clinical outcomes. A systematic understanding of virus-host protein-protein interaction networks can reveal cellular pathways critical to viral replication and disease pathogenesis. Here we employed three independent systems biology approaches toward this goal. First, protein array analysis of direct interactions between individual ZIKV/DENV viral proteins and 20,240 human proteins revealed multiple conserved cellular pathways and protein complexes, including proteasome complexes. Second, an RNAi screen of 10,415 druggable genes identified the host proteins required for ZIKV infection and uncovered that proteasome proteins were crucial in this process. Third, high-throughput screening of 6016 bioactive compounds for ZIKV inhibition yielded 134 effective compounds, including six proteasome inhibitors that suppress both ZIKV and DENV replication. Integrative analyses of these orthogonal datasets pinpoint proteasomes as critical host machinery for ZIKV/DENV replication. Our study provides multi-omics datasets for further studies of flavivirus-host interactions, disease pathogenesis, and new drug targets.

A Human Proteome Array Approach to Identifying Key Host Proteins Targeted by Toxoplasma Kinase ROP18

Toxoplasma kinase ROP18 is a key molecule responsible for the virulence of Toxoplasma gondii; however, the mechanisms by which ROP18 exerts parasite virulence via interaction with host proteins remain limited to a small number of identified substrates. To identify a broader array of ROP18 substrates, we successfully purified bioactive mature ROP18 and used it to probe a human proteome array. Sixty eight new putative host targets were identified. Functional annotation analysis suggested that these proteins have a variety of functions, including metabolic process, kinase activity and phosphorylation, cell growth, apoptosis and cell death, and immunity, indicating a pleiotropic role of ROP18 kinase. Among these proteins, four candidates, p53, p38, UBE2N, and Smad1, were further validated. We demonstrated that ROP18 targets p53, p38, UBE2N, and Smad1 for degradation. Importantly, we demonstrated that ROP18 phosphorylates Smad1 Ser-187 to trigger its proteasome-dependent degradation. Further functional characterization of the substrates of ROP18 may enhance understanding of the pathogenesis of Toxoplasma infection and provide new therapeutic targets. Similar strategies could be used to identify novel host targets for other microbial kinases functioning at the pathogen-host interface.

Cell Cycle Regulatory Functions of the KSHV Oncoprotein LANA

Manipulation of cell cycle is a commonly employed strategy of viruses for achieving a favorable cellular environment during infection. Kaposi’s sarcoma-associated herpesvirus (KSHV), the primary etiological agent of several human malignancies including Kaposi’s sarcoma, and primary effusion lymphoma, encodes several oncoproteins that deregulate normal physiology of cell cycle machinery to persist with endothelial cells and B cells and subsequently establish a latent infection. During latency, only a small subset of viral proteins is expressed. Latency-associated nuclear antigen (LANA) is one of the latent antigens shown to be essential for transformation of endothelial cells in vitro. It has been well demonstrated that LANA is critical for the maintenance of latency, episome DNA replication, segregation and gene transcription. In this review, we summarize recent studies and address how LANA functions as an oncoprotein to steer host cell cycle-related events including proliferation and apoptosis by interacting with various cellular and viral factors, and highlight the potential therapeutic strategy of disrupting LANA-dependent signaling as targets in KSHV-associated cancers.

Overexpression of iASPP-SV in glioma is associated with poor prognosis by promoting cell viability and antagonizing apoptosis

Inhibitor of apoptosis-stimulating protein of p53 (iASPP), encoded by PPP1R13L gene, is often overexpressed in human cancers. From the PPP1R13L gene, at least two isoforms, iASPP-L and iASPP-SV, are produced through alternative splicing. However, the role of these isoforms in glioma is still elusive. In this study, we examined the expression of iASPP-SV in astrocytic glioma tissues with different grades and normal human cerebral tissues. The result showed a higher messenger RNA (mRNA) expression level of iASPP-SV in astrocytic glioma patients with World Health Organization (WHO) grade II to IV in comparison to the normal controls. Additionally, mRNA expression level of iASPP-SV was gradually increased with the raise of the grade in glioma. High mRNA expression level of iASPP-SV was significantly associated with malignant WHO grades (P < 0.001). The protein expression level of iASPP-SV was consistent with the mRNA expression level. The Kaplan-Meier analysis revealed that high iASPP-SV mRNA expression significantly affected overall survival and progression-free survival (both P < 0.001). Furthermore, multivariate analysis indicated that the mRNA expression of iASPP-SV was an independent prognostic marker in glioma (P < 0.001). To further explore the role of iASPP-SV in glioma, U87 cells were transfected with iASPP-SV by lentivirus and then treated with temozolomide (TMZ). Overexpression of iASPP-SV promoted the cell viability and downregulated the expression of pro-apoptosis genes (Bax, Puma, p21, and Noxa) to inhibit apoptosis induced by TMZ. Our study provides the first evidence that high iASPP-SV expression may be a novel prognostic factor and therapeutic target for glioma.

Effects of the GSK-3β inhibitor (2Z,3E)-6-bromoindirubin-3'-oxime upon ovarian cancer cells

Ovarian cancer (OC) is a deadly disease, and despite improvements in treatment, overall 5-year survival is low. Glycogen synthase kinase (GSK)-3β is a multifunctional serine/threonine kinase. We wished to ascertain if the GSK-3β inhibitor (2Z,3E)-6-bromoindirubin-3'-oxime, known as "BIO," can suppress OC development. The OC cell lines A2780 and OVCAR3 were exposed to BIO. At different time points, cell proliferation, apoptosis, cell cycle, and cell invasion/cell migration assays were carried out. Phalloidin staining was undertaken to observe lamellipodia formation. Real-time reverse transcription-polymerase chain reaction and western blotting were used to assess expression of messenger RNA (mRNA) and protein of GSK-3β, cyclin D1, matrix metalloproteinase (MMP)-9, and p21. BIO suppressed the proliferation, invasion, and migration of OC cells; reduced lamellipodia formation; and induced G1 arrest of the cell cycle. BIO exposure led to a significant downregulation of mRNA and protein expression of cyclin D1 and MMP9 in comparison with untreated control cells. In contrast, BIO exposure upregulated mRNA and protein expression of p21 in comparison with untreated control cells. Besides, GSK-3β small interfering RNA (siRNA) transfection in ovarian cancer cells also downregulated GSK-3β, cyclin D1, and MMP9 protein expression while upregulated p21 expression. These data suggest that BIO, as an inhibitor of GSK-3β, can suppress OC development. Therefore, BIO could be a candidate drug for the treatment of OC.