Phospholipase Cγ1 connects the cell membrane pathway to the nuclear receptor pathway in insect steroid hormone signaling

Human T-cell lymphotropic virus type 1 (HTLV-1) grip on T-cells: investigating the viral tapestry of activation

INTRODUCTION

Human T-cell Lymphotropic virus type 1 (HTLV-1) belongs to retroviridae which is connected to two major diseases, including HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and Adult T-cell leukemia/lymphoma (ATLL). This study aims to investigate the mRNA expressions of key proteins correlated to T-cell activation in asymptomatic carriers (ACs) HTLV-1 infected patients, shedding light on early molecular events and T-cell activation following HTLV-1 infection.

MATERIAL AND METHODS

The study involved 40 participants, including 20 ACs and 20 healthy subjects. Blood samples were collected, ELISA assessment for screening and confirmation with PCR for Trans-activating transcriptional regulatory protein (Tax) and HTLV-1 basic leucine zipper factor (HBZ) of the HTLV-1 were done. mRNA expressions of C-terminal Src kinase (CSK), Glycogen Synthase Kinase-3 Beta (GSK3β), Mitogen-Activated Protein Kinase 14 (MAP3K14 or NIK), Phospholipase C Gamma-1 (PLCG1), Protein Tyrosine Phosphatase non-Receptor Type 6 (PTPN6) and Mitogen-Activated Protein Kinase Kinase Kinase-7 (SLP-76) and Mitogen-Activated Protein Kinase14 (MAP3K7 or TAK1) were assayed using RT-qPCR. Statistical analyses were performed using PRISM and SPSS software.

RESULTS

While there were no significant upregulation in CSK and PTPN6 in ACs compared to healthy individuals, expression levels of GSK3β, MAP3K14, PLCG1, SLP-76, and TAK1 were significantly higher in ACs compared to healthy subjects which directly contributes to T-cell activation in the HTLV-1 ACs.

CONCLUSION

HTLV-1 infection induces differential mRNA expressions in key proteins associated with T-cell activation. mRNAs related to T-cell activation showed significant upregulation compared to PTPN6 and CSK which contributed to T-cell regulation. Understanding these early molecular events in ACs may provide potential markers for disease progression and identify therapeutic targets for controlling viral replication and mitigating associated diseases. The study contributes novel insights to the limited literature on T-cell activation and HTLV-1 pathogenesis.

A CTL - Lys immune function maintains insect metamorphosis by preventing gut bacterial dysbiosis and limiting opportunistic infections

BACKGROUND

Gut bacteria are beneficial to the host, many of which must be passed on to host offspring. During metamorphosis, the midgut of holometabolous insects undergoes histolysis and remodeling, and thus risks losing gut bacteria. Strategies employed by holometabolous insects to minimize this risk are obscure. How gut bacteria affect host insects after entering the hemocoel and causing opportunistic infections remains largely elusive.

RESULTS

We used holometabolous Helicoverpa armigera as a model and found low Lactobacillus load, high level of a C-type lectin (CTL) gene CD209 antigen-like protein 2 (CD209) and its downstream lysozyme 1 (Lys1) in the midgut of the wandering stage. CD209 or Lys1 depletion increased the load of midgut Lactobacillus, which further translocate to the hemocoel. In particular, CD209 or Lys1 depletion, injection of Lactobacillus plantarum, or translocation of midgut L. plantarum into the hemocoel suppressed 20-hydroxyecdysone (20E) signaling and delayed pupariation. Injection of L. plantarum decreased triacylglycerol and cholesterol storage, which may result in insufficient energy and 20E available for pupariation. Further, Lysine-type peptidoglycan, the major component of gram-positive bacterial cell wall, contributed to delayed pupariation and decreased levels of triacylglycerols, cholesterols, and 20E, in both H. armigera and Drosophila melanogaster.

CONCLUSIONS

A mechanism by which (Lactobacillus-induced) opportunistic infections delay insect metamorphosis was found, namely by disturbing the homeostasis of lipid metabolism and reducing 20E production. Moreover, the immune function of CTL - Lys was characterized for insect metamorphosis by maintaining gut homeostasis and limiting the opportunistic infections.

MiR-3017b contributes to metamorphosis by targeting sarco/endoplasmic reticulum Ca2+ ATPase in Tribolium castaneum

In recent years, increasing numbers of microRNAs (miRNAs) have been reported to regulate insect metamorphosis. One thousand, one hundred fifty-four miRNAs have been previously identified from Tribolium castaneum by high-throughput sequencing; however, little is known about which miRNAs can participate in metamorphosis, leaving the role of miRNAs in regulating the underlying mechanism elusive. Here, we report the participation of miR-3017b in the metamorphosis of T. castaneum. Temporal profiles revealed that miR-3017b was highly expressed at the late larval stage, but significantly decreased at the early pupal stage. Overexpression of miR-3017b caused larval to pupal to adult metamorphosis arrested. Dual-luciferase reporter assay and miRNA-mRNA interaction assay illustrated that miR-3017b interacts with the coding sequence of sarco/endoplasmic reticulum Ca²⁺ ATPase (SERCA) and suppresses its expression. Knockdown of SERCA caused metamorphosis arrested, similar to that observed in miR-3017b overexpression beetles. Further functional mechanism analyses revealed that 20-hydroxyecdysone application downregulates miR-3017b and up-regulates SERCA expression. The expression level of downstream genes in the 20E pathway was disrupted after overexpressing miR-3017 and the knockdown of SERCA. These results provided evidence miR-3017b-SERCA contributes to metamorphosis by regulating the 20E pathway in T. castaneum. It could advance our understanding of the coordination of 20E and miRNA regulation in insect metamorphosis.

Insulin-like Growth Factor 2 Promotes Tissue-Specific Cell Growth, Proliferation and Survival during Development of Helicoverpa armigera

During development, cells constantly undergo fate choices by differentiating, proliferating, and dying as part of tissue remodeling. However, we only begin to understand the mechanisms of these different fate choices. Here, we took the lepidopteran insect Helicoverpa armigera, the cotton bollworm, as a model to reveal that insulin-like growth factor 2 (IGF-2-like) prevented cell death by promoting cell growth and proliferation. Tissue remodeling occurs during insect metamorphosis from larva to adult under regulation by 20-hydroxyecdysone (20E), a steroid hormone. An unknown insulin-like peptide in the genome of H. armigera was identified as IGF-2-like by sequence analysis using human IGFs. The expression of Igf-2-like was upregulated by 20E. IGF-2-like was localized in the imaginal midgut during tissue remodeling, but not in larval midgut that located nearby. IGF-2-like spread through the fat body during fat body remodeling. Cell proliferation was detected in the imaginal midgut and some fat body cells expressing IGF-2-like. Apoptosis was detected in the larval midgut and some fat body cells that did not express IGF-2-like, suggesting the IGF-2-like was required for cell survival, and IGF-2-like and apoptosis were exclusive, pointing to a survival requirement. Knockdown of Igf-2-like resulted in repression of growth and proliferation of the imaginal midgut and fat body. Our results suggested that IGF-2-like promotes cell growth and proliferation in imaginal tissues, promoting cell death avoidance and survival of imaginal cells during tissue remodeling. It will be interesting to determine whether the mechanism of action of steroid hormones on insulin growth factors is conserved in other species.

iTRAQ Proteomic Analysis of Interactions Between 20E and Phospholipase C in Apolygus lucorum (Meyer-Dür)

Polyphagous Apolygus lucorum has become the dominant insect in Bacillus thuringiensis (Bt) cotton fields. Hormone 20-hydroxyecdysone (20E) regulates multiple insect development and physiology events. 20E responses are controlled by pathways triggered by phospholipase C (PLC)-associated proteins. However, 20E-modulated genes and related proteins that can be affected by PLC still remain unknown. Here, isobaric tag for relative and absolute quantitation (iTRAQ) and immunoblotting techniques were used to compare differentially expressed proteins (DEPs) in A. lucorum in response to the treatment of 20E and the PLC inhibitor U73122 as well as their combination. A total of 1,624 non-redundant proteins and 97, 248, 266 DEPs were identified in the 20E/control, U73122/control, and 20E + U73122/control groups, respectively. Only 8 DEPs, including pathogenesis-related protein 5-like, cuticle protein 19.8, trans-sialidase, larval cuticle protein A2B-like, cathepsin L1, hemolymph juvenile hormone-binding protein, ATP-dependent RNA helicase p62-like, and myosin-9 isoform X1, were detected in all three groups. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the DEPs were involved in diverse signaling pathways. The results were validated by immunoblotting, which highlighted the reliability of proteomics analysis. These findings provided novel insights into the function of PLC in 20E signaling pathway in A. lucorum.

Steroid hormone 20-hydroxyecdysone promotes CTL1-mediated cellular immunity in Helicoverpa armigera

Mermithid nematodes, such as Ovomermis sinensis, are used as biological control agents against many insect pests, including cotton bollworm (Helicoverpa armigera). However, given the host's robust immune system, the infection rate of O. sinensis is low, thus restricting its widespread use. To understand the host defense mechanisms against mermithid nematodes, we identified and characterized a protein involved in the recognition of O. sinensis, the potential O. sinensis-binding protein C-type lectin 1 (HaCTL1a and/or HaCTL1b), which was eluted from the surface of O. sinensis after incubation with H. armigera plasma. HaCTL1b is homologous to the previously reported HaCTL1a protein. HaCTL1 was predominantly expressed in hemocytes and was induced by the steroid hormone 20-hydroxyecdysone through ecdysone receptor (HaEcR) or ultraspiracle (HaUSP), or both. Binding assays confirmed the interactions of the HaCTL1 proteins with O. sinensis but not with Romanomermis wuchangensis, a parasitic nematode of mosquito. Moreover, the HaCTL1 proteins were secreted into the hemocoel and promoted hemocyte-mediated encapsulation and phagocytosis. A knockdown of HaEcR and/or HaUSP resulted in compromised encapsulation and phagocytosis. Thus, HaCTL1 appears to modulate cellular immunity in the defense against parasitic nematodes, and the 20-hydroxyecdysone-HaEcR-HaUSP complex is involved in regulating the process.

Autophagy triggers CTSD (cathepsin D) maturation and localization inside cells to promote apoptosis

CTSD/CathD/CATD (cathepsin D) is a lysosomal aspartic protease. A distinguishing characteristic of CTSD is its dual functions of promoting cell proliferation via secreting a pro-enzyme outside the cells as a ligand, and promoting apoptosis via the mature form of this enzyme inside cells; however, the regulation of its secretion, expression, and maturation is undetermined. Using the lepidopteran insect Helicoverpa armigera, a serious agricultural pest, as a model, we revealed the dual functions and regulatory mechanisms of CTSD secretion, expression, and maturation. Glycosylation of asparagine 233 (N233) determined pro-CTSD secretion. The steroid hormone 20-hydroxyecdysone (20E) promoted CTSD expression. Macroautophagy/autophagy triggered CTSD maturation and localization inside midgut cells to activate CASP3 (caspase 3) and promote apoptosis. Pro-CTSD was expressed in the pupal epidermis and was secreted into the hemolymph to promote adult fat body endoreplication/endoreduplication, cell proliferation, and association. Our study revealed that the differential expression and autophagy-mediated maturation of CTSD in tissues determine its roles in apoptosis and cell proliferation, thereby determining the cell fates of tissues during lepidopteran metamorphosis.Abbreviations: 20E: 20-hydroxyecdysone; 3-MA: 3-methyladenine; ACTB/β-actin: actin beta; AKT: protein kinase B; ATG1: autophagy-related 1; ATG4: autophagy-related 4; ATG5: autophagy-related 5; ATG7: autophagy-related 7; ATG14: autophagy-related 14; BSA: bovine serum albumin; CASP3: caspase 3; CQ: choroquine; CTSD: cathepsin D; DAPI: 4',6-diamidino-2-phenylindole; DMSO: dimethyl sulfoxide; DPBS: dulbecco's phosphate-buffered saline; DsRNA: double-stranded RNA; EcR: ecdysone receptor; EcRE: ecdysone response element; EdU: 5-ethynyl-2´-deoxyuridine; G-m-CTSD: glycosylated-mautre-CTSD; G-pro-CTSD: glycosylated-pro-CTSD; HaEpi: Helicoverpa armigera epidermal cell line; HE staining: hematoxylin and eosin staining; IgG: immunoglobin G; IM: imaginal midgut; JH: juvenile hormone; Kr-h1: krueppel homologous protein 1; LM: larval midgut; M6P: mannose-6-phosphate; PBS: phosphate-buffered saline; PCD: programmed cell death; PNGase: peptide-N-glycosidase F; RFP: red fluorescent protein; RNAi: RNA interference; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; SYX17: syntaxin 17; USP1: ultraspiracle isoform 1.

Phospholipase C gamma (PLCγ) regulates soluble trehalase in the 20E-induced fecundity of Apolygus lucorum

Apolygus lucorum is the dominant pathogenic insect attacking Bacillus thuringiensis (Bt) cotton in China. Additionally, 20-hydroxyecdysone (20E) has important functions in many biological processes, including insect reproduction. Phospholipase C (PLC), which is an essential enzyme for phosphoinositide metabolism, is involved in 20E signal transduction, but its function in 20E-mediated reproduction in A. lucorum remains unclear. In this study, 20E increased AlPLCγ transcription as well as the abundance and activity of the encoded protein during molting and metamorphosis. The 20E treatment also induced the considerable accumulation of two second messengers, inositol triphosphate and diacylglycerol. The expression levels of genes encoding vitellogenin (AlVg) and soluble trehalase (AlTre-1) were similar to those of AlPLCγ, and were upregulated in response to 20E. The silencing of AlPLCγ resulted in downregulated expression of AlTre-1 and AlVg. However, the silencing of AlTre-1 and AlVg did not affect AlPLCγ expression. Moreover, the silencing of AlVg did not alter AlTre-1 expression. Furthermore, an examination of the insect specimens indicated that AlPLCγ is required for female adult reproduction, and that downregulated expression of this gene is associated with decreases in fecundity, adult longevity, and egg hatching rate as well as delayed oocyte maturation. We propose that 20E regulates AlTre-1 expression via AlPLCγ and affects Vg expression as well as ovary development to facilitate the reproductive activities of A. lucorum females.

The homotetramerization of a GPCR transmits the 20-hydroxyecdysone signal and increases its entry into cells for insect metamorphosis

Animal steroid hormones initiate signaling by passive diffusion into cells and binding to their nuclear receptors to regulate gene expression. Animal steroid hormones can initiate signaling via G protein-coupled receptors (GPCRs); however, the underlying mechanisms are unclear. Here, we show that a newly discovered ecdysone-responsive GPCR, ErGPCR-3, transmits the steroid hormone 20-hydroxyecdysone (20E) signal by binding 20E and promoting its entry into cells in the lepidopteran insect Helicoverpa armigera Knockdown of ErGPCR-3 in larvae caused delayed and abnormal pupation, inhibited remodeling of the larval midgut and fat body, and repressed 20E-induced gene expression. Also, 20E induced both the interaction of ErGPCR-3 with G proteins and rapid intracellular increase in calcium, cAMP and protein phosphorylation. ErGPCR-3 was endocytosed by GPCR kinase 2-mediated phosphorylation, and interacted with β-arrestin-1 and clathrin, to terminate 20E signaling under 20E induction. We found that 20E bound to ErGPCR-3 and induced the ErGPCR-3 homodimer to form a homotetramer, which increased 20E entry into cells. Our study revealed that homotetrameric ErGPCR-3 functions as a cell membrane receptor and increases 20E diffusion into cells to transmit the 20E signal and promote metamorphosis.

Silencing of a LIM gene in cotton exhibits enhanced resistance against Apolygus lucorum

Plant bugs (Miridae species) have become major agricultural pests that cause increasing and severe economic damage. Plant-mediated RNA interference (RNAi) is emerging as an eco-friendly, efficient, and reliable strategy for pest management. In this study, we isolated and characterized a lethal gene of Apolygus lucorum and named it Apolygus lucorum LIM (AlLIM), which produced A. lucorum mortality rates ranging from 38% to 81%. Downregulation of the AlLIM gene expression in A. lucorum by injection of a double-stranded RNA (dsRNA) led to muscle structural disorganization that resulted in metamorphosis deficiency and increased mortality. Then we constructed a plant expression vector that enabled transgenic cotton to highly and stably express dsRNA of AlLIM (dsAlLIM) by Agrobacterium-mediated genetic transformation. In the field bioassay, dsAlLIM transgenic cotton was protected from A. lucorum damage with high efficiency, with almost no detectable yield loss. Therefore, our study successfully provides a promising genetically modified strategy to overpower A. lucorum attack.

Label-free quantitative proteomic analysis of insect larval and metamorphic molts

Background

Molting is an essential biological process occurring characteristic times throughout the life cycle of holometabolous insects. However, it is not clear how insects determine the direction of molting to remain status quo or to initiate metamorphosis. To explore the functional factors that determine the direction of molts, liquid chromatography-mass spectrometry was used to identify the molecules involved in larval and metamorphic molting, and the differentially expressed proteins (DEPs) were compared in the two processes.

Results

There were 321 and 1140 DEPs identified in larval and metamorphic molting process, respectively. Bioinformatics analyses show that the amino sugar pathway was up-regulated in both processes. The up-regulated protease contributed to the metamorphosis. In addition, several proteins with different expression patterns in larval-larval and larval-pupal transitions, including Endochitinase, GRIM-19 (Genes associated with retinoid-IFN-induced mortality-19), IDE (Insulin-degrading enzyme), Sorcin (Soluble resistance related calcium binding protein), OBP (Odorant-binding protein-2 precursor), TRAP1(Tumor necrosis factor receptor associated protein-1), etc., were further identified by parallel reaction monitoring, which may play diverse functions in larval-larval and larval-pupal transitions.

Conclusions

These results provide a proteomic insight into molecules involved in larval and metamorphic molts, and will likely improve the current understanding of determination of direction of molts.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12861-020-00227-z.

G protein-coupled receptors function as cell membrane receptors for the steroid hormone 20-hydroxyecdysone

Abstract

G protein-coupled receptors (GPCRs) are cell membrane receptors for various ligands. Recent studies have suggested that GPCRs transmit animal steroid hormone signals. Certain GPCRs have been shown to bind steroid hormones, for example, G protein-coupled estrogen receptor 1 (GPER1) binds estrogen in humans, and Drosophila dopamine/ecdysteroid receptor (DopEcR) binds the molting hormone 20-hydroxyecdysone (20E) in insects. This review summarizes the research progress on GPCRs as animal steroid hormone cell membrane receptors, including the nuclear and cell membrane receptors of steroid hormones in mammals and insects, the 20E signaling cascade via GPCRs, termination of 20E signaling, and the relationship between genomic action and the nongenomic action of 20E. Studies indicate that 20E induces a signal via GPCRs to regulate rapid cellular responses, including rapid Ca²⁺ release from the endoplasmic reticulum and influx from the extracellular medium, as well as rapid protein phosphorylation and subcellular translocation. 20E via the GPCR/Ca²⁺/PKC/signaling axis and the GPCR/cAMP/PKA-signaling axis regulates gene transcription by adjusting transcription complex formation and DNA binding activity. GPCRs can bind 20E in the cell membrane and after being isolated, suggesting GPCRs as cell membrane receptors of 20E. This review deepens our understanding of GPCRs as steroid hormone cell membrane receptors and the GPCR-mediated signaling pathway of 20E (20E-GPCR pathway), which will promote further study of steroid hormone signaling via GPCRs, and presents GPCRs as targets to explore new pharmaceutical materials to treat steroid hormone-related diseases or control pest insects.

Src couples estrogen receptor to the anticipatory unfolded protein response and regulates cancer cell fate under stress

Accumulation of unfolded protein, or other stresses, activates the classical reactive unfolded protein response (UPR). In the recently characterized anticipatory UPR, receptor-bound estrogen, progesterone and other mitogenic hormones rapidly elicit phosphorylation of phospholipase C γ (PLCγ), activating the anticipatory UPR. How estrogen and progesterone activating their receptors couples to PLCγ phosphorylation and anticipatory UPR activation was unknown. We show that the oncogene c-Src is a rate-limiting regulator whose tyrosine kinase activity links estrogen and progesterone activating their receptors to anticipatory UPR activation. Supporting Src coupling estrogen and progesterone to anticipatory UPR activation, we identified extranuclear complexes of estrogen receptor α (ERα):Src:PLCγ and progesterone receptor:Src:PLCγ. Moreover, Src inhibition protected cancer cells against cell death. To probe Src's role, we used the preclinical ERα biomodulator, BHPI, which kills cancer cells by inducing lethal anticipatory UPR hyperactivation. Notably, Src inhibition blocked BHPI-mediated anticipatory UPR activation and the resulting rapid increase in intracellular calcium. After unbiased long-term selection for BHPI-resistant human breast cancer cells, 4/11 BHPI-resistant T47D clones, and nearly all MCF-7 clones, exhibited reduced levels of normally growth-stimulating Src. Notably, Src overexpression by virus transduction restored sensitivity to BHPI. Furthermore, in wild type cells, several-fold knockdown of Src, but not of ERα, strongly blocked BHPI-mediated UPR activation and subsequent HMGB1 release and necrotic cell death. Thus, Src plays a previously undescribed pivotal role in activation of the tumor-protective anticipatory UPR, thereby increasing the resilience of breast cancer cells. This is a new role for Src and the anticipatory UPR in breast cancer.

Phosphoinositide-Dependent Signaling in Cancer: A Focus on Phospholipase C Isozymes

Phosphoinositides (PI) form just a minor portion of the total phospholipid content in cells but are significantly involved in cancer development and progression. In several cancer types, phosphatidylinositol 3,4,5-trisphosphate [PtdIns(3,4,5)P₃] and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P₂] play significant roles in regulating survival, proliferation, invasion, and growth of cancer cells. Phosphoinositide-specific phospholipase C (PLC) catalyze the generation of the essential second messengers diacylglycerol (DAG) and inositol 1,4,5 trisphosphate (InsP₃) by hydrolyzing PtdIns(4,5)P₂. DAG and InsP₃ regulate Protein Kinase C (PKC) activation and the release of calcium ions (Ca²⁺) into the cytosol, respectively. This event leads to the control of several important biological processes implicated in cancer. PLCs have been extensively studied in cancer but their regulatory roles in the oncogenic process are not fully understood. This review aims to provide up-to-date knowledge on the involvement of PLCs in cancer. We focus specifically on PLCβ, PLCγ, PLCδ, and PLCε isoforms due to the numerous evidence of their involvement in various cancer types.

The steroid hormone 20-hydroxyecdysone induces phosphorylation and aggregation of stromal interacting molecule 1 for store-operated calcium entry

Oligomerization of stromal interacting molecule 1 (STIM1) promotes store-operated calcium entry (SOCE); however, the mechanism of STIM1 aggregation is unclear. Here, using the lepidopteran insect and agricultural pest cotton bollworm (Helicoverpa armigera) as a model and immunoblotting, RT-qPCR, RNA interference (RNAi), and ChIP assays, we found that the steroid hormone 20-hydroxyecdysone (20E) up-regulates STIM1 expression via G protein-coupled receptors (GPCRs) and the 20E nuclear receptor (EcRB1). We also identified an ecdysone-response element (EcRE) in the 5'-upstream region of the STIM1 gene and also noted that STIM1 is located in the larval midgut during metamorphosis. STIM1 knockdown in larvae delayed pupation time, prevented midgut remodeling, and decreased 20E-induced gene transcription. STIM1 knockdown in a H. armigera epidermal cell line, HaEpi, repressed 20E-induced calcium ion influx and apoptosis. Moreover, 20E-induced STIM1 clustering to puncta and translocation toward the cell membrane. Inhibitors of GPCRs, phospholipase C (PLC), and inositol trisphosphate receptor (IP3R) repressed 20E-induced STIM1 phosphorylation, and we found that two GPCRs are involved in 20E-induced STIM1 phosphorylation. 20E-induced STIM1 phosphorylation on Ser-485 through protein kinase C (PKC), and we observed that Ser-485 phosphorylation is critical for STIM1 clustering, interaction with calcium release-activated calcium channel modulator 1 (Orai1), calcium ion influx, and 20E-induced apoptosis. These results suggest that 20E up-regulates STIM1 phosphorylation for aggregation via GPCRs, followed by interaction with Orai1 to induce SOCE, thereby promoting apoptosis in the midgut during insect metamorphosis.

The steroid hormone 20-hydroxyecdysone binds to dopamine receptor to repress lepidopteran insect feeding and promote pupation

Holometabolous insects stop feeding at the final larval instar stage and then undergo metamorphosis; however, the mechanism is unclear. In the present study, using the serious lepidopteran agricultural pest Helicoverpa armigera as a model, we revealed that 20-hydroxyecdysone (20E) binds to the dopamine receptor (DopEcR), a G protein-coupled receptor, to stop larval feeding and promote pupation. DopEcR was expressed in various tissues and its level increased during metamorphic molting under 20E regulation. The 20E titer was low during larval feeding stages and high during wandering stages. By contrast, the dopamine (DA) titer was high during larval feeding stages and low during the wandering stages. Injection of 20E or blocking dopamine receptors using the inhibitor flupentixol decreased larval food consumption and body weight. Knockdown of DopEcR repressed larval feeding, growth, and pupation. 20E, via DopEcR, promoted apoptosis; and DA, via DopEcR, induced cell proliferation. 20E opposed DA function by repressing DA-induced cell proliferation and AKT phosphorylation. 20E, via DopEcR, induced gene expression and a rapid increase in intracellular calcium ions and cAMP. 20E induced the interaction of DopEcR with G proteins αs and αq. 20E, via DopEcR, induced protein phosphorylation and binding of the EcRB1-USP1 transcription complex to the ecdysone response element. DopEcR could bind 20E inside the cell membrane or after being isolated from the cell membrane. Mutation of DopEcR decreased 20E binding levels and related cellular responses. 20E competed with DA to bind to DopEcR. The results of the present study suggested that 20E, via binding to DopEcR, arrests larval feeding and promotes pupation.

The steroid hormone 20-hydroxyecdysone (20E) represses insect larval feeding and promotes metamorphosis; however, the mechanism is unclear. The dopamine receptor plays important roles in animal motor function and reward-motivated behavior. Using the serious lepidopteran agricultural pest Helicoverpa armigera as a model, we revealed that 20E binds to DopEcR to block the dopamine pathway and initiates the 20E pathway. Dopamine (DA) binds to the dopamine receptor (DopEcR), a G protein-coupled receptor (GPCR), to regulate cell proliferation, larval feeding, and growth. However, 20E competes with DA to bind to DopEcR, which represses larval feeding and triggers the 20E-pathway, leading to metamorphosis. The results suggested that 20E, via binding to DopEcR, stops larval feeding and promotes pupation, which presented an example of the steroid hormone regulating dopamine receptor and behavior. Our study showed that GPCRs can bind 20E and function as 20E cell membrane receptors.

Vrille is required for larval moulting and metamorphosis of Helicoverpa armigera (Lepidoptera: Noctuidae)

Vrille (Vri), a basic leucine zipper transcription factor, plays important roles in insect circadian clock regulation, tracheal development, proliferation, flight and metamorphosis. Here, Helicoverpa armigera was used as a model to investigate the role of Vri in larval moulting and metamorphosis. Sequence analysis results revealed that H. armigera Vri (HaVri) shares a high amino acid identity with other Lepidoptera Vri homologues. Spatial-temporal expression pattern data showed that HaVri expression was highly abundant in larval moulting and metamorphosis stages and was mainly expressed in the midgut and Malpighian tubule during metamorphosis. HaVri knockdown by RNA interference in the fourth-instar larvae prevented larval moulting, and HaVri knockdown in the fifth-instar larvae suppressed midgut remodelling and delayed or blocked metamorphosis. Further studies confirmed that 20-hydroxyecdysone (20E) activated HaVri expression via its heterodimer receptors, ecdysone receptor (EcRB1) and ultraspiracle protein (USP1), whereas methoprene [juvenile hormone analogue (JHA)] promoted HaVri expression via its intracellular receptor methoprene-tolerant (Met1). However, 20E and JHA can counteract each other in the activation of HaVri expression. Together, the present results suggested that HaVri was involved in larval moulting and metamorphosis and was regulated by 20E and JHA in H. armigera.

Insulin and 20-hydroxyecdysone oppose each other in the regulation of phosphoinositide-dependent kinase-1 expression during insect pupation

Insulin promotes larval growth of insects by stimulating the synthesis of the steroid hormone 20-hydroxyecdysone (20E), which induces pupation and apoptosis. However, the mechanism underlying the coordinate regulation of insect pupation and apoptosis by these two functionally opposing hormones is still unclear. Here, using the lepidopteran insect and serious agricultural pest Helicoverpa armigera (cotton bollworm) as a model, we report that phosphoinositide-dependent kinase-1 (PDK1) and forkhead box O (FoxO) play key roles in these processes. We found that the transcript levels of the PDK1 gene are increased during the larval feeding stages. Moreover, PDK1 expression was increased by insulin, but repressed by 20E. dsRNA-mediated PDK1 knockdown in the H. armigera larvae delayed pupation and resulted in small pupae and also decreased Akt/protein kinase B expression and increased FoxO expression. Furthermore, the PDK1 knockdown blocked midgut remodeling and decreased 20E levels in the larvae. Of note, injecting larvae with 20E overcame the effect of the PDK1 knockdown and restored midgut remodeling. FoxO overexpression in an H. armigera epidermal cell line (HaEpi) did not induce apoptosis, but promoted autophagy and repressed cell proliferation. These results reveal cross-talk between insulin and 20E and that both hormones oppose each other's activities in the regulation of insect pupation and apoptosis by controlling PDK1 expression and, in turn, FoxO expression. We conclude that sufficiently high 20E levels are a key factor for inducing apoptosis during insect pupation.

Intrinsically disordered N-terminal domain of the Helicoverpa armigera Ultraspiracle stabilizes the dimeric form via a scorpion-like structure

Nuclear receptors (NRs) are a family of ligand-dependent transcription factors activated by lipophilic compounds. NRs share a common structure comprising three domains: a variable N-terminal domain (NTD), a highly conserved globular DNA-binding domain and a ligand-binding domain. There are numerous papers describing the molecular details of the latter two globular domains. However, very little is known about the structure-function relationship of the NTD, especially as an intrinsically disordered fragment of NRs that may influence the molecular properties and, in turn, the function of globular domains. Here, we investigated whether and how an intrinsically disordered NTD consisting of 58 amino acid residues affects the functions of the globular domains of the Ultraspiracle protein from Helicoverpa armigera (HaUsp). The role of the NTD was examined for two well-known and easily testable NR functions, i.e., interactions with specific DNA sequences and dimerization. Electrophoretic mobility shift assays showed that the intrinsically disordered NTD influences the interaction of HaUsp with specific DNA sequences, apparently by destabilization of HaUsp-DNA complexes. On the other hand, multi-angle light scattering and sedimentation velocity analytical ultracentrifugation revealed that the NTD acts as a structural element that stabilizes HaUsp homodimers. Molecular models based on small-angle X-ray scattering indicate that the intrinsically disordered NTD may exert its effects on the tested HaUsp functions by forming an unexpected scorpion-like structure, in which the NTD bends towards the ligand-binding domain in each subunit of the HaUsp homodimer. This structure may be crucial for specific NTD-dependent regulation of the functions of globular domains in NRs.

Involvement of methoprene-tolerant (Met) in the determination of the final body size in Leptinotarsa decemlineata (Say) larvae

In the tobacco hornworm Manduca sexta, juvenile hormone (JH) is critical for the control of species-specific size. However, whether the basic helix-loop-helix/Per-Arnt-Sim domain receptor methoprene-tolerant (Met) is involved remains unconfirmed. In the present paper, we found that RNA interference (RNAi)-aided knockdown of Met gene (LdMet) lowered the larval and pupal fresh weights and shortened the larval development period in the Colorado potato beetle Leptinotarsa decemlineata. Dietary introduction of JH into the LdMet RNAi larvae rescued neither the decreased weights nor the reduced development phase, even though JH ingestion by control larvae extended developmental time and caused large pupae. Moreover, the transcript levels of five genes involved in prothoracicotropic hormone and cap 'n' collar isoform C/Kelch-like ECH associated protein 1 pathways were upregulated in the LdMet silenced larvae. Ecdysteroidogenesis was thereby activated; 20-hydroxyecdysone (20E) titer was increased; and 20E signaling pathway was elicited in the LdMet RNAi larvae. Therefore, JH, acting through its receptor Met, inhibits PTTH production and release before the attainment of critical weight. Once the critical weight is reached, JH production and release are averted; and the hemolymph JH is removed. The elimination of JH allows the brain to release PTTH. PTTH subsequently stimulates ecdysteroid biosynthesis and release to start larval-pupal transition in L. decemlineata.

A New Role for Estrogen Receptor α in Cell Proliferation and Cancer: Activating the Anticipatory Unfolded Protein Response

Cells react to a variety of stresses, including accumulation of unfolded or misfolded protein, by activating the endoplasmic reticulum (EnR) stress sensor, the unfolded protein response (UPR). The UPR is highly conserved and plays a key role in the maintenance of protein folding quality control and homeostasis. In contrast to the classical reactive mode of UPR activation, recent studies describe a hormone-activated anticipatory UPR. In this pathway, mitogenic hormones, such as estrogen (E₂), epidermal growth factor, and vascular endothelial growth factor rapidly activate the UPR in anticipation of a future need for increased protein folding capacity upon cell proliferation. Here, we focus on this recently unveiled pathway of E₂-estrogen receptor α (ERα) action. Notably, rapid activation of the anticipatory UPR pathway is essential for subsequent activation of the E₂-ERα regulated transcription program. Moreover, activation of the UPR at diagnosis is a powerful prognostic marker in ERα positive breast cancer. Furthermore, in cells containing ERα mutations that confer estrogen independence and are common in metastatic breast cancer, the UPR is constitutively activated and linked to antiestrogen resistance. Lethal ERα-dependent hyperactivation of the anticipatory UPR represents a promising therapeutic approach exploited by a new class of small molecule ERα biomodulator.

The steroid hormone 20-hydroxyecdysone upregulates calcium release-activated calcium channel modulator 1 expression to induce apoptosis in the midgut of Helicoverpa armigera

Animal steroid hormones stimulate extracellular Ca²⁺ influx into cells; however, the mechanism remains unclear. In this study, we determined that the Ca²⁺ influx induced by steroid hormone 20-hydroxyecdysone (20E) is mediated by the calcium release-activated calcium channel modulator 1 (CRACM1/Orai1). The Orai1 mRNA is highly expressed during midgut programmed cell death in the lepidopteran insect Helicoverpa armigera. 20E upregulated the expression of Orai1 in H. armigera larvae and in an epidermal cell line (HaEpi). Knockdown of Orai1 in HaEpi cells blocked 20E-induced Ca²⁺ influx, and the inhibitor of inositol 1, 4, 5-trisphosphate receptor (IP₃R) Xestospongin (XeC) blocked 20E-induced Ca²⁺ influx, suggesting that 20E, via Orai1, induces stored-operated Ca²⁺ influx. Orai1 interacts with stromal interaction molecule 1(Stim1) to exert its function in 20E-induced Ca²⁺ influx. 20E promotes Orai1 aggregation through G-protein-coupled receptors, phospholipase C gamma 1, and Stim1. Knockdown of Orai1 in the HaEpi cell line repressed apoptosis and maintained autophagy under 20E regulation. Knockdown of Orai1 in larvae delayed pupation, repressed midgut apoptosis, maintained the midgut in an autophagic state, and repressed 20E-pathway gene expression. These results revealed that steroid hormone 20E, via Orai1, induces Ca²⁺ influx to promote the transition of midgut from autophagy to apoptosis.

Protein kinase C delta phosphorylates ecdysone receptor B1 to promote gene expression and apoptosis under 20-hydroxyecdysone regulation

The nuclear receptor EcRB1, which is activated by the insect steroid hormone 20-hydroxyecdysone (20E), is reportedly phosphorylated by a protein kinase after 20E induction. However, the protein kinase has not been identified, and the significance of EcRB1 phosphorylation is unclear. In this study, we identified a protein kinase C δ (PKCδ) isoform (the E isoform) that phosphorylates EcRB1 in the lepidopteran Helicoverpa armigera, a serious agricultural pest worldwide, to promote apoptotic gene expression and apoptosis during metamorphosis. Through activation of the EcRB1/USP1 transcription complex by 20E, PKCδ expression was up-regulated in several tissues during the metamorphic stage. Knockdown of PKCδ caused failure to transition from larvae to pupae, prevented tissues from undergoing programmed cell death (PCD), and down-regulated the expression of the transcription factor Brz-7 and the apoptosis executors caspase-3 and caspase-6 The threonine residue at position 1343 of PKCδ was phosphorylated and was critical for its proapoptotic function. Overexpression of the PKCδ catalytic domain was localized to the nuclei in HaEpi cells, which increased caspase-3 activity and apoptosis. PKCδ directly phosphorylated a threonine residue at position 468 in the amino acid sequence of EcRB1. The phosphorylation of EcRB1 was critical for its heterodimeric interaction with the USP1 protein and for binding to the ecdysone response element. The data suggested that 20E up-regulates PKCδ expression to regulate EcRB1 phosphorylation for EcRB1/USP1 transcription complex formation, apoptotic gene transcription, and apoptosis.

C-type lectin interacting with β-integrin enhances hemocytic encapsulation in the cotton bollworm, Helicoverpa armigera

The encapsulation reaction in invertebrates is analogous to granuloma formation in vertebrates, and this reaction is severely compromised when ecdysone signaling is blocked. However, the molecular mechanism underlying the encapsulation reaction and its regulation by ecdysone remains obscure. In our previous study, we found that the C-type lectin HaCTL3, from the cotton bollworm Helicoverpa armigera, is involved in anti-bacterial immune response, acting as a pattern recognition receptor (PRR). In the current study, we demonstrate that HaCTL3 is involved in defense against parasites and directly binds to the surface of nematodes. Our in vitro and in vivo studies indicate that HaCTL3 enhances hemocytic encapsulation and melanization, whereas H. armigera β-integrin (Haβ-integrin), located on the surface of hemocytes, participates in encapsulation. Additionally, co-immunoprecipitation experiments reveal HaCTL3 interacts with Haβ-integrin, and knockdown of Haβ-integrin leads to reduced encapsulation of HaCTL3-coated beads. These results indicate that Haβ-integrin serves as a hemocytic receptor of HaCTL3 during the encapsulation reaction. Furthermore, we demonstrate that 20-hydroxyecdysone (20E) treatment dramatically induces the expression of HaCTL3, and knockdown of the 20E receptor (EcR)/ultraspiracle (USP), abrogates this response. Overall, this study provides the first evidence of the presence of a hemocytic receptor (Haβ-integrin), that interacts with the PRR HaCTL3 to facilitate encapsulation reaction in insects and demonstrates the regulation of this process by the steroid hormone ecdysone.

Peptide microarray profiling identifies phospholipase C gamma 1 (PLC-γ1) as a potential target for t(8;21) AML

The t(8;21) (q22;q22) chromosomal translocation is one of the most frequent genetic alterations in acute myeloid leukemia (AML) which has a need for improved therapeutic strategies. We found PLC-γ1 as one of the highest phosphorylated peptides in t(8;21) AML samples compared to NBM or CN-AML in our previous peptide microarray. PLC-γ1 is known to play a role in cancer progression, however, the impact of PLC-γ1 in AML is currently unknown. Therefore, we aimed to study the functional role of PLC-γ1 by investigating the cellular growth, survival and its underlying mechanism in t(8;21) AML.

In this study, PLC-γ1 expression was significantly higher in t(8;21) AML compared to other karyotypes. The PLC-γ1 protein expression was suppressed in AML1-ETO knock down cells indicating that it might induce kasumi-1 cell death. ShRNA-mediated PLC-γ1 knockdown in kasumi-1 cells significantly blocked cell growth, induced apoptosis and cell cycle arrest which was explained by the increased activation of apoptotic related and cell cycle regulatory protein expressions. Gene expression array analysis showed the up-regulation of apoptotic and DNA damage response genes together with the downregulation of cell growth, proliferation and differentiation genes in the PLC-γ1 suppressed kasumi-1 cells, consistent with the observed phenotypic effects. Importantly, PLC-γ1 suppressed kasumi-1 cells showed higher chemosensitivity to the chemotherapeutic drug treatments and lower cell proliferation upon hypoxic stress.

Taken together, these in vitro finding strongly support an important role for PLC-γ1 in the survival of t(8;21) AML mimicking kasumi-1 cells and identify PLC-γ1 as a potential therapeutic target for t(8;21) AML treatment.

WITHDRAWN: C-type lectin interacting with β-integrin enhances hemocytic encapsulation in the cotton bollworm, Helicoverpa armigera

This article has been withdrawn at the request of the editor and publisher. The publisher regrets that an error occurred which led to the premature publication of this paper. This error bears no reflection on the article or its authors. The publisher apologizes to the authors and the readers for this unfortunate error. The article was subsequently accepted and published and can be viewed here: https://doi.org/10.1016/j.ibmb.2017.05.005 The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

The steroid hormone 20-hydroxyecdysone promotes switching from autophagy to apoptosis by increasing intracellular calcium levels

Autophagy regulates cell survival (or cell death in several cases), whereas apoptosis regulates cell death. However, the relationship between autophagy and apoptosis and the regulative mechanism is unclear. We report that steroid hormone 20-hydroxyecdysone (20E) promotes switching from autophagy to apoptosis by increasing intracellular calcium levels in the midgut of the lepidopteran insect Helicoverpa armigera. Autophagy and apoptosis sequentially occurred during midgut programmed cell death under 20E regulation, in which lower concentrations of 20E induced microtubule-associated protein 1 light chain 3-phosphatidylethanolamine (LC3-II, also known as autophagy-related gene 8, ATG8) expression and autophagy. High concentrations of 20E induced cleavage of ATG5 to NtATG5 and pro-caspase-3 to active caspase-3, which led to a switch from autophagy to apoptosis. Blocking autophagy by knockdown of ATG5, ATG7, or ATG12, or with the autophagy inhibitor 3-methyladenine, inhibited 20E-induced autophagy and apoptosis. Blocking apoptosis by using the apoptosis inhibitor Ac-DEVD-CHO did not prevent 20E-induced autophagy, suggesting that apoptosis relies on autophagy. ATG5 knockdown resulted in abnormal pupation and delayed pupation time. High concentrations of 20E induced high levels of intracellular Ca²⁺, NtATG5, and active caspase-3, which mediated the switch from autophagy to apoptosis. Blocking 20E-mediated increase of cellular Ca²⁺ caused a decrease of NtATG5 and active caspase-3 and repressed the transformation from autophagy to apoptosis, thereby promoting cell survival. 20E induces an increase in the concentration of intracellular Ca²⁺, thereby switching autophagic cell survival to apoptotic cell death.

Interplay between steroid hormone activation of the unfolded protein response and nuclear receptor action

To identify new pathways of estrogen action and novel estrogen receptor α (ERα) biomodulators, we performed high throughput screening and used follow on assays and bioinformatics to identify small molecule ERα inhibitors with a novel mode of action. These studies led to identification of rapid extranuclear activation of the endoplasmic reticulum stress sensor, the unfolded protein response (UPR), as a new pathway of estrogen-ERα action. Moreover, increasing evidence indicates that the mechanism underlying anticipatory activation of the UPR is shared among steroid and peptide hormones and is conserved from insects to humans. It is likely that this newly unveiled extranuclear pathway is used by diverse mitogenic hormones to prepare cells for the increased protein folding load that will occur during subsequent cell proliferation. Demonstrating biological relevance, elevated expression of a UPR gene signature in ERα positive breast cancer is a powerful new prognostic marker tightly correlated with subsequent resistance to tamoxifen, tumor recurrence and poor survival. In addition, overexpression of epidermal growth factor receptor and HER2/neu is positively correlated with increased UPR activation in breast cancer. This review describes recent research that demonstrates the importance of anticipatory UPR activation in therapy resistant tumors and discusses a promising small molecule biomodulator that inhibits tumor growth by tuning this UPR signaling pathway.

Anticipatory UPR Activation: A Protective Pathway and Target in Cancer

The endoplasmic reticulum (EnR) stress sensor, the unfolded protein response (UPR), plays a key role in regulating intracellular protein homeostasis. The extensively studied reactive mode of UPR activation is characterized by unfolded protein, or other EnR stress, triggering UPR activation. Here we focus on the emerging anticipatory mode of UPR activation in which mitogenic steroid and peptide hormones and other effectors preactivate the UPR and anticipate a future need for increased protein folding capacity. Mild UPR activation in breast cancer can be protective and contributes to antiestrogen resistance. Hyperactivation of the anticipatory UPR pathway in cancer cells with a small molecule converts it from cytoprotective to cytotoxic, highlighting its potential as a therapeutic target in estrogen receptor-positive breast cancer.

The Steroid Hormone 20-Hydroxyecdysone Promotes the Cytoplasmic Localization of Yorkie to Suppress Cell Proliferation and Induce Apoptosis

The transcriptional co-activator Yki (Yorkie), a member of the Hippo pathway, regulates cell proliferation or apoptosis, depending on its nuclear or cytoplasmic location. However, the upstream factors regulating the subcellular localization of Yki are unclear. We found that the steroid hormone 20-hydroxyecdysone (20E) induces phosphorylation of Yki, causing it to remain in the cytoplasm, where it promotes apoptosis in the midgut of the lepidopteran insect Helicoverpa armigera Yki is expressed in various tissues, with an increase in the epidermis and midgut during early metamorphic molting. Yki is localized mainly in the nucleus of feeding larval midgut cells but is mainly localized in the cytoplasm of metamorphic molting larval midgut cells. The knockdown of Yki in the feeding larvae promotes larval-pupal transition, midgut programmed cell death, and repressed IAP1 (inhibitor of apoptosis 1) expression. Knockdown of Yki in the epidermal cell line (HaEpi) induced increased activation of Caspase3/7. Overexpressed Yki in HaEpi cells was mainly localized in the nucleus and induced cell proliferation. 20E promotes the cytoplasmic localization of Yki, reducing the expression of the IAP1, resulting in apoptosis. 20E promotes cytoplasmic retention of Yki by increasing Yki phosphorylation levels and promoting the interaction between Yki and the adaptor protein 14-3-3-ϵ. This regulation of Yki suppresses cell proliferation and induces cell apoptosis.

The Steroid Hormone 20-Hydroxyecdysone Enhances Gene Transcription through the cAMP Response Element-binding Protein (CREB) Signaling Pathway

Animal steroid hormones regulate gene transcription through genomic pathways by binding to nuclear receptors. These steroid hormones also rapidly increase intracellular calcium and cyclic adenosine monophosphate (cAMP) levels and activate the protein kinase C (PKC) and protein kinase A (PKA) nongenomic pathways. However, the function and mechanism of the nongenomic pathways of the steroid hormones are unclear, and the relationship between the PKC and PKA pathways is also unclear. We propose that the steroid hormone 20-hydroxyecdysone (20E) activates the PKA pathway to enhance 20E-induced gene transcription in the lepidopteran insect Helicoverpa armigera The expression of the catalytic subunit 1 of PKA (PKAC1) increased during metamorphosis, and PKAC1 knockdown blocked pupation and repressed 20E-responsive gene expression. 20E regulated PKAC1 phosphorylation at threonine 200 and nuclear translocation through an ecdysone-responsive G-protein-coupled receptor 2. PKAC1 induced cAMP response element-binding protein (CREB) phosphorylation at serine 143, which bound to the cAMP response element on DNA to enhance 20E-responsive gene transcription. Through ecdysone-responsive G-protein-coupled receptor 2, 20E increased cAMP levels, which induced CREB PKA phosphorylation and 20E-responsive gene expression. This study demonstrates that the PKA/CREB pathway tightly and critically regulates 20E-induced gene transcription as well as its relationship with the 20E-induced PKC pathway.

Protein kinase C modulates transcriptional activation by the juvenile hormone receptor methoprene-tolerant

Juvenile hormone (JH) controls many biological events in insects by triggering dramatic changes in gene expression in target cells. The Methoprene-tolerant (MET) protein, an intracellular JH receptor, acts as a transcriptional regulator and binds to the promoters of tissue- and stage-specific JH target genes when JH is present. Our recent study has demonstrated that the transcriptional activation by MET is modulated by a membrane-initiated JH signaling pathway, involving phospholipase C (PLC) and calcium/calmodulin-dependent protein kinase II (CaMKII). Here we report that protein kinase C (PKC) is another essential intermediate of this pathway. PKC was activated by JH and this action was PLC-dependent. Inhibition of the PKC activity substantially weakened the JH-induced gene expression in mosquito cells. RNAi experiments indicated that several PKC isoforms were involved in the JH action during the post-emergence development of adult female mosquitoes. JH treatment considerably increased the binding of MET to the promoters of JH response genes in cultured mosquito abdomens that were collected from newly emerged female adults. The JH-induced DNA binding of MET was hindered when the abdomens were treated with a PKC inhibitor and JH. Therefore, the results suggest that PKC modulates the transactivation activity of MET by enhancing the binding of MET to JH response elements in the JH target genes. This mechanism may allow for variable and stage- and tissue-specific genomic responses to JH.

Anticipatory activation of the unfolded protein response by epidermal growth factor is required for immediate early gene expression and cell proliferation

The onco-protein epidermal growth factor (EGF) initiates a cascade that includes activation of the ERK and AKT signaling pathways and alters gene expression. We describe a new action of EGF-EGF receptor (EGFR), rapid anticipatory activation of the endoplasmic reticulum stress sensor, the unfolded protein response (UPR). Within 2 min, EGF elicits EGFR dependent activation of phospholipase C γ (PLCγ), producing inositol triphosphate (IP3), which binds to IP3 receptor (IP3R), opening the endoplasmic reticulum IP3R Ca(2+) channels, resulting in increased intracellular Ca(2+). This calcium release leads to transient and moderate activation of the IRE1α and ATF6α arms of the UPR, resulting in induction of BiP chaperone. Knockdown or inhibition of EGFR, PLCγ or IP3R blocks the increase in intracellular Ca(2+). While blocking the increase in intracellular Ca(2+) by locking the IP3R calcium channel with 2-APB had no effect on EGF activation of the ERK or AKT signaling pathways, it abolished the rapid EGF-mediated induction and repression of gene expression. Knockdown of ATF6α or XBP1, which regulate UPR-induced chaperone production, inhibited EGF stimulated cell proliferation. Supporting biological relevance, increased levels of EGF receptor during tumor progression were correlated with increased expression of the UPR gene signature. Anticipatory activation of the UPR is a new role for EGF. Since UPR activation occurs in <2 min, it is an initial cell response when EGF binds EGFR.

Virulent Diuraphis noxia Aphids Over-Express Calcium Signaling Proteins to Overcome Defenses of Aphid-Resistant Wheat Plants

The Russian wheat aphid, Diuraphis noxia, an invasive phytotoxic pest of wheat, Triticum aestivum, and barley, Hordeum vulgare, causes huge economic losses in Africa, South America, and North America. Most acceptable and ecologically beneficial aphid management strategies include selection and breeding of D. noxia-resistant varieties, and numerous D. noxia resistance genes have been identified in T. aestivum and H. vulgare. North American D. noxia biotype 1 is avirulent to T. aestivum varieties possessing Dn4 or Dn7 genes, while biotype 2 is virulent to Dn4 and avirulent to Dn7. The current investigation utilized next-generation RNAseq technology to reveal that biotype 2 over expresses proteins involved in calcium signaling, which activates phosphoinositide (PI) metabolism. Calcium signaling proteins comprised 36% of all transcripts identified in the two D. noxia biotypes. Depending on plant resistance gene-aphid biotype interaction, additional transcript groups included those involved in tissue growth; defense and stress response; zinc ion and related cofactor binding; and apoptosis. Activation of enzymes involved in PI metabolism by D. noxia biotype 2 aphids allows depletion of plant calcium that normally blocks aphid feeding sites in phloem sieve elements and enables successful, continuous feeding on plants resistant to avirulent biotype 1. Inhibition of the key enzyme phospholipase C significantly reduced biotype 2 salivation into phloem and phloem sap ingestion.

Cyclin-dependent kinase regulatory subunit 1 promotes cell proliferation by insulin regulation

Cyclin-dependent kinase regulatory subunit 1 (CKS1) helps regulate the cell cycle to increase cell number. However, the hormonal regulation on CKS1 expression is not well understood. We report that CKS1 is involved in the promotion of cell proliferation with insulin regulation in the lepidopteran insect Helicoverpa armigera. CKS1 is expressed in various tissues during the larval feeding stage. CKS1 knockdown results in larval death, body weight decrease, pupation time delay, and small-sized pupa formation. The underlying mechanism involves the blocking of cell proliferation and the repression of gene expression in the insulin pathway after CKS1 knockdown. CKS1 overexpression in the epidermal cell line results in cell proliferation. The N45 amino acid asparagine in the CKS domain is essential for the function of CKS in cell proliferation. CKS1 is upregulated by insulin via an insulin receptor, but is repressed by a high level of steroid hormone 20-hydroxyecdysone (20E). Results suggest that CKS1 promotes cell proliferation and body growth in coordination with the regulatory actions of insulin and steroid hormone 20E.

Juvenile hormone-activated phospholipase C pathway enhances transcriptional activation by the methoprene-tolerant protein

Juvenile hormone (JH) is a key regulator of a wide diversity of developmental and physiological events in insects. Although the intracellular JH receptor methoprene-tolerant protein (MET) functions in the nucleus as a transcriptional activator for specific JH-regulated genes, some JH responses are mediated by signaling pathways that are initiated by proteins associated with plasma membrane. It is unknown whether the JH-regulated gene expression depends on the membrane-mediated signal transduction. In Aedes aegypti mosquitoes, we found that JH activated the phospholipase C (PLC) pathway and quickly increased the levels of inositol 1,4,5-trisphosphate, diacylglycerol, and intracellular calcium, leading to activation and autophosphorylation of calcium/calmodulin-dependent protein kinase II (CaMKII). When abdomens from newly emerged mosquitoes were cultured in vitro, the JH-activated gene expression was repressed substantially if specific inhibitors of PLC or CaMKII were added to the medium together with JH. In newly emerged female mosquitoes, RNAi-mediated depletion of PLC or CaMKII considerably reduced the expression of JH-responsive genes, including the Krüppel homolog 1 gene (AaKr-h1) and the early trypsin gene (AaET). JH-induced loading of MET to the promoters of AaKr-h1 and AaET was weakened drastically when either PLC or CaMKII was inactivated in the cultured tissues. Therefore, the results suggest that the membrane-initiated signaling pathway modifies the DNA-binding activity of MET via phosphorylation and thus facilitates the genomic responses to JH. In summary, this study reveals an interplay of genomic and nongenomic signaling mechanisms of JH.

G-protein-coupled receptor controls steroid hormone signaling in cell membrane

G-protein-coupled receptors (GPCRs) are involved in animal steroid hormone signaling, but their mechanism is unclear. In this research, we report that a GPCR called ErGPCR-2 controls steroid hormone 20-hydroxyecdysone (20E) signaling in the cell membrane of the lepidopteran insect Helicoverpa armigera. ErGPCR-2 was highly expressed during molting and metamorphosis. 20E, via ErGPCR-2, regulated rapid intracellular calcium increase, protein phosphorylation, gene transcription, and insect metamorphosis. ErGPCR-2 was located in the cell surface and was internalized by 20E induction. GPCR kinase 2 participated in 20E-induced ErGPCR-2 phosphorylation and internalization. The internalized ErGPCR-2 was degraded by proteases to desensitize 20E signaling. ErGPCR-2 knockdown suppressed the entrance of 20E analog [(3)H] ponasterone A ([(3)H]Pon A) into the cells. ErGPCR-2 overexpression or blocking of ErGPCR-2 internalization increased the entrance of [(3)H]Pon A into the cells. However, ErGPCR-2 did not bind to [(3)H]Pon A. Results suggest that ErGPCR-2 transmits steroid hormone 20E signaling and controls 20E entrance into cells in the cell membrane.

The steroid hormone 20-hydroxyecdysone via nongenomic pathway activates Ca2+/calmodulin-dependent protein kinase II to regulate gene expression

The steroid hormone 20-hydroxyecdysone (20E) triggers calcium signaling pathway to regulate 20E response gene expression, but the mechanism underlying this process remains unclear. We propose that the 20E-induced phosphorylation of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) serves an important function in 20E response gene transcription in the lepidopteran insect Helicoverpa armigera. CaMKII showed increased expression and phosphorylation during metamorphosis. 20E elevated CaMKII phosphorylation. However, the G protein-coupled receptor (GPCR) and ryanodine receptor inhibitor suramin, the phospholipase C inhibitor U73122, and the inositol 1,4,5-triphosphate receptor inhibitor xestospongin C suppressed 20E-induced CaMKII phosphorylation. Two ecdysone-responsible GPCRs and Gαq protein were involved in 20E-induced CaMKII phosphorylation by RNA interference analysis. 20E regulated CaMKII threonine phosphorylation at amino acid 290, thereby inducing CaMKII nuclear translocation. CaMKII knockdown by dsCaMKII injection into the larvae prevented the occurrence of larval-pupal transition and suppressed 20E response gene expression. CaMKII phosphorylation and nuclear translocation maintained USP1 lysine acetylation at amino acid 303 by inducing histone deacetylase 3 phosphorylation and nuclear export. The lysine acetylation of USP1 was necessary for the interaction of USP1 with EcRB1 and their binding to the ecdysone response element. Results suggest that 20E (via GPCR activation and calcium signaling) activates CaMKII phosphorylation and nuclear translocation, which regulate USP1 lysine acetylation to form an EcRB1-USP1 complex for 20E response gene transcription.

β-Arrestin1 interacts with G protein-coupled receptor to desensitize signaling of the steroid hormone 20-hydroxyecdysone in the lepidopteran insect Helicoverpa armigera

The steroid hormone 20-hydroxyecdysone (20E) plays a critical role in insect development, particularly in larval molting and larval-pupal transition. Studies have indicated that 20E transmits its signal via a G protein-coupled receptor (GPCR)-mediated non-genomic pathway before a genomic pathway is initiated. However, the mechanism by which a 20E signal is desensitized remains unclear. We proposed that β-arrestin1 interacts with ecdysone-responsible GPCR (ErGPCR1) to desensitize a 20E signal in the lepidopteran insect Helicoverpa armigera. Results showed that β-arrestin1 was highly expressed in various tissues during metamorphosis. β-Arrestin1 knockdown by RNA interference in larvae caused advanced pupation and a larval-pupal chimera. The mRNA levels of 20E-response genes were increased after β-arrestin1 was knocked down but were decreased after β-arrestin1 was overexpressed. 20E induced the migration of β-arrestin1 from the cytosol to the cytoplasmic membrane to interact with ErGPCR1. The inhibitors suramin and chelerythrine chloride repressed 20E-induced β-arrestin1 phosphorylation and membrane migration. With ErGPCR1, 20E regulated β-arrestin1 phosphorylation on serines at positions 170 and 234. The double mutation of the amino acids Ser170 and Ser234 to asparagine inhibited phosphorylation and membrane migration of β-arrestin1 in 20E induction. Therefore, 20E via ErGPCR1 and PKC signaling induces β-arrestin1 phosphorylation; phosphorylated β-arrestin1 migrates to the cytoplasmic membrane to interact with ErGPCR1 to block 20E signaling via a feedback mechanism.

Heat shock protein 90 maintains the stability and function of transcription factor Broad Z7 by interacting with its Broad-Complex-Tramtrack-Bric-a-brac domain

Heat shock protein 90 (Hsp90) is a highly conserved chaperone protein that interacts with various client proteins to mediate their folding and stability. The Broad-Complex-Tramtrack-Bric-a-brac (BTB) domain, also known as poxvirus and zinc finger (POZ) domain, exists widely in different proteins and is highly conserved. However, the stability mechanism of BTB domain-containing proteins has not been fully understood. Co-immunoprecipitation and a protein pull-down assay were performed to investigate the interaction between Hsp90 and the transcription factor Broad isoform Z7 (BrZ7) in vivo and in vitro. The middle domain of Hsp90 directly associated with the BTB domain of BrZ7. The Hsp90 inhibitor 17-(Allylamino)-17-demethoxygeldanamycin (17-AAG) interrupted the interaction between Hsp90 and BrZ7 and decreased the protein level of BrZ7 but did not affect the mRNA level of BrZ7. The addition of the proteasome inhibitor peptide aldehyde Cbz-leu-leu leucinal suppressed the 17-AAG-induced degradation of BrZ7. BTB domain deletion and 17-AAG treatment resulted in inhibition of BrZ7 function in gene expression in the 20-hydroxyecdysone and juvenile hormone pathways. These results reveal that the middle domain of Hsp90 associates with the BTB domain of BrZ7 to prevent BrZ7 degradation and maintain BrZ7 function in gene expression in the lepidopteran insect Helicoverpa armigera.

Nuclear import of transcription factor BR-C is mediated by its interaction with RACK1

The transcription factor Broad Complex (BR-C) is an early ecdysone response gene in insects and contains two types of domains: two zinc finger domains for the activation of gene transcription and a Bric-a-brac/Tramtrack/Broad complex (BTB) domain for protein-protein interaction. Although the mechanism of zinc finger-mediated gene transcription is well studied, the partners interacting with the BTB domain of BR-C has not been elucidated until now. Here, we performed a yeast two-hybrid screen using the BTB domain of silkworm BR-C as bait and identified the receptor for activated C-kinase 1 (RACK1), a scaffolding/anchoring protein, as the novel partner capable of interacting with BR-C. The interaction between BR-C and RACK1 was further confirmed by far-western blotting and pull-down assays. Importantly, the disruption of this interaction, via RNAi against the endogenous RACK1 gene or deletion of the BTB domain, abolished the nuclear import of BR-C in BmN4 cells. In addition, RNAi against the endogenous PKC gene as well as phosphorylation-deficient mutation of the predicted PKC phosphorylation sites at either Ser373 or Thr406 in BR-C phenocopied RACK1 RNAi and altered the nuclear localization of BR-C. However, when BTB domain was deleted, phosphorylation mimics of either Ser373 or Thr406 had no effect on the nuclear import of BR-C. Moreover, mutating the PKC phosphorylation sites at Ser373 and Thr406 or deleting the BTB domain significantly decreased the transcriptional activation of a BR-C target gene. Given that RACK1 is necessary for recruiting PKC to close and phosphorylate target proteins, we suggest that the PKC-mediated phosphorylation and nuclear import of BR-C is determined by its interaction with RACK1. This novel finding will be helpful for further deciphering the mechanism underlying the role of BR-C proteins during insect development.

G-protein αq participates in the steroid hormone 20-hydroxyecdysone nongenomic signal transduction

The nuclear receptor-mediated genomic pathways of the animal steroid hormones are well known. However, the cell membrane receptor-mediated nongenomic pathways of the animal steroid hormones are little understood. In this study, we report the participation of a G-protein alpha q (Gαq)(1) subunit in the 20E nongenomic pathway in the cell membrane and regulating gene expression during molting and metamorphosis in a lepidopteran insect, Helicoverpa armigera. 20E-induced phosphorylation of Gαq was detected using two-dimensional electrophoresis techniques. Knockdown of Gαq by injecting double-stranded RNA suppressed the development of larvae, delayed metamorphosis, and inhibited 20E-induced gene expression. Gαq was distributed throughout the cell, and migrated toward the plasma membrane upon 20E induction. Gαq was necessary in the 20E-induced intracellular Ca(2+) release and extracellular Ca(2+) influx. The protein kinase C (PKC) inhibitor could repress 20E-induced phosphorylation of cyclin-dependent kinase 10 (CDK10) and transcription factor ultraspiracle (USP1). PKC inhibitor could repress the Gαq phosphorylation and membrane trafficking. These results suggest that Gαq participates in 20E signaling in the cell membrane at the pre-genomic stage by modulating the increase of the intracellular Ca(2+) and phosphorylation of CDK10 and USP1 in 20E transcription complex to regulate gene transcription.

Juvenile hormone prevents 20-hydroxyecdysone-induced metamorphosis by regulating the phosphorylation of a newly identified broad protein

The steroid hormone 20-hydroxyecdysone (20E) initiates insect molting and metamorphosis. By contrast, juvenile hormone (JH) prevents metamorphosis. However, the mechanism by which JH inhibits metamorphosis remains unclear. In this study, we propose that JH induces the phosphorylation of Broad isoform Z7 (BrZ7), a newly identified protein, to inhibit 20E-mediated metamorphosis in the lepidopteran insect Helicoverpa armigera. The knockdown of BrZ7 in larvae inhibited metamorphosis by repressing the expression of the 20E response gene. BrZ7 was weakly expressed and phosphorylated during larval growth but highly expressed and non-phosphorylated during metamorphosis. JH regulated the rapid phosphorylation of BrZ7 via a G-protein-coupled receptor-, phospholipase C-, and protein kinase C-triggered pathway. The phosphorylated BrZ7 bound to the 5'-regulatory region of calponin to regulate its expression in the JH pathway. Exogenous JH induced BrZ7 phosphorylation to prevent metamorphosis by suppressing 20E-related gene transcription. JH promoted non-phosphorylated calponin interacting with ultraspiracle protein to activate the JH pathway and antagonize the 20E pathway. This study reveals one of the possible mechanisms by which JH counteracts 20E-regulated metamorphosis by inducing the phosphorylation of BrZ7.