Molecular cloning and expression profiles of the acyl-CoA-binding protein gene from the cotton bollworm Helicoverpa armigera

An entomopathogenic fungus exploits its host humoral antibacterial immunity to minimize bacterial competition in the hemolymph

BACKGROUND

The insect hemolymph (blood-equivalent fluid), composed of a large number of hemocytes (blood cells) and a variety of soluble immune effectors, is hostile for pathogens including fungi. In order to survive in the insect hemocoel (body cavity), the entomopathogenic fungus (EPF) has evolved two classical coping strategies, namely evasion and suppression of the host immune reactions. However, it remains unclear whether EPF has other ways of coping with host immunity.

RESULTS

In this study, we demonstrated that Metarhizium rileyi (an EPF) infection by injection of blastospores into the hemocoel enhanced the plasma antibacterial activity of cotton bollworm (Helicoverpa armigera), which was partially due to the enhanced expression of antimicrobial peptides (AMPs). The early stage of M. rileyi infection induced the translocation of gut bacteria into the hemocoel, where they were subsequently cleared due to the enhanced plasma antibacterial activity. Further, we showed that the enhanced plasma antibacterial activity and AMP expression were attributable to M. rileyi but not the invasive gut bacteria (opportunistic bacteria). Elevated ecdysone (major steroid hormone in insects) levels in the hemolymph at 48 h post-M. rileyi infection might contribute to the enhanced expression of AMPs. The fungus-elicited AMPs, such as cecropin 3 or lebocin, exhibited potent inhibitory activity against the opportunistic bacteria but not against hyphal bodies. In addition, the opportunistic bacteria competed with hyphal bodies for amino acid nutrients.

CONCLUSIONS

M. rileyi infection induced the translocation of gut bacteria, and then the fungi activated and exploited its host humoral antibacterial immunity to eliminate opportunistic bacteria, preventing them from competing for nutrients in the hemolymph. Unlike the classical strategies, EPF utilizes to evade or suppress host immunity, our findings reveal a novel strategy of interaction between EPF and host immunity. Video Abstract.

DNA G-quadruplex structure participates in regulation of lipid metabolism through acyl-CoA binding protein

G-quadruplex structure (G4) is a type of DNA secondary structure that widely exists in the genomes of many organisms. G4s are believed to participate in multiple biological processes. Acyl-CoA binding protein (ACBP), a ubiquitously expressed and highly conserved protein in eukaryotic cells, plays important roles in lipid metabolism by transporting and protecting acyl-CoA esters. Here, we report the functional identification of a G4 in the promoter of the ACBP gene in silkworm and human cancer cells. We found that G4 exists as a conserved element in the promoters of ACBP genes in invertebrates and vertebrates. The BmACBP G4 bound with G4-binding protein LARK regulated BmACBP transcription, which was blocked by the G4 stabilizer pyridostatin (PDS) and G4 antisense oligonucleotides. PDS treatment with fifth instar silkworm larvae decreased the BmACBP expression and triacylglycerides (TAG) level, resulting in reductions in fat body mass, body size and weight and growth and metamorphic rates. PDS treatment and knocking out of the HsACBP G4 in human hepatic adenocarcinoma HepG2 cells inhibited the expression of HsACBP and decreased the TAG level and cell proliferation. Altogether, our findings suggest that G4 of the ACBP genes is involved in regulation of lipid metabolism processes in invertebrates and vertebrates.

Transcriptomic and proteomic analysis of the underlying mechanisms of digestion of triacylglycerols and phosphatides and absorption and fate of fatty acids along the midgut of Musca domestica

Most dietary lipids are triacylglycerols (TAGs) and phosphatides that are digested by TAG lipases and phospholipases (PLIPs), respectively, originating fatty acids (FA). The genome of Musca domestica has genes coding for phospholipases A1 (1PLIP), A2 (2PLIP), B (BPLIP), and acid lipases (ALIP), as for proteins involved in activation, binding, and metabolism of FA, which expression in the larval midgut was evaluated by RNA-seq. Some of the codified proteins were identified in midgut microvillar-enriched membrane by proteomics. 1PLIPs are the most expressed PLIPs, mainly in anterior midgut whereas 2PLIPs, and BPLIP in middle and posterior midgut, and ALIPs between middle and posterior regions. Absorption of FAs is putatively accomplished by proteins involved in FA activation (acyl-CoA synthetases) found in microvillar-enriched membrane preparations. Furthermore, FA uptake could be enhanced by proteins that bind FAs (FA-binding proteins) and its activated form (acyl-CoA binding proteins) mainly expressed in posterior midgut. Activated FAs could have different fates: synthesis of diacylglycerol (DAG) and TAG through monoacylglycerol and glycerol-3-phosphate pathways; synthesis of phosphatides; energy source by β-oxidation. Most genes coding for enzymes of those routes is expressed mainly at the end of posterior midgut. Data suggest that phosphatides are digested in anterior midgut by Md1PLIPs, releasing lysophosphatides that emulsify fats to be digested by MdALIPs in the middle and posterior midgut. Most resulting FAs is absorbed in the posterior midgut, where they follow the synthesis of DAG, TAG, and phosphatides or are oxidized along the midgut, mainly in highly metabolic middle and posterior midgut regions.

Expression of acyl-CoA-binding protein 5 from Rhodnius prolixus and its inhibition by RNA interference

The acyl-CoA-binding proteins (ACBP) act by regulating the availability of acyl-CoA in the cytoplasm and must have essential functions in lipid metabolism. The genome of the kissing-bug Rhodnius prolixus encodes five proteins of this family, but little is known about them. In this study we investigated the expression and function of RpACBP-5. Feeding induced RpACBP-5 gene expression in the posterior midgut, and an increase of about four times was observed two days after the blood meal. However, the amount of protein, which was only detected in this organ, did not change during digestion. The RpACBP-5 gene was also highly expressed in pre-vitellogenic and vitellogenic oocytes. Recombinant RpACBP-5 was shown to bind to acyl-CoA of different lengths, and it exhibited nanomolar affinity to lauroyl-CoA in an isothermal titration assay, indicating that RpACBP-5 is a functional ACBP. RpACBP-5 knockdown by RNA interference did not affect digestion, egg laying and hatching, survival, or accumulation of triacylglycerol in the fat body and oocytes. Similarly, double knockdown of RpACBP-1 and RpACBP-5 did not alter egg laying and hatching, survival, accumulation of triacylglycerol in the fat body and oocytes, or the neutral lipid composition of the posterior midgut or hemolymph. These results show that RpACBP-5 is a functional ACBP but indicate that the lack of a detectable phenotype in the knockdown insects may be a consequence of functional overlap of the proteins of the ACBP family found in the insect.

The ACBP gene family in Rhodnius prolixus: Expression, characterization and function of RpACBP-1

The acyl-CoA-binding proteins (ACBP) constitute a family of conserved proteins that bind acyl-CoA with high affinity and protect it from hydrolysis. Thus, ACBPs may have essential roles in basal cellular lipid metabolism. The genome of the insect Rhodnius prolixus encodes five ACBP genes similar to those described for other insect species. The qPCR analysis revealed that these genes have characteristic expression profiles in insect organs, suggesting that they have specific roles in insect physiology. Recombinant RpACBP-1 was able to bind acyl-CoA in an in vitro gel-shift assay. Moreover, heterologous RpACBP-1 expression in acb1Δ mutant yeast rescued the multi-lobed vacuole phenotype, indicating that RpACBP-1 acts as a bona fide acyl-CoA-binding protein. RpACBP-1 knockdown using RNAi caused triacylglycerol accumulation in the insect posterior midgut and a reduction in the number of deposited eggs. The amount of stored triacylglycerol was reduced in flight muscle, and the incorporation of fatty acids in cholesteryl esters was increased in the fat body. These results showed that RpACBP-1 participates in several lipid metabolism steps in R. prolixus.

Involvement of a pattern recognition receptor C-type lectin 7 in enhancing cellular encapsulation and melanization due to its carboxyl-terminal CRD domain in the cotton bollworm, Helicoverpa armigera

C-type lectins play important roles in innate immunity as pattern recognition receptors (PRRs). We have previously reported a novel C-type lectin HaCTL7 from the cotton bollworm (Helicoverpa armigera) which contains two carbohydrate-recognition domains (CRDs), namely N-terminal CRD1 and C-terminal CRD2. Interestingly, there are four but not six of conserved cysteine residues in CRD2 of HaCTL7, which is different from that of other dual CRD C-type lectins. In the current study, we expressed and purified recombinant HaCTL7 (rHaCTL7) as well as rCRD1 and rCRD2, and demonstrated that both rHaCTL7 and rCRD2, but not rCRD1, owned the agglutinate ability against both Gram-negative and Gram-positive bacteria in a calcium dependent manner. In addition, both rHaCTL7 and rCRD2, but not rCRD1, could bind to various bacteria, and enhanced haemocytes mediated encapsulation and melanization processes. HaCTL7 secreted from fat bodies is able to bind to granulocytes, plasmatocytes and oenocytoids, but not to spherulocytes. Recombinant HaCTL7 and rCRD2 are capable of binding to both granulocytes and oenocytoids, while rCRD1 can only bind to granulocytes. Our data suggest that as a PRR HaCTL7 enhances encapsulation and melanization likely through its C-terminal CRD2, but not N-terminal CRD1, which imply that the characteristic four cysteine structure of CRD2 plays key roles in innate immunity.

Molecular cloning and characterization of acyl-CoA binding protein (ACBP) gene from shrimp Penaeus monodon exposed to salinity stress

Acyl-CoA binding protein (ACBP), a protein present ubiquitously in wide range of organisms play significant role in transport of acyl groups for macromolecular biosynthesis involved in various functional and regulatory processes. In crustaceans, ACBP has functional role in growth, reproduction and temperature tolerance. In the present study, two suppression subtractive hybridization (SSH) cDNA libraries were performed using gut tissues of shrimp Penaeus monodon exposed to low (3 ppt) and high (55 ppt) salinity stress conditions. SSH library resulted in identification of differentially expressed genes that belonged to various functional classes such as the nucleic acid regulation and replication, defence proteins, allergen protein, signal transduction pathways, apoptosis, energy and metabolism, cell cycle regulation and hypothetical proteins. ACBP was identified as one of the differentially expressed gene in both the SSH libraries of shrimp P. monodon subjected to low and high salinity stress. The full-length cDNA of P. monodon ACBP gene was isolated and the sequence revealed 273 bp open reading frame encoding 90 amino acids with molecular mass of 10 kDa and pI 6.8. The ORF showed presence of four phosphorylation sites, with absence of signal peptide sequence and glycosylation sites. The deduced amino acid sequence of ACBP exhibited high sequence identity (92%) with ACBP class of protein identified from Fenneropenaeus chinensis. Real time PCR analysis of shrimps subjected to 3 ppt salinity conditions after 2 weeks revealed an increase in expression of ACBP transcripts, in the gut (28.08-folds), gills (11.71-folds) and in the muscle tissues (1.70-folds). Whereas, shrimps exposed to 55 ppt salinity conditions after 2 weeks exhibited increased ACBP transcript levels in the gut (11.95-folds), gills (1.052-folds) and muscle tissues (7.35-folds). The significant increase in expression levels of ACBP in various tissues of shrimps suggests a functional role of this gene in salinity stress tolerance and adaptation.

Involvement of low molecular mass soluble acyl-CoA-binding protein in seed oil biosynthesis

Acyl-CoA-binding protein (ACBP), a low molecular mass (m) (∼ 10 kDa) soluble protein ubiquitous in eukaryotes, plays an important housekeeping role in lipid metabolism by maintaining the intracellular acyl-CoA pool. ACBP is involved in lipid biosynthesis and transport, gene expression, and membrane biogenesis. In plants, low m ACBP and high m ACBPs participate in response mechanisms to biotic and abiotic factors, acyl-CoA transport in phloem, and biosynthesis of structural and storage lipids. In light of current research on the modification of seed oil, insight into mechanisms of substrate trafficking within lipid biosynthetic pathways is crucial for developing rational strategies for the production of specialty oils with the desired alterations in fatty acid composition. In this review, we summarize our knowledge of plant ACBPs with emphasis on the role of low m ACBP in seed oil biosynthesis, based on in vitro studies and analyses of transgenic plants. Future prospects and possible applications of low m ACBP in seed oil modification are discussed.

Serotonin regulates an acyl-CoA-binding protein (ACBP) gene expression in the midgut of Rhodnius prolixus

Acyl-CoA esters have many intracellular functions, acting as energy source, substrate for metabolic processes and taking part in cell signaling. The acyl-CoA-binding protein (ACBP), a highly conserved 10 kDa intracellular protein, binds long- and medium-chain acyl-CoA esters with very high affinity, directing them to specific metabolic routes and protecting them from hydrolysis. An ACBP gene sequence was identified in the genome of Rhodnius prolixus. This ACBP gene (RpACBP-1) was expressed in all analyzed tissues and quantitative PCR showed that expression was highest in posterior midgut. In this tissue, ACBP gene expression increased in the first day after blood meal ( approximately 10-fold) and then decreased to unfed levels in the seventh day after meal. Injection of serotonin (5-hydroxytryptamine; 5-HT), a neuroamine released in the hemolymph after the start of feeding, increased the expression of this gene in the midgut of unfed females, reaching levels similar to those observed in fed insects. This effect of injected 5-HT was inhibited by spiperone, an antagonist of 5-HT mammalian receptors, that was also able to block the physiological increase in RpACBP-1 expression observed after feeding. Injection of cholera toxin or dibutyryl-cAMP also resulted in the stimulation of this gene expression. These data reveal a transcriptional regulatory mechanism in R. prolixus, that is triggered by 5-HT. In this way, a novel role for 5-HT is proposed, as a regulator of ACBP gene expression and, consequently, taking part in the control of lipid metabolism.

A C-type lectin is involved in the innate immune response of Chinese white shrimp

C-type lectins may function as pattern-recognition receptors (PRRs) and play important roles in immune responses. In this work, a cDNA for a new C-type lectin, FcLec3, was obtained from Chinese white shrimp Fenneropenaeus chinensis using expressed sequence tag analysis and rapid amplification of the cDNA ends. FcLec3 contains an N-terminal signal peptide and a carbohydrate recognition domain (CRD). RT-PCR analysis showed that FcLec3 was mainly expressed in hepatopancreas and that the expression of FcLec3 was obviously up-regulated by Vibrio anguillarum or white spot syndrome virus (WSSV) challenge. Recombinant FcLec3 could agglutinate Gram-negative and -positive bacteria with the presence of calcium. A following agglutination inhibitory test indicated that FcLec3 could recognize muramic acid and peptidoglycan. Besides, pull-down assay showed that the recombinant protein could interact with VP28, one major envelope protein of WSSV. These results suggested that FcLec3 might function in the recognition of bacterial and viral pathogens in shrimp.