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Calnexin co-expression and the use of weaker promoters increase the expression of correctly assembled Shaker potassium channel in insect cells.

Voltage-gated potassium channels control the membrane potential of excitable cells. To understand their function, knowledge of their structure is essential. However, these channels are scarce in natural sources, and overexpression is necessary to generate material for structural studies. We have compared functional expression of the Drosophila Shaker H4 potassium channel in stable insect cell lines and in baculovirus-infected insect cells, using three different baculovirus promoters. Stable insect cell lines expressed correctly assembled channel, which was glycosylated and found predominantly at, or close to, the cell surface. In comparison, the majority of baculovirus-overexpressed Shaker was intracellular and incorrectly assembled. The proportion of functional Shaker increased, however, if the weaker basic protein promoter was used rather than the stronger p10 or polyhedrin promoters. In addition, co-expression of the molecular chaperone, calnexin, increased the quantity of correctly assembled channel protein, suggesting that calnexin can be used to increase the efficiency of channel expression in insect cells.

Animals↗

Comparison of the formation of N-alkylprotoporphyrin IX after interaction of porphyrinogenic xenobiotics with single cDNA-expressed human P450 enzymes in microsomes prepared from baculovirus-infected insect cells and human lymphoblastoid cell lines.

In a previous study using microsomes from human lymphoblastoid cell lines (HLCL) containing single cDNA-expressed human cytochrome P450 (P450) enzymes, human P450 enzymes were identified that are susceptible to mechanism-based inactivation by the porphyrinogenic xenobiotics, 3-[(arylthio)ethyl]sydnone (TTMS), 3,5-diethoxycarbonyl-1,4-dihydro-2,6-dimethyl-4-ethylpyridine (4-ethylDDC) and allylisopropylacetamide (AIA). In this study, we tested the hypothesis that N-alkylprotoporphyrin IX (N-alkylPP) formation following interaction of porphyrinogenic xenobiotics with single cDNA-expressed human P450 enzymes in microsomes from HLCL would occur only with P450 enzymes that had undergone mechanism-based inactivation. In a previous study, when 4-ethylDDC and NADPH interacted with human liver microsomes possessing elevated levels of CYP1A2 and 2C9, N-ethylprotoporphyrin IX (N-ethylPP) was not formed despite the fact that it was formed in microsomes from baculovirus-infected insect cell lines (BIICL) containing either CYP1A2 or 2C9. In this study, we tested the hypothesis that 4-ethylDDC underwent biotransformation by CYP3A4 present in human liver microsomes, diverting the xenobiotic from CYP1A2 and 2C9. Fluorometry was used to measure N-alkylPP formation following interaction of porphyrinogenic xenobiotics and NADPH with cDNA-expressed human P450 enzymes in microsomes from HLCL or BIICL. With TTMS and 4-ethylDDC but not with AIA, N-alkylPP formation was observed only with human P450 enzymes CYP2D6, 1A2, 3A4, or 2C9 in microsomes from HLCL, which had undergone mechanism-based inactivation. Microsomes from BIICL containing CYP3A4 were added to a mixture of NADPH, 4-ethylDDC, and microsomes from BIICL containing CYP1A2 and 2C9. The addition of CYP3A4 to CYP1A2 and 2C9 did not decrease N-ethylPP formation, providing no support for the hypothesis.

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Advancing insect research through cell line transcriptomics.

This review emphasizes the significance of insect cell lines in transcriptomic research, highlighting their role as vital tools for uncovering cellular and molecular mechanisms of insect physiology, immune responses, and adaptation to environmental stressors. Cell lines derived from tissues such as the midgut, fat body, nervous system, and reproductive organs enable researchers to examine gene expression changes in a controlled setting, making discoveries that are difficult to achieve through whole-organism studies. High-throughput sequencing and single-cell RNA sequencing (scRNA-seq) have identified genes linked to detoxification, stress response, development, and immune defense, offering valuable insights for future applications in agriculture, pest control, and biotechnology. To organize this information clearly, we have summarized key findings in a table, providing an accessible overview of each cell line's important roles in transcriptomic research. This method not only highlights the adaptability of insect cell lines in functional genomics but also underscores their usefulness as model systems in pest management, virology, and bioengineering. Through utilizing transcriptomics, insect cell lines continue to advance our understanding of insect biology and foster the development of innovative strategies for sustainable crop protection and biotechnological use.

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Interaction of Autographa californica nuclear polyhedrosis virus with two nonpermissive cell lines.

The interaction of Autographa californica nuclear polyhedrosis virus with two nonpermissive cell lines was investigated. The insect cell line, CP 169, and the Chinese hamster cell line, CHO-K1, were able to adsorb and engulf virus particles, but there was no evidence for viral replication in these cells based on virus growth titrations, electron microscopy, dot hybridization, and synthesis of viral induced proteins.

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Diversity of G proteins in Lepidopteran cell lines: partial sequences of six G protein alpha subunits.

The aim of this work was to sample the diversity of G protein alpha subunits in lepidopteran insect cell lines. Here we report the amplification by degenerate PCR of partial sequences representing six G protein alpha subunits from three different lepidopteran insect cell lines. Sequence comparisons with known G protein alpha subunits indicate that the Sf9, Ld and High Five cell lines each contain (at least) one Galpha(q)-like and one Galpha(i)-like Galpha subunit. All six PCR products are unique at the nucleotide level, but the translation products of the three Galpha q-like partial clones (Sf9-Galpha 1, Ld-Galpha 1, and Hi5-Galpha 1) are identical, as are the translation products of the three Galpha i-like partial clones (Sf9-Galpha 2, Ld-Galpha 2, and Hi5-Galpha 2). Both the Galpha(q)-like and Galpha(i)-like translation products are identical to known Galpha subunits from other Lepidoptera, are highly similar (88-98%) to Galpha subunits from other invertebrates including mosquitoes, fruit flies, lobsters, crabs, and snails, and are also highly similar (88-90%) to known mammalian Galpha subunits. Identification of G protein alpha subunits in lepidopteran cell lines will assist in host cell line selection when insect cell lines are used for the pharmacological analysis of human GPCRs.

Amino Acid Sequence↗

Intrinsic glycosylation potentials of insect cell cultures and insect larvae.

The glycosylation and subsequent processing of native and recombinant glycoproteins expressed in established insect cell lines and insect larvae were compared. The Spodoptera frugiperda (Sf21) and Trichoplusia ni (TN-368 and BTI-Tn-5B1-4) cell lines possessed several intrinsic glycoproteins that are modified with both N- and O-linked oligosaccharides. The N-linked oligosaccharides were identified as both the simple (high mannose) and complex (containing sialic acid) types. Similarly, the T. ni larvae also possessed intrinsic glycoproteins that were modified with O-linked and simple and complex N-linked oligosaccharides. Additionally, human placental, secreted alkaline phosphatase (SEAP) produced during replication of a recombinant baculovirus in T. ni larvae was modified with complex oligosaccharide having sialic acid linked alpha(2-6) to galactose.

Alkaline Phosphatase↗

Immunoreactivities for calcium signaling components and neural-like properties of a Colorado potato beetle cell line.

Of the approximately 400 described insect cell lines, only three are derived from beetles (Coleoptera), and none are neural in origin. The present work was undertaken to characterize further a new cell line, designated IPLB-CPB2, derived from eggs of the Colorado potato beetle, Leptinotarsa decimlineata. Indirect immunofluorescent studies reported here indicate that these cells express neurofilament (Nf)-like immunoreactivities to antibodies directed against mammalian Nf-Medium (MW 150,000) and a heavily phosphorylated form of Nf-Heavy (MW 200,000; detected using the axonal monoclonal antibody SMI 31). This appears to be the first report of neurofilament-like immunoreactivity in an arthropod. Immunofluorescent analyses also indicate that IPLB-CPB2 cells express an antigenic epitope characteristic of the mammalian type 1 inositol trisphosphate (IP3) receptor, the ryanodine receptor (RyR) (also termed calcium-induced calcium release receptor channel, or CICR) and the sarco(endo)plasmic reticulum Ca2+ pump (SERCA). Patch-clamp recordings indicate that some IPLB-CPB2 cells are capable of producing spontaneous action potentials, while others may be photosensitive. Taken together, the findings reported here suggest that IPLB-CPB2 cells are of neural origin and that they express the major receptor channels and pumps known to be localized in the ER of the cell, which are required for receptor-mediated calcium signaling. Thus, the IPLB-CPB2 cell line may prove to be an excellent model system for studies of insect neurobiology and calcium-based signal transduction.

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Isolation and analysis of a baculovirus vector that supports recombinant glycoprotein sialylation by SfSWT-1 cells cultured in serum-free medium.

The inability to sialylate recombinant glycoproteins is a critical limitation of the baculovirus-insect cell expression system. This limitation is due, at least in part, to the absence of detectable sialyltransferase activities and CMP-sialic acids in the insect cell lines routinely used as hosts in this system. SfSWT-1 is a transgenic insect cell line encoding five mammalian glycosyltransferases, including sialyltransferases, which can contribute to sialylation of recombinant glycoproteins expressed by baculovirus vectors. However, sialylation of recombinant glycoproteins requires culturing SfSWT-1 cells in the presence of fetal bovine serum or another exogenous source of sialic acid. To eliminate this requirement and extend the utility of SfSWT-1 cells, we have isolated a new baculovirus vector, AcSWT-7B, designed to express two mammalian enzymes that can convert N-acetylmannosamine to CMP-sialic acid during the early phase of infection. AcSWT-7B was also designed to express a model recombinant glycoprotein during the very late phase of infection. Characterization of this new baculovirus vector showed that it induced high levels of intracellular CMP-sialic acid and sialylation of the recombinant N-glycoprotein upon infection of SfSWT-1 cells cultured in serum-free medium supplemented with N-acetylmannosamine. In addition, co-infection of SfSWT-1 cells with AcSWT-7B plus a conventional baculovirus vector encoding human tissue plasminogen activator resulted in sialylation of this recombinant N-glycoprotein under the same culture conditions. These results demonstrate that AcSWT-7B can be used in two different ways to support recombinant N-glycoprotein sialylation by SfSWT-1 cells in serum-free medium. Thus, AcSWT-7B can be used to extend the utility of this previously described transgenic insect cell line for recombinant sialoglycoprotein production.

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Pyridalyl, a novel insecticide: potency and insecticidal selectivity.

Pyridalyl is an insecticide of a novel chemical class (unclassified insecticides). Toxicity of pyridalyl to two insect pest species, Spodoptera litura and Frankliniella occidentalis, an insect predator, Orius stringicollis, and a pollinator, Bombus terrestris, was evaluated in the laboratory. The insecticidal activity of pyridalyl against S. litura was evaluated using the leaf-dipping method. The potency of pyridalyl was highly effective against all development stages (2nd to 6th instar larvae) of S. litura. This compound was also evaluated against F. occidentalis using the direct spray method. For F. occidentalis, toxicity of pyridalyl was almost similar to that of acrinathrin, but greater than acrinathrin for adults. Then the toxicity of this product to the natural enemies, Orius stringicollis and the pollinating insect Bombus terrestris, was evaluated using the body-dipping method or direct spray method. No acute toxicity of this product was observed on these non-target insects. Moreover, the influence of pyridalyl to the nest of Bombus terrestris was evaluated using the direct spray to the inside of the nest. No apparent influence of this compound was observed by 21 days after treatment. The cytotoxicity of pyridalyl to the Sf9 insect cell line and the CHO-K1 mammalian cell line was evaluated using the trypan-blue exclusion method. High toxicity to the insect cell line, but almost no toxicity to the mammalian cell line, was observed. Thus, pyridalyl exhibited high selectivity in cytotoxicity between the insect and mammalian cell line as well as in insecticidal activity among insect species. We infer pyridalyl may be useful for IPM programs of greenhouse cultivation system.

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Distinct N-glycan fucosylation potentials of three lepidopteran cell lines.

The fucosyltransferase activities of three insect cell lines, MB-0503 (from Mamestra brassicae), BM-N (from Bombyx mori) and Sf-9 (from Spodoptera frugiperda), were investigated and compared with that of honeybee venom glands. Cell extracts and venom gland extracts were incubated with GDP-[14C]fucose and glycopeptides isolated from human IgG and from bovine fibrin. The labeled oligosaccharide products were released by peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase A, fluorescence marked with 2-aminopyridine and analyzed both by reversed-phase and size-fractionation HPLC. They were identified by their elution positions before and after exoglycosidase treatment in comparison with standard oligosaccharides. These experiments revealed distinct fucosylation potentials in the three cell lines tested. While MB-0503 cells, like honeybee venom glands, are able to transfer fucose into alpha 1-3 and alpha 1-6 linkage to the innermost N-acetylglucosamine, only alpha 1-6-fucosyl linkages were detected with BM-N and Sf-9 cells.

Animals↗

Topoisomerase II-independent doxorubicin-induced cytotoxicity in an extremely doxorubicin-resistant cell line.

Lepidopteran insect cells (TN-368) were found to be extremely resistant to the anthracycline, doxorubicin. They were approximately 400 fold more resistant to the cytotoxic effects of doxorubicin compared to a mammalian counterpart; V79 hamster lung fibroblast cells. Doxorubicin accumulated into TN-368 cells and bound to DNA in a similar fashion as the interaction of doxorubicin in V79 cells. However, no doxorubicin-induced stabilized DNA-topoisomerase II complexes could be demonstrated in TN-368 cells (even at the high concentrations of doxorubicin that resulted in cytotoxicity). Therefore, the lack of formation of this critical lesion may be the cause of the marked doxorubicin resistance noted in the TN-368 cells.

Animals↗

Expression of functional recombinant antibody molecules in insect cell expression systems.

Recombinant single-chain variable-fragment molecules (scFv) were constructed from a cell line expressing a monoclonal antibody against African cassava mosaic virus (ACMV) and expressed in Escherichia coli. DNA sequences that encoded the scFv were manipulated to allow scFv expression in insect cell lines. A recombinant baculovirus containing the scFv cDNA was constructed and large amounts of scFv were produced in each of three insect cell lines infected with the baculovirus. However, the scFv were not secreted into the medium by any of the cell lines despite the scFv having been linked to a honeybee melittin leader sequence. The same scFv cDNA construct was introduced into Drosophila DS2 cells and a stable recombinant cell line was obtained that produced scFv that was secreted into the medium. Culture medium containing the scFv was used directly in enzyme-linked immunosorbent assay (ELISA) tests to detect ACMV in plant tissues. Another construct that encoded the Ckappa domain of human IgG was fused to the C-terminus of the scFv that was produced and expressed in Drosophila cells. This scFv derivative also accumulated in the medium and was more active in ELISA than scFv lacking the Ckappa domain.

Animals↗

Improved glycosylation of a foreign protein by Tn-5B1-4 cells engineered to express mammalian glycosyltransferases.

The major advantages of using the baculovirus-insect cell system for recombinant protein production are its ability to produce large amounts of recombinant proteins and its ability to provide eucaryotic modifications, such as glycosylation. However, the glycans linked to recombinant glycoproteins produced by this system typically differ from those found on native mammalian products. This is an important problem because glycans on mammalian glycoproteins can influence their functions in many different ways. The inability of baculovirus-infected insect cells to produce glycans identical to those found on native mammalian glycoproteins is due, in part, to the absence of functional levels of certain glycosyltransferases in insect cells. Thus, the purpose of this study was to engineer these activities into Tn-5B1-4, an established insect cell line that is widely used as a host for baculovirus-mediated protein production. Expression plasmids were constructed in which cDNAs encoding mammalian beta1,4-galactosyltransferase and alpha2,6-sialyltransferase were placed under the transcriptional control of a baculovirus immediate early promoter. These plasmids were then used to isolate two different transgenic Tn-5B1-4 derivatives and the biological and biochemical properties of these cell lines were examined. The results show that both of the engineered insect cell lines have improved glycoprotein-processing capabilities, relative to the parental cell line.

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Comparison of cell line maintenance procedures on insect cells used for producing baculoviruses.

A gypsy moth cell line, IPLB-LdEIta, maintained under various conditions was tested for susceptibility to and productivity of two baculoviruses, the Autographa californica nucleopolyhedrovirus (AcMNPV) and Lymantria dispar nucleopolyhedrovirus (LdMNPV). The results suggest that cells maintained in serum-containing medium (modified TC100) were more susceptible (on the basis of titers in an endpoint assay) to LdMNPV than cells maintained in a serum-free medium (ExCell 400). Such a difference was not apparent with AcMNPV. Similarly, little difference existed in the proportion of cells containing occlusion bodies (OBs) a wk after inoculation with AcMNPV (i.e., the percent infected) in any LdEIta strains, although one combination of cells and medium (cells maintained in ExCell 400 but infected in TC100) showed a lower percent infection with LdMNPV. Even though the percentage of cells infected varied little, the number of OBs produced varied by 3 logs with AcMNPV and 11/2 logs with LdMNPV. In each case, cells normally grown in ExCell 400 and infected in the same medium produced the lowest number of OBs. However, productivity was improved when cells normally grown in ExCell 400 were infected in TC100. Even more interesting was that cells normally grown in TC100 produced more AcMNPV OBs when infected in ExCell 400 medium. This suggests that changing culture medium (regardless of the normal maintenance medium) can stimulate virus production. In addition to examining virus productivity in LdEIta cells in both serum-containing and serum-free media, I also tested a strain maintained at low temperature (17 degrees C) for over a yr. This maintenance protocol was not detrimental for LdMNPV productivity and was slightly stimulatory for production of AcMNPV.

Animals↗

Glycoproteins of nuclear polyhedrosis viruses.

The glycopeptides and glycoproteins of two nuclear polyhedrosis viruses (NPVs) grown in two lepidopteran insect cell lines were studied using Sephadex elution chromatography and polyacrylamide gel electrophoresis. No quantitative or qualitative differences were observed in the glycopeptide and glycoprotein patterns between the viruses grown in either cell line. However, both viruses synthesized a glycoprotein which was not observed in either insect cell line and may be virus-directed.

Animals↗

siRNA-directed silencing of transgene expressed in cultured insect cells.

RNA interference (RNAi) has emerged as a powerful tool to rapidly analyze gene functions in a wide variety of eukaryotic organisms as well as in cultured cell lines. We demonstrate here that RNAi can be applied to study the function of a transgene expressed in an insect cell line (Spodoptera frugiperda, Sf21). The aminopeptidase N gene (apn) targeted for silencing in the present study was isolated from the midgut of Spodoptera litura larvae and expressed in Sf21 cells using baculovirus expression system. The recombinant APN protein expressed at the surface of Sf21 cells was shown to interact with insecticidal crystal protein, Cry1C, by in vitro experiments. The exogenous addition/transfection of APN dsRNA or siRNA in the cultured cells resulted in partial/complete inhibition of expression of apn leading to the loss of toxin binding to the transgene expressing cells. These experiments highlighted the usefulness of RNAi as a tool to study the function of an expressed transgene in insect cell line and to study the specificity of receptor-ligand interaction.

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In vitro cultivation and antibiotic susceptibility of a Cytophaga-like intracellular symbiote isolated from the tick Ixodes scapularis.

A Cytophaga-like organism (CLO), isolated from the tick Ixodes scapularis (IsCLO), was adapted to growth in insect cell lines and its antibiotic sensitivity was tested. IsCLO were introduced to four insect cell lines, and their growth was measured by quantitative polymerase chain reaction. IsCLO propagated well in a mosquito cell line, AeAl-2, and caused cytopathic effects in host cells. A lepidopteran cell line, HZ-AM1, was also suitable for propagation of IsCLO and kept a steady state with bacterial growth. Using IsCLO-infected AeAl-2, antibiotics effective against the bacteria included ampicillin, chloramphenicol, penicillin-G, rifampicin, and tetracycline. These antibiotics will be useful for eliminating CLO from host arthropods, which is necessary for in vivo studies of the intracellular facultative symbiotes.

Animals↗