Functional Interaction between Cytochrome P450 and UDP-Glucuronosyltransferase on the Endoplasmic Reticulum Membrane: One of Post-translational Factors Which Possibly Contributes to Their Inter-Individual Differences

Emerging role of the crosstalk between gut microbiota and liver metabolome of subterranean herbivores in response to toxic plants

Plant secondary metabolites (PSMs) are a defense mechanism against herbivores, which in turn use detoxification metabolism to process ingested and absorbed PSMs. The feeding environment can cause changes in liver metabolism patterns and the gut microbiota. Here, we compared gut microbiota and liver metabolome to investigate the response mechanism of plateau zokors (Eospalax baileyi) to toxic plant Stellera chamaejasme (SC) in non-SC and SC grassland (-SCG and +SCG). Our results indicated that exposure to SC in the -SCG population increased liver inflammatory markers including prostaglandin (PG) in the Arachidonic acid pathway, while exposure to SC in the +SCG population exhibited a significant downregulation of PGs. Secondary bile acids were significantly downregulated in +SCG plateau zokors after SC treatment. Of note, the microbial taxa Veillonella in the -SCG group was significantly correlated with liver inflammation markers, while Clostridium innocum in the +SCG group had a significant positive correlation with secondary bile acids. The increase in bile acids and PGs can lead to liver inflammatory reactions, suggesting that +SCG plateau zokors may mitigate the toxicity of SC plants by reducing liver inflammatory markers including PGs and secondary bile acids, thereby avoiding liver damage. This provides new insight into mechanisms of toxicity by PSMs and counter-mechanisms for toxin tolerance by herbivores.

Functional characterization of CYP1 enzymes: Complex formation, membrane localization and function

CYP1A1, CYP1A2, and CYP1B1 have a high degree of sequence similarity, similar substrate selectivities and induction characteristics. However, experiments suggest that there are significant differences in their quaternary structures and function. The goal of this study was to characterize the CYP1 proteins regarding their ability to form protein-protein complexes, lipid microdomain localization, and ultimately function. This was accomplished by examining (1) substrate metabolism of the CYP1s as a function of NADPH-cytochrome P450 reductase (POR) concentration, and (2) quaternary structure, using bioluminescence resonance energy transfer (BRET). Both CYP1As were able to form BRET-detectable homomeric complexes, which was not observed with CYP1B1. When activities were measured as a function of [POR], CYP1A1 and CYP1B1 showed a hyperbolic response, consistent with mass-action binding; however, CYP1A2 produced a sigmoidal response, suggesting that the homomeric complex affected its function. Differences were observed in their ability to form heteromeric complexes. Whereas CYP1B1 and CYP1A1 formed a complex, neither the CYP1A1/CYP1A2 nor the CYP1B1/CYP1A2 pair formed BRET-detectable complexes. These proteins also differed in their lipid microdomain localization, with CYP1A2 and CYP1B1 residing in ordered membranes, and CYP1A1 in the disordered lipid regions. Taken together, despite their sequence similarities, there are substantial differences in quaternary structures and microdomain localization that can influence enzymatic activities. As these proteins exist in the endoplasmic reticulum with other ER-resident proteins, the P450s need to be considered as part of multi-enzyme systems rather than simply monomeric proteins interacting with their redox partners.

Comparative transcriptomes reveal geographic differences in the ability of the liver of plateau zokors (Eospalax baileyi) to respond and adapt to toxic plants

BACKGROUND

Environmental changes are expected to intensify in the future. The invasion of toxic plants under environmental changes may change herbivore feeding environments. Herbivores living long-term in toxic plant-feeding environments will inevitably ingest plant secondary metabolites (PSMs), and under different feeding environments are likely to have unique protection mechanisms that support improved adaptation to PSMs in their habitat. We aimed to compare different subterranean herbivore population responses and adaptations to toxic plants to unveil their feeding challenges.

RESULTS

Here, we investigated the adaptive capacity of the liver in two geographically separated populations of plateau zokors (Eospalax baileyi) before and after exposure to the toxic plant Stellera chamaejasme (SC), at the organ, biochemical, and transcriptomic levels. The results showed no significant liver granules or inflammatory reactions in the Tianzhu (TZ) population after the SC treatment. The transaminase level in the TZ population was significantly lower than that in the Luqu population. Transcriptome analysis revealed that the TZ population exhibited interactions with other detoxification metabolic pathways by oxytocin pathway-associated genes, including diacylglycerol lipase alpha (Dagla), calcium/calmodulin dependent protein kinase II Alpha (Camk2a), and CD38 molecule (Cd38). The phase II process of liver drug metabolism increased to promote the rate of metabolism. We found that alternative splicing (AS) and the expression of the cyclin D (Ccnd1) gene interact-a TZ population hallmark-reduced liver inflammatory responses.

CONCLUSION

Our study supports the detoxification limitation hypothesis that differences in liver detoxification metabolism gene expression and AS are potential factors in herbivore adaptation to PSMs and may be a strategy of different herbivore populations to improve toxic plant adaptability.

The Influence of Lipid Microdomain Heterogeneity on Protein-Protein Interactions: Proteomic Analysis of Co-Immunoprecipitated Binding Partners of P450 1A2 and P450 3A in Rat Liver Microsomes

Liver cytochrome P450s (CYPs) of the endoplasmic reticulum (ER) are involved in the metabolism of exogenous and endogenous chemicals. The ER is not uniform, but possesses ordered lipid microdomains containing higher levels of saturated fatty acids, sphingomyelin, and cholesterol and disordered regions containing higher levels of polyunsaturated fatty acid chains. The various forms of drug-metabolizing P450s partition to either the ordered or disordered lipid microdomains with different degrees of specificity. P450s readily form complexes with ER-resident proteins, including other forms of P450. This study aims to ascertain whether lipid microdomain localization influences protein-P450 interactions in rat liver microsomes. Thus, liver microsomes were co-immunoprecipitated with CYP1A2-specific and CYP3A-specific antibodies, and the co-immunoprecipitating proteins were identified by liquid chromatography mass spectrometry proteomic analysis. These two P450s preferentially partition to ordered and disordered microdomains, respectively. More than 100 proteins were co-immunoprecipitated with each P450. Segregation of proteins into different microdomains did not preclude their interaction. However, CYP3A interacted broadly with proteins from ordered microdomains, whereas CYP1A2 reacted with a limited subset of these proteins. This is consistent with the concept of lipid raft heterogeneity and may indicate that CYP1A2 is targeted to a specific type of lipid raft. Although many of the interacting proteins for both P450s were other-drug metabolizing enzymes, other interactions were also evident. The consistent CYP3A binding partners were predominantly involved in phase I/II drug metabolism; however, CYP1A2 interacted not only with xenobiotic metabolizing enzymes, but also with enzymes involved in diverse cellular responses such as ER stress and protein folding. SIGNIFICANCE STATEMENT: This work describes the protein interactomes in rat liver microsomes of two important cytochromes P450s (CYP1A2 and CYP3A) in drug metabolism and describes the relationship of the interacting proteins to lipid microdomain distribution.

CYP6DW3 Metabolizes Imidacloprid to Imidacloprid-urea in Whitefly (Bemisia tabaci)

Bemisia tabaci has developed high resistance to many insecticides and causes substantial agricultural and economic losses annually. The insecticide resistance of whitefly has been widely reported in previous studies; however, the underlying mechanism remains little known. In this study, we cloned two P450 genes: CYP6DW3 and CYP6DW5v1; these genes were markedly overexpressed in imidacloprid-resistant whitefly populations compared with susceptible populations, and knockdown of these genes decreased the imidacloprid resistance of whitefly. Moreover, heterologous expression of whitefly P450 genes in SF9 cells and metabolic studies showed that the CYP6DW3 protein could metabolize 14.11% imidacloprid and produced imidacloprid-urea in vitro. Collectively, the expression levels of CYP6DW3 and CYP6DW5v1 are positively correlated with imidacloprid resistance in B. tabaci. Our study further reveals that cytochrome P450 enzymes affect the physiological activities related to resistance in insects, which helps scholars more deeply understand the resistance mechanism, and contributes to the development of integrated pest management framework.

Use of a Baculovirus-Mammalian Cell Expression-System for Expression of Drug-Metabolizing Enzymes: Optimization of Infection With a Focus on Cytochrome P450 3A4

Heterologous expression systems are important for analyzing the effects of genetic factors including single nucleotide polymorphisms on the functions of drug-metabolizing enzymes. In this study, we focused on a baculovirus-mammalian cell (Bac-Mam) expression system as a safer and more efficient approach for this purpose. The baculovirus-insect cell expression system is widely utilized in large-scale protein expression. Baculovirus has been shown to also infect certain mammalian cells, although the virus only replicates in insect cells. With this knowledge, baculovirus is now being applied in a mammalian expression system called the Bac-Mam system wherein a gene-modified baculovirus is used whose promotor is replaced with one that can function in mammalian cells. We subcloned open-reading frames of cytochrome P450 3A4 (CYP3A4), UDP-glucuronosyltransferase (UGT) 1A1, and UGT2B7 into a transfer plasmid for the Bac-Mam system, and prepared recombinant Bac-Mam virus. The obtained virus was amplified in insect Sf9 cells and used to infect mammalian COS-1 cells. Expression of CYP3A4, UGT1A1, and UGT2B7 in COS-1 cell homogenates were confirmed by immunoblotting. Optimum infection conditions including the amount of Bac-Mam virus, culture days before collection, and concentration of sodium butyrate, an enhancer of viral-transduction were determined by monitoring CYP3A4 expression. Expressed CYP3A4 showed appropriate activity without supplying hemin/5-aminolevulinic acid or co-expressing with NADPH-cytochrome P450 reductase. Further, we compared gene transfer efficiency between the Bac-Mam system and an established method using recombinant plasmid and transfection reagent. Our results indicate that the Bac-Mam system can be applied to introduce drug-metabolizing enzyme genes into mammalian cells that are widely used in drug metabolism research. The expressed enzymes are expected to undergo appropriate post-translational modification as they are in mammalian bodies. The Bac-Mam system may thus accelerate pharmacogenetics and pharmacogenomics research.