FOXA transcriptional factor modulates insect susceptibility to Bacillus thuringiensis Cry1Ac toxin by regulating the expression of toxin-receptor ABCC2 and ABCC3 genes

• Published in: Insect biochemistry and molecular biology Vol. 88; pp. 1 - 11
• Main Authors: Li, Jianghuai, Ma, Yuemin, Yuan, Wanli, Xiao, Yutao, Liu, Chenxi, Wang, Jia, Peng, Jianxin, Peng, Rong, Soberón, Mario, Bravo, Alejandra, Yang, Yongbo, Liu, Kaiyu
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-09-2017
• Subjects: Animals; ATP binding cassette; Bacillus thuringiensis; Bacterial Proteins; Endotoxins; Forkhead Transcription Factors - metabolism; FOXA; Gene Expression Regulation; Hemolysin Proteins; Insecticide Resistance; Larva - metabolism; Moths - metabolism; Multidrug Resistance-Associated Proteins - genetics; Multidrug Resistance-Associated Proteins - metabolism; Promoter Regions, Genetic; RNA Interference; Sequence Analysis, DNA; Sf9 Cells; Spodoptera; Toxin receptor; Transcription factor; FOXA; Transcription factor; ATP binding cassette; Bacillus thuringiensis; Toxin receptor
• ISSN: 0965-1748; 1879-0240
• DOI: 10.1016/j.ibmb.2017.07.004

Cry toxins produced by Bacillus thuringiensis (Bt) are insecticidal proteins widely used in insect control. Recently, it was shown that ATP-binding cassette transporter proteins (ABC) such as ABCC2, ABCC3, ABCG1 and ABCA2 are implicated in the insecticidal action of Cry toxins as putative receptors. However, the transcriptional regulators involved in the expression of ABC transporter genes remain unknown. Sequence analysis of promoter regions of ABCC2 gene from Helicoverpa armigera and ABCC3 gene from Spodoptera litura Sl-HP cultured cells, revealed the potential participation of Forkhead box protein A (FOXA), a transcription factor that regulates the expression of genes through remodeling chromatin. To determine if FOXA was involved in regulating expression of ABCC2 and ABCC3 genes, the expression of FOXA, ABCC2 and ABCC3 was compared in Sl-HP cells that are sensitive to Cry1Ac toxin with those in S. frugiperda Sf9 cells that are not sensitive to the toxin. Expression levels of those genes were significantly higher in Sl-HP than in Sf9 cells. Transient expression of FOXA in Sf9 cells activated ABCC2 and ABCC3 transcription, which directly correlated with enhanced Cry1Ac-susceptibility in these cells. Silencing of FOXA gene expression by RNAi in H. armigera larvae resulted in a decreased expression of ABCC2 and ABCC3 without affecting expression of other Cry toxin receptor genes such as alkaline phosphatase, aminopeptidase or cadherin. Silencing of FOXA gene expression also resulted in a Cry1Ac-tolerant phenotype since lower mortality and higher pupation rate were observed in diet containing Cry1Ac protoxin in comparison with the control group. These results demonstrate that FOXA up-regulates expression of the Cry1Ac-toxin receptor ABCC2 and ABCC3 genes, and that lower FOXA expression correlates with tolerance to Cry toxin in cell lines and in lepidopteran larvae.
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•The promoters of ABCC2 and ABCC3 have putative FOXA-binding sites in Lepidoptera.•FOXA binds to chromosomes.•FOXA activates ABCC2 and ABCC3 promoters in cell lines and larval midguts.•Expression of ABCC2 and ABCC3 increases susceptibility of insect cells to Cry1Ac toxin.•Down regulation of FOXA in larvae results in reduced expression of ABCC2 and ABCC3 genes and in tolerance to Cry1Ac toxin.