Toxicity of Cry1A toxins from Bacillus thuringiensis to CF1 cells does not involve activation of adenylate cyclase/PKA signaling pathway

• Published in: Insect biochemistry and molecular biology Vol. 80; pp. 21 - 31
• Main Authors: Portugal, Leivi, Muñóz-Garay, Carlos, Martínez de Castro, Diana L., Soberón, Mario, Bravo, Alejandra
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-01-2017
• Subjects: AC/PKA pathway; Adenylyl Cyclases - genetics; Adenylyl Cyclases - metabolism; Animals; Bacillus thuringiensis; Bacterial Proteins - toxicity; Cell Line; CF1 cell line; Choristoneura fumiferana; Cry toxins; Cyclic AMP-Dependent Protein Kinases - genetics; Cyclic AMP-Dependent Protein Kinases - metabolism; Endotoxins - toxicity; Hemolysin Proteins - toxicity; Insect Proteins - genetics; Insect Proteins - metabolism; Larva - drug effects; Larva - genetics; Larva - microbiology; MAP Kinase Signaling System; MAPK p38; Mechanism of action; Moths - drug effects; Moths - genetics; Moths - growth & development; Moths - microbiology; Signal Transduction; MAPK p38; CF1 cell line; AC; ALP; Bacillus thuringiensis; IBMX; PKA; HRP; Cry toxins; AC/PKA pathway; LC50; LDH; Bt; 3d-Cry; PMSF; FBS; SLO; ED50; Mechanism of action; APN; FSK; PFT
• ISSN: 0965-1748; 1879-0240
• DOI: 10.1016/j.ibmb.2016.11.004

Bacillus thuringiensis (Bt) bacteria produce Cry toxins that are able to kill insect pests. Different models explaining the mode of action of these toxins have been proposed. The pore formation model proposes that the toxin creates pores in the membrane of the larval midgut cells after interaction with different receptors such as cadherin, aminopeptidase N and alkaline phosphatase and that this pore formation activity is responsible for the toxicity of these proteins. The alternative model proposes that interaction with cadherin receptor triggers an intracellular cascade response involving protein G, adenylate cyclase (AC) and protein kinase A (PKA). In addition, it was shown that Cry toxins induce a defense response in the larvae involving the activation of mitogen-activated kinases such as MAPK p38 in different insect orders. Here we analyzed the mechanism of action of Cry1Ab and Cry1Ac toxins and a collection of mutants from these toxins in the insect cell line CF1 from Choristoneura fumiferana, that is naturally sensitive to these toxins. Our results show that both toxins induced permeability of K+ ions into the cells. The initial response after intoxication with Cry1Ab and Cry1Ac toxins involves the activation of a defense response that involves the phosphorylation of MAPK p38. Analysis of activation of PKA and AC activities indicated that the signal transduction involving PKA, AC and cAMP was not activated during Cry1Ab or Cry1Ac intoxication. In contrast we show that Cry1Ab and Cry1Ac activate apoptosis. These data indicate that Cry toxins can induce an apoptotic death response not related with AC/PKA activation. Since Cry1Ab and Cry1Ac toxins affected K+ ion permeability into the cells, and that mutant toxins affected in pore formation are not toxic to CF1, we propose that pore formation activity of the toxins is responsible of triggering cell death response in CF1cells.
[Display omitted]
•Cry1Ab and Cry1Ac toxins induced permeability of K+ ions into CF1 cells.•Initial response to Cry1A toxins involves activation of a defense response with phosphorylation of MAPK p38.•The AC/PKA signaling pathway is not involved in the toxicity of Cry1Ab or Cry1Ac to CF1 cells.•Cry1Ab and Cry1Ac toxins activate apoptosis in CF1.