Specific Calcineurin Isoforms Are Involved in Drosophila Toll Immune Signaling

Abstract

Because excessive or inadequate responses can be detrimental, immune responses to infection require appropriate regulation. Networks of signaling pathways establish versatility of immune responses. Drosophila melanogaster is a powerful model organism for dissecting conserved innate immune responses to infection. For example, the Toll pathway, which promotes activation of NF-κB transcription factors Dorsal/Dorsal-related immune factor (Dif), was first identified in Drosophila. Together with the IMD pathway, acting upstream of NF-κB transcription factor Relish, these pathways constitute a central immune signaling network. Inputs in these pathways contribute to specific and appropriate responses to microbial insults. Relish activity during infection is modulated by Ca2+-dependent serine/threonine phosphatase calcineurin, an important target of immunosuppressants in transplantation biology. Only one of the three Drosophila calcineurin isoforms, calcineurin A1, acts on Relish during infection. However, it is not known whether there is a role for calcineurin in Dorsal/Dif immune signaling. In this article, we demonstrate involvement of specific calcineurin isoforms, protein phosphatase at 14D (Pp2B-14D)/calcineurin A at 14F (CanA-14F), in Toll-mediated immune signaling. These isoforms do not affect IMD signaling. In cell culture, pharmacological inhibition of calcineurin or RNA interference against homologous calcineurin isoforms Pp2B-14D/CanA-14F, but not against isoform calcineurin A1, decreased Toll-dependent Dorsal/Dif activity. A Pp2B-14D gain-of-function transgene promoted Dorsal nuclear translocation and Dorsal/Dif activity. In vivo, Pp2B-14D/CanA-14F RNA interference attenuated the Dorsal/Dif-dependent response to infection without affecting the Relish-dependent response. Altogether, these data identify a novel input, calcineurin, in Toll immune signaling and demonstrate involvement of specific calcineurin isoforms in Drosophila NF-κB signaling.

Calcineurin-Modulated Antimicrobial Peptide Expression Is Required for the Development of Helicoverpa armigera

“…These results provide evidence for the first time that HaCAN can activate relish through the IMD pathway to regulate the expression of cecropin D, attacin, and gloverin under gram-negative bacteria infection. Similar results were also found in Drosophila , in which CAN acted on relish during infection (Li and Dijkers, 2015).…”

“…Besides, Drosophila CAN has also been identified to play a role in immune response. When Drosophila were infected with gram-negative bacteria, CAN activity increased (Li and Dijkers, 2015). This promoted the product of relish, a key transcription factor of the immune deficiency (IMD) pathway in the innate immunity, which finally induces antimicrobial gene expression (Dijkers and O’Farrell, 2007; Li and Dijkers, 2015).…”

Lithium-Responsive Seizure-Like Hyperexcitability Is Caused by a Mutation in theDrosophilaVoltage-Gated Sodium Channel Geneparalytic

“…Furthermore, one of the three calcineurin isoforms, calcineurin A at 14F ( CanA-14F ) was upregulated in Shu . CanA-14F , along with the other two calcineurin genes in Drosophila , has been shown to play a role in innate immune signaling (Dijkers and O’Farrell, 2007; Li and Dijkers, 2015). Upregulation of immune gene expression was also observed in two seizure-prone para knock-in mutants, para DS and para GEFS+ .…”

β-Arrestins Negatively Regulate the Toll Pathway in Shrimp by Preventing Dorsal Translocation and Inhibiting Dorsal Transcriptional Activity

“…Gprk2 interacts with Cactus in S2 cells but is not involved in Cactus degradation; the detailed mechanism remains to be investigated. A recent study showed that specific calcineurin isoforms are also involved in Drosophila Toll immune signaling as positive regulators (11).…”