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Calcium destabilises Drosophila cactus protein and dephosphorylates the dorsal transcription factor
Abstract:
The Drosophila cactus and dorsal proteins are required for the development of embryonic dorso-ventral polarity and probably also for the innate immune response of the insect. Like their mammalian counterparts (the cytoplasmic anchor protein I kappa B and the rel/NF kappa B transcription factors) cactus and dorsal are regulated at the level of nuclear localisation. We showed previously that increased intra-cellular calcium levels induced by the ionophore ionomycin can activate dorsal/cactus complexes in the Drosophila cell line SL2. In order to study further the activation of dorsal/cactus complexes by calcium, we have prepared a cell line (SLDL) in which dorsal is expressed constitutively. In this paper we show that in SLDL cells ionomycin induces a rapid destruction of cactus and dephosphorylation of dorsal. These results suggest a role for the protein phosphatase calcineurin in calcium mediated activation of dorsal/cactus complexes. They also indicate that in the resting cell constitutive phosphorylation of dorsal is in equilibrium with calcium dependent dephosphorylation.
Insights
Calcium activates Drosophila
Area of Science:
- Molecular Biology
- Developmental Biology
- Immunology
Background:
- The Drosophila cactus and dorsal proteins regulate embryonic development and innate immunity.
- These proteins function similarly to mammalian IκB and NF-κB, with regulation at the nuclear localization level.
- Previous studies showed calcium ionophore ionomycin activates dorsal/cactus complexes in SL2 cells.
Purpose of the Study:
- To further investigate calcium-mediated activation of dorsal/cactus complexes.
- To characterize the effects of calcium on cactus and dorsal in a constitutively expressing dorsal cell line.
Main Methods:
- Generation of a Drosophila cell line (SLDL) with constitutive dorsal expression.
- Treatment of SLDL cells with the calcium ionophore ionomycin.
- Analysis of cactus protein destruction and dorsal protein dephosphorylation.
Main Results:
- Ionomycin treatment rapidly induced cactus destruction in SLDL cells.
- Ionomycin treatment led to dephosphorylation of dorsal in SLDL cells.
- These findings suggest calcineurin's involvement in calcium-mediated activation.
Conclusions:
- Calcium-dependent dephosphorylation of dorsal occurs in resting cells.
- The protein phosphatase calcineurin likely plays a role in calcium-mediated dorsal/cactus complex activation.
- These findings provide insights into the regulation of the dorsal/cactus pathway.