Intracellular mobilization of Ca2+ by the insect steroid hormone 20-hydroxyecdysone during programmed cell death in silkworm anterior silk glands.
20-Hydroxyecdysone (20E) triggers programmed cell death (PCD) and regulates de novo gene expression in the anterior silk glands (ASGs) of the silkworm Bombyx mori. PCD is mediated via a nongenomic pathway that includes Ca2+ as a second messenger and the activation of protein kinase C/caspase-3-like protease; however, the steps leading to a concomitant buildup of intracellular Ca2+ are unknown. We employed pharmacological tools to identify the components of this pathway. ASGs were cultured in the presence of 1 microM 20E and one of the following inhibitors: a G-protein-coupled receptor (GPCR) inhibitor, a phospholipase C (PLC) inhibitor, an inositol 1,4,5-trisphosphate receptor (IP3R) antagonist, and an L- or T-type Ca2+ channel blocker. The T-type Ca2+ channel blocker inhibited 20E-induced nuclear and DNA fragmentation; in contrast, PCD was induced by 20E in Ca2+-free medium, indicating that the source of Ca2+ is an intracellular reservoir. The IP3R antagonist inhibited nuclear and DNA fragmentation, suggesting that the endoplasmic reticulum may be the Ca2+ source. Finally, the GPCR and PLC inhibitors effectively blocked nuclear and DNA fragmentation. Our results indicate that 20E increases the intracellular level of Ca2+ by activating IP3R, and that this effect may be brought about by the serial activation of GPCR, PLC, and IP3.
Manaboon
Manaporn
M
Division of Life Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa 920-1192, Japan. manaboon@stu.kanazawa-u.ac.jp
Iga
Masatoshi
M
Iwami
Masafumi
M
Sakurai
Sho
S
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D012831:Bombyx / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D053938:DNA Fragmentation; D004441:Ecdysterone / Q000378:metabolism*; D005088:Exocrine Glands / Q000378:metabolism; D007211:Indoles; D015290:Second Messenger Systems / Q000502:physiology*
D007211:Indoles; C007293:DAPI; D004441:Ecdysterone; D002118:Calcium