Description
Thapsigargin is a naturally occurring sesquiterpene lactone isolated from the umbelliferous plant Thapsia garganica. It is a non-competitive, cell permeable inhibitor of calcium transport by SERCAs (IC50 values are cell type-dependent and range from ~2-80 nM). This tumor promoter releases Ca2+ from intracellular stores by specifically inhibiting the endoplasmic reticulum Ca2+-ATPase; it does not directly affect plasma membrane Ca2+-ATPases, Ins 1,4,5-P3 production or protein kinase C activity. This effect is a result of emptying the intracellular calcium stores, which leads to a chain of events that causes apoptosis.
Chemical Properties
Thapsigargin (TG) is colourless film. It is extracted from the plant Thapsia garganica L. with methanol and purified by HPLC. TG is a tumor promoting plant sesquiterpene lactone extract with a unique biological activity as Ca2+ -ATPase inhibitors in animal cells. It is a skin irritant, a platelet activating, inflammatory and tumor promoting agent. TG is toxic and a possible carcinogen.
Uses
THAPSIGARGIN is a widely used inhibitor of the ubiquitous sarco-endoplasmic reticulum Ca(2+)-ATPases in mammalian cells. It acts as a potent, cell-permeable, IP3-independent intracellular calcium releaser that blocks the transient increase in intracellular Ca2+ induced by angiostatin and endostatin. It induces apoptosis by disrupting intracellular free Ca2+ levels.
Definition
ChEBI: Thapsigargin is an organic heterotricyclic compound that is a hexa-oxygenated 6,7-guaianolide isolated fron the roots of Thapsia garganica L., Apiaceae. A potent skin irritant, it is used in traditional medicine as a counter-irritant. Thapsigargin inhibits Ca(2+)-transporting ATPase mediated uptake of calcium ions into sarcoplasmic reticulum and is used in experimentation examining the impacts of increasing cytosolic calcium concentrations. It has a role as an EC 3.6.3.8 (Ca(2+)-transporting ATPase) inhibitor and a calcium channel blocker. It is a sesquiterpene lactone, an organic heterotricyclic compound and a butyrate ester.
Biochem/physiol Actions
Thapsigargin is an effective inhibitor of calcium ion pumps located on sarcoplasmic reticulum (SR) and endoplasmic reticulum (ER) microsomes of skeletal, cardiac, muscle and brain tissues. The inhibition of calcium ion pumps causes intracellular increase of calcium ion levels. It was found that thapsigargin at 100 nM concentration effectively inhibited the SR Ca2+- adenosine triphosphatase (ATPase) in cardiac and skeletal muscles. Thapsigargin was also reported to be effective in blocking autophagy by interfering with the autophagosome-lysosome fusion.
Mode of action
The actual mechanism of action of thapsigargin is thought actually to block calcium channels in an open conformation that results in excess calcium entry from outside the cell. Excess calcium activates DNAses and precipitates the natural death sequence of the cells.Scientists are now thinking of modifying thapsigargin in such a way thatit will kill prostate cells preferentially and will not penetrate healthy cells elsewhere in the body.At the same time, they are determining whether this drug can also induce cell death in breast cancer cells.
References
1) Treiman et al. (1998), A tool coming of age: thapsigargin as an inhibitor of sarco-endoplasmic reticulum Ca(2+)-ATPases; Trends Pharmacol. Sci., 19 131
2) Zhou et al. (2009), Autophagy-mediated insulin receptor down-regulation contributes to endoplasmic reticulum stress-induced insulin resistance; Mol. Pharmacol., 76 596
