Limits...
Timosaponin AIII is preferentially cytotoxic to tumor cells through inhibition of mTOR and induction of ER stress.

King FW, Fong S, Griffin C, Shoemaker M, Staub R, Zhang YL, Cohen I, Shtivelman E - PLoS ONE (2009)

Bottom Line: Analysis of the mechanisms of death induced by TAIII revealed activation of two distinct pro-apoptotic pathways: first, inhibition of mTORC1 manifested in much reduced phosphorylation of mTORC1 targets; second, induction of endoplasmic reticulum stress culminating in phosphorylation of eIF2alpha and activation of caspase 4.Inhibition of mTORC1 and induction of ER stress apparently contribute to the induction of the previously reported autophagic response in TAIII-treated cells.TAIII induced autophagy plays a protective role in TAIII induced death signaling, and failure to mount autophagic response is associated with heightened sensitivity to TAIII induced apoptosis.

View Article: PubMed Central - PubMed

Affiliation: BioNovo Inc, Emeryville, California, United States of America.

ABSTRACT
The aqueous extract of Anemarrhena asphodeloides (BN108) induces apoptosis in various cancer cell lines but is significantly less cytotoxic in non-transformed cells. Chemical fractionation of BN108 showed that its cytotoxicity is associated with timosaponins, steroidal saponins of coprostane type. Timosaponin BII (TBII) is a major saponin in BN108, but it shows little cytotoxicity. A much less abundant TAIII induces cell death in tumor cells but not in normal cells, reproducing the selectivity of the total extract BN108. Glycosidase treatment, by removing the extra sugar moiety in TBII, converts it to TAIII and confers cytotoxic activity. Analysis of the mechanisms of death induced by TAIII revealed activation of two distinct pro-apoptotic pathways: first, inhibition of mTORC1 manifested in much reduced phosphorylation of mTORC1 targets; second, induction of endoplasmic reticulum stress culminating in phosphorylation of eIF2alpha and activation of caspase 4. These pro-apoptotic pathways are activated by TAIII selectively in tumor cells but not in normal cells. Both pathways play a causative role in TAIII cytotoxicity, as restoration of either mTOR activity or relief of ER stress alone offer only partial protection from TAIII. Inhibition of mTORC1 and induction of ER stress apparently contribute to the induction of the previously reported autophagic response in TAIII-treated cells. TAIII induced autophagy plays a protective role in TAIII induced death signaling, and failure to mount autophagic response is associated with heightened sensitivity to TAIII induced apoptosis. The multiple death-promoting and apparently tumor-selective responses to TAIII, its ability to inhibit mTORC1, and the possibility of further enhancing its cytotoxicity by pharmacological inhibition of autophagy, make TAIII an attractive candidate for development as a cancer therapeutic agent.

Show MeSH

Related in: MedlinePlus

Autophagy induced by TAIII plays a protective role in cell death.A. Inhibition of autophagy augments apoptosis induced by TAIII in MDAMB231 and MCF10A cell lines, but not in BT474. Cells were pretreated for three hours with 20 µM of chloroquine (CQ) after which TAIII (4 µM for BT474, 5 µM for MM231 and 7.5 µM for MCF10A) was added for 24 hours. B. A cartoon illustrating the various cellular effects of BN108 and TAIII. The pathways induced selectively in cancer cells are shown in thicker lines.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2747272&req=5

pone-0007283-g006: Autophagy induced by TAIII plays a protective role in cell death.A. Inhibition of autophagy augments apoptosis induced by TAIII in MDAMB231 and MCF10A cell lines, but not in BT474. Cells were pretreated for three hours with 20 µM of chloroquine (CQ) after which TAIII (4 µM for BT474, 5 µM for MM231 and 7.5 µM for MCF10A) was added for 24 hours. B. A cartoon illustrating the various cellular effects of BN108 and TAIII. The pathways induced selectively in cancer cells are shown in thicker lines.

Mentions: Treatment of cells with TAIII in presence of autophagy inhibitor chloroquine revealed that autophagy plays different roles in TAIII induced responses. In the most sensitive cells, BT474, inhibition of autophagy did not affect the outcome of TAIII treatment, indicating that autophagy is either not induced or is not protective in these cells. However, inhibition of autophagy in MDAMB231 and particularly in the MCF10A cells lead to a significantly increased cell death in response to TAIII (Figure 6A). Autophagy also played a protective role in the TAIII induced apoptosis in a breast cancer line SKBr3 and, as previously reported, HeLa cells (not shown). Induction of autophagic responses was confirmed by following levels and distribution of GFP-LC3 in transfected MDAMB231 cells after treatment with TAIII, as well as Western blot analysis of LC3 cleavage (Figure S3). However, treatment of BT474 cells with TAIII has not affected distribution of the transfected GFP-LC3 (not shown) indicating that these cells do not develop autophagy in response to TAIII. We conclude that the previously reported induction of autophagy by TAIII [4] is protective in a variety of cells including the TAIII-resistant cells, and that lack of autophagic response to TAIII is associated with increased sensitivity to its pro-apoptotic effects.


Timosaponin AIII is preferentially cytotoxic to tumor cells through inhibition of mTOR and induction of ER stress.

King FW, Fong S, Griffin C, Shoemaker M, Staub R, Zhang YL, Cohen I, Shtivelman E - PLoS ONE (2009)

Autophagy induced by TAIII plays a protective role in cell death.A. Inhibition of autophagy augments apoptosis induced by TAIII in MDAMB231 and MCF10A cell lines, but not in BT474. Cells were pretreated for three hours with 20 µM of chloroquine (CQ) after which TAIII (4 µM for BT474, 5 µM for MM231 and 7.5 µM for MCF10A) was added for 24 hours. B. A cartoon illustrating the various cellular effects of BN108 and TAIII. The pathways induced selectively in cancer cells are shown in thicker lines.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2747272&req=5

pone-0007283-g006: Autophagy induced by TAIII plays a protective role in cell death.A. Inhibition of autophagy augments apoptosis induced by TAIII in MDAMB231 and MCF10A cell lines, but not in BT474. Cells were pretreated for three hours with 20 µM of chloroquine (CQ) after which TAIII (4 µM for BT474, 5 µM for MM231 and 7.5 µM for MCF10A) was added for 24 hours. B. A cartoon illustrating the various cellular effects of BN108 and TAIII. The pathways induced selectively in cancer cells are shown in thicker lines.
Mentions: Treatment of cells with TAIII in presence of autophagy inhibitor chloroquine revealed that autophagy plays different roles in TAIII induced responses. In the most sensitive cells, BT474, inhibition of autophagy did not affect the outcome of TAIII treatment, indicating that autophagy is either not induced or is not protective in these cells. However, inhibition of autophagy in MDAMB231 and particularly in the MCF10A cells lead to a significantly increased cell death in response to TAIII (Figure 6A). Autophagy also played a protective role in the TAIII induced apoptosis in a breast cancer line SKBr3 and, as previously reported, HeLa cells (not shown). Induction of autophagic responses was confirmed by following levels and distribution of GFP-LC3 in transfected MDAMB231 cells after treatment with TAIII, as well as Western blot analysis of LC3 cleavage (Figure S3). However, treatment of BT474 cells with TAIII has not affected distribution of the transfected GFP-LC3 (not shown) indicating that these cells do not develop autophagy in response to TAIII. We conclude that the previously reported induction of autophagy by TAIII [4] is protective in a variety of cells including the TAIII-resistant cells, and that lack of autophagic response to TAIII is associated with increased sensitivity to its pro-apoptotic effects.

Bottom Line: Analysis of the mechanisms of death induced by TAIII revealed activation of two distinct pro-apoptotic pathways: first, inhibition of mTORC1 manifested in much reduced phosphorylation of mTORC1 targets; second, induction of endoplasmic reticulum stress culminating in phosphorylation of eIF2alpha and activation of caspase 4.Inhibition of mTORC1 and induction of ER stress apparently contribute to the induction of the previously reported autophagic response in TAIII-treated cells.TAIII induced autophagy plays a protective role in TAIII induced death signaling, and failure to mount autophagic response is associated with heightened sensitivity to TAIII induced apoptosis.

View Article: PubMed Central - PubMed

Affiliation: BioNovo Inc, Emeryville, California, United States of America.

ABSTRACT
The aqueous extract of Anemarrhena asphodeloides (BN108) induces apoptosis in various cancer cell lines but is significantly less cytotoxic in non-transformed cells. Chemical fractionation of BN108 showed that its cytotoxicity is associated with timosaponins, steroidal saponins of coprostane type. Timosaponin BII (TBII) is a major saponin in BN108, but it shows little cytotoxicity. A much less abundant TAIII induces cell death in tumor cells but not in normal cells, reproducing the selectivity of the total extract BN108. Glycosidase treatment, by removing the extra sugar moiety in TBII, converts it to TAIII and confers cytotoxic activity. Analysis of the mechanisms of death induced by TAIII revealed activation of two distinct pro-apoptotic pathways: first, inhibition of mTORC1 manifested in much reduced phosphorylation of mTORC1 targets; second, induction of endoplasmic reticulum stress culminating in phosphorylation of eIF2alpha and activation of caspase 4. These pro-apoptotic pathways are activated by TAIII selectively in tumor cells but not in normal cells. Both pathways play a causative role in TAIII cytotoxicity, as restoration of either mTOR activity or relief of ER stress alone offer only partial protection from TAIII. Inhibition of mTORC1 and induction of ER stress apparently contribute to the induction of the previously reported autophagic response in TAIII-treated cells. TAIII induced autophagy plays a protective role in TAIII induced death signaling, and failure to mount autophagic response is associated with heightened sensitivity to TAIII induced apoptosis. The multiple death-promoting and apparently tumor-selective responses to TAIII, its ability to inhibit mTORC1, and the possibility of further enhancing its cytotoxicity by pharmacological inhibition of autophagy, make TAIII an attractive candidate for development as a cancer therapeutic agent.

Show MeSH
Related in: MedlinePlus