Galiellalactone is a Direct Inhibitor of STAT3 in Prostate Cancer Cells.

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Galiellalactone is a Direct Inhibitor of STAT3 in Prostate Cancer Cells. / Don-Doncow, Nicholas; Escobar Gabriel, Zilma; Johansson, Martin H; Kjellström, Sven; Garcia, Victor; Munoz, Eduardo; Sterner, Olov; Bjartell, Anders; Hellsten, Rebecka.

In: Journal of Biological Chemistry, Vol. 289, No. 23, 2014, p. 15969-15978.

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Don-Doncow, Nicholas ; Escobar Gabriel, Zilma ; Johansson, Martin H ; Kjellström, Sven ; Garcia, Victor ; Munoz, Eduardo ; Sterner, Olov ; Bjartell, Anders ; Hellsten, Rebecka. / Galiellalactone is a Direct Inhibitor of STAT3 in Prostate Cancer Cells. In: Journal of Biological Chemistry. 2014 ; Vol. 289, No. 23. pp. 15969-15978.

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TY - JOUR

T1 - Galiellalactone is a Direct Inhibitor of STAT3 in Prostate Cancer Cells.

AU - Don-Doncow, Nicholas

AU - Escobar Gabriel, Zilma

AU - Johansson, Martin H

AU - Kjellström, Sven

AU - Garcia, Victor

AU - Munoz, Eduardo

AU - Sterner, Olov

AU - Bjartell, Anders

AU - Hellsten, Rebecka

PY - 2014

Y1 - 2014

N2 - The transcription factor STAT3 is constitutively active in several malignancies including castration-resistant prostate cancer and has been identified as a promising therapeutic target. The fungal metabolite galiellalactone, a STAT3 signaling inhibitor, inhibits the growth, both in vitro and in vivo, of prostate cancer cells expressing active STAT3 and induces apoptosis of prostate cancer stem cell-like cells expressing pSTAT3. However, the molecular mechanism of this STAT3 inhibiting effect by galiellalactone has not been clarified. A biotinylated analogue of galiellalactone (GL-biot) was synthesized to be used for identification of galiellalactone target proteins. By adding streptavidin-sepharose beads to GL-biot treated DU145 cell lysates, STAT3 was isolated and identified as a target protein. Confocal microscopy revealed GL-biot in both the cytoplasm and nucleus of DU145 cells treated with GL-biot, appearing to co-localize with STAT3 in the nucleus. Galiellalactone inhibited STAT3 binding to DNA in DU145 cell lysates without affecting phosphorylation status of STAT3. Mass spectrometry analysis of recombinant STAT3 protein pretreated with galiellalactone revealed three modified cysteines (cys-367, cys-468 and cys-542). We here demonstrate with chemical and molecular pharmacological methods that galiellalactone is a cysteine reactive inhibitor that covalently binds to one or more cysteines in STAT3 and that this leads to inhibition of STAT3 binding to DNA and thus blocks STAT3 signaling without affecting phosphorylation. This further validates galiellalactone as a promising direct STAT3 inhibitor for treatment of castration-resistant prostate cancer.

AB - The transcription factor STAT3 is constitutively active in several malignancies including castration-resistant prostate cancer and has been identified as a promising therapeutic target. The fungal metabolite galiellalactone, a STAT3 signaling inhibitor, inhibits the growth, both in vitro and in vivo, of prostate cancer cells expressing active STAT3 and induces apoptosis of prostate cancer stem cell-like cells expressing pSTAT3. However, the molecular mechanism of this STAT3 inhibiting effect by galiellalactone has not been clarified. A biotinylated analogue of galiellalactone (GL-biot) was synthesized to be used for identification of galiellalactone target proteins. By adding streptavidin-sepharose beads to GL-biot treated DU145 cell lysates, STAT3 was isolated and identified as a target protein. Confocal microscopy revealed GL-biot in both the cytoplasm and nucleus of DU145 cells treated with GL-biot, appearing to co-localize with STAT3 in the nucleus. Galiellalactone inhibited STAT3 binding to DNA in DU145 cell lysates without affecting phosphorylation status of STAT3. Mass spectrometry analysis of recombinant STAT3 protein pretreated with galiellalactone revealed three modified cysteines (cys-367, cys-468 and cys-542). We here demonstrate with chemical and molecular pharmacological methods that galiellalactone is a cysteine reactive inhibitor that covalently binds to one or more cysteines in STAT3 and that this leads to inhibition of STAT3 binding to DNA and thus blocks STAT3 signaling without affecting phosphorylation. This further validates galiellalactone as a promising direct STAT3 inhibitor for treatment of castration-resistant prostate cancer.

U2 - 10.1074/jbc.M114.564252

DO - 10.1074/jbc.M114.564252

M3 - Article

VL - 289

SP - 15969

EP - 15978

JO - Journal of Biological Chemistry

T2 - Journal of Biological Chemistry

JF - Journal of Biological Chemistry

SN - 1083-351X

IS - 23

ER -