TY - JOUR
T1 - PPARγ ligands inhibit telomerase activity and hTERT expression through modulation of the Myc/Mad/Max network in colon cancer cells
AU - Toaldo, Cristina
AU - Pizzimenti, Stefania
AU - Cerbone, Angelo
AU - Pettazzoni, Piergiorgio
AU - Menegatti, Elisa
AU - Daniela, Berardi
AU - Minelli, Rosalba
AU - Giglioni, Barbara
AU - Dianzani, Mario Umberto
AU - Ferretti, Carlo
AU - Barrera, Giuseppina
PY - 2010/6
Y1 - 2010/6
N2 - In human cells the length of telomeres depends on telomerase activity. This activity and the expression of the catalytic subunit of human telomerase reverse transcriptase (hTERT) is strongly up-regulated in most human cancers. hTERT expression is regulated by different transcription factors, such as c-Myc, Mad1 and Sp1. In this study, we demonstrated that 15d-PG J2 and rosiglitazone (an endogenous and synthetic peroxisome proliferators activated receptor γ (PPARγ) ligand, respectively) inhibited hTERT expression and telomerase activity in CaCo-2 colon cancer cells. Moreover, both ligands inhibited c-Myc protein expression and its E-box DNA binding activity. Additionally, Mad1 protein expression and its E-box DNA binding activity were strongly increased by 15d-PG J2 and, to a lesser extent, by rosiglitazone. Sp1 transcription factor expression and its GC-box DNA binding activity were not affected by both PPARγ ligands. Results obtained by transient transfection of CaCo-2 cells with pmaxFP-Green-PRL plasmid constructs containing the functional hTERT core promoter (including one E-box and five GC-boxes) and its E-box deleted sequences, cloned upstream of the green fluorescent protein reporter gene, demonstrated that 15d-PG J2, and with minor effectiveness, rosiglitazone, strongly reduced hTERT core promoter activity. E-boxes for Myc/Mad/Max binding showed a higher activity than GC-boxes for Sp1. By using GW9662, an antagonist of PPARγ, we demonstrated that the effects of 15d-PG J2 are completely PPARγ independent, whereas the effects of rosiglitazone on hTERT expression seem to be partially PPARγ independent. The regulation of hTERT expression by 15d-PG J2 and rosiglitazone, through the modulation of the Myc/Max/Mad1 network, may represent a new mechanism of action of these substances in inhibiting cell proliferation.
AB - In human cells the length of telomeres depends on telomerase activity. This activity and the expression of the catalytic subunit of human telomerase reverse transcriptase (hTERT) is strongly up-regulated in most human cancers. hTERT expression is regulated by different transcription factors, such as c-Myc, Mad1 and Sp1. In this study, we demonstrated that 15d-PG J2 and rosiglitazone (an endogenous and synthetic peroxisome proliferators activated receptor γ (PPARγ) ligand, respectively) inhibited hTERT expression and telomerase activity in CaCo-2 colon cancer cells. Moreover, both ligands inhibited c-Myc protein expression and its E-box DNA binding activity. Additionally, Mad1 protein expression and its E-box DNA binding activity were strongly increased by 15d-PG J2 and, to a lesser extent, by rosiglitazone. Sp1 transcription factor expression and its GC-box DNA binding activity were not affected by both PPARγ ligands. Results obtained by transient transfection of CaCo-2 cells with pmaxFP-Green-PRL plasmid constructs containing the functional hTERT core promoter (including one E-box and five GC-boxes) and its E-box deleted sequences, cloned upstream of the green fluorescent protein reporter gene, demonstrated that 15d-PG J2, and with minor effectiveness, rosiglitazone, strongly reduced hTERT core promoter activity. E-boxes for Myc/Mad/Max binding showed a higher activity than GC-boxes for Sp1. By using GW9662, an antagonist of PPARγ, we demonstrated that the effects of 15d-PG J2 are completely PPARγ independent, whereas the effects of rosiglitazone on hTERT expression seem to be partially PPARγ independent. The regulation of hTERT expression by 15d-PG J2 and rosiglitazone, through the modulation of the Myc/Max/Mad1 network, may represent a new mechanism of action of these substances in inhibiting cell proliferation.
KW - 15-deoxy-prostaglandin J2
KW - CaCo-2 cells
KW - GW9662
KW - H-TERT
KW - Myc/Mad/Max network
KW - PPARγ ligands
KW - Rosiglitazone
KW - Sp1
KW - Telomerase activity
UR - http://www.scopus.com/inward/record.url?scp=77955132089&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=77955132089&partnerID=8YFLogxK
U2 - 10.1111/j.1582-4934.2009.00966.x
DO - 10.1111/j.1582-4934.2009.00966.x
M3 - Article
C2 - 19912441
AN - SCOPUS:77955132089
SN - 1582-1838
VL - 14
SP - 1347
EP - 1357
JO - Journal of Cellular and Molecular Medicine
JF - Journal of Cellular and Molecular Medicine
IS - 6 A
ER -