AP-1 regulates cyclin D1 and c-MYC transcription in an AKT-dependent manner in response to mTOR inhibition: role of AIP4/Itch-mediated JUNB degradation

R Vartanian, J Masri, J Martin, C Cloninger… - Molecular Cancer …, 2011 - AACR
R Vartanian, J Masri, J Martin, C Cloninger, B Holmes, N Artinian, A Funk, T Ruegg, J Gera
Molecular Cancer Research, 2011AACR
One mechanism by which AKT kinase-dependent hypersensitivity to mammalian target of
rapamycin (mTOR) inhibitors is controlled is by the differential expression of cyclin D1 and c-
MYC. Regulation of posttranscriptional processes has been demonstrated to be crucial in
governing expression of these determinants in response to rapamycin. Our previous data
suggested that cyclin D1 and c-MYC expression might additionally be coordinately
regulated in an AKT-dependent manner at the level of transcription. Under conditions of …
Abstract
One mechanism by which AKT kinase-dependent hypersensitivity to mammalian target of rapamycin (mTOR) inhibitors is controlled is by the differential expression of cyclin D1 and c-MYC. Regulation of posttranscriptional processes has been demonstrated to be crucial in governing expression of these determinants in response to rapamycin. Our previous data suggested that cyclin D1 and c-MYC expression might additionally be coordinately regulated in an AKT-dependent manner at the level of transcription. Under conditions of relatively quiescent AKT activity, treatment of cells with rapamycin resulted in upregulation of cyclin D1 and c-MYC nascent transcription, whereas in cells containing active AKT, exposure repressed transcription. Promoter analysis identified AKT-dependent rapamycin responsive elements containing AP-1 transactivation sites. Phosphorylated c-JUN binding to these promoters correlated with activation of transcription whereas JUNB occupancy was associated with promoter repression. Forced overexpression of JunB or a conditionally active JunB-ER allele repressed cyclin D1 and c-MYC promoter activity in quiescent AKT-containing cells following rapamycin exposure. AIP4/Itch-dependent JUNB protein degradation was found to be markedly reduced in active AKT-containing cells compared with cells harboring quiescent AKT. Moreover, silencing AIP4/Itch expression or inhibiting JNK mediated AIP4 activity abrogated the rapamycin-induced effects on cyclin D1 and c-MYC promoter activities. Our findings support a role for the AKT-dependent regulation of AIP4/Itch activity in mediating the differential cyclin D1 and c-MYC transcriptional responses to rapamycin. Mol Cancer Res; 9(1); 115–30 ©2010 AACR.
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