A chemical biology screen identifies glucocorticoids that regulate c-maf expression by increasing its proteasomal degradation through up-regulation of ubiquitin.
The oncogene c-maf is frequently overexpressed in multiple myeloma cell lines and patient samples and contributes to increased cellular proliferation in part by inducing cyclin D2 expression. To identify regulators of c-maf, we developed a chemical screen in NIH3T3 cells stably overexpressing c-maf and the cyclin D2 promoter driving luciferase. From a screen of 2400 off-patent drugs and chemicals, we identified glucocorticoids as c-maf-dependent inhibitors of cyclin D2 transactivation. In multiple myeloma cell lines, glucocorticoids reduced levels of c-maf protein without influencing corresponding mRNA levels. Subsequent studies demonstrated that glucocorticoids increased ubiquitination-dependent degradation of c-maf and up-regulated ubiquitin C mRNA. Moreover, ectopic expression of ubiquitin C recapitulated the effects of glucocorticoids, demonstrating regulation of c-maf protein through the abundance of the ubiquitin substrate. Thus, using a chemical biology approach, we identified a novel mechanism of action of glucocorticoids and a novel mechanism by which levels of c-maf protein are regulated by the abundance of the ubiquitin substrate.
Mao
Xinliang
X
Princess Margaret Hospital, Ontario Cancer Institute, Toronto, ON, Canada.
Stewart
A Keith
AK
Hurren
Rose
R
Datti
Alessandro
A
Zhu
Xuegong
X
Zhu
Yuanxiao
Y
Shi
Changxin
C
Lee
Kyle
K
Tiedemann
Rodger
R
Eberhard
Yanina
Y
Trudel
Suzanne
S
Liang
Shengben
S
Corey
Seth J
SJ
Gillis
Lisa C
LC
Barber
Dwayne L
DL
Wrana
Jeffery L
JL
Ezzat
Shereen
S
Schimmer
Aaron D
AD
D000818:Animals; D056742:Cyclin D2; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D004353:Drug Evaluation, Preclinical; D005938:Glucocorticoids / Q000737:chemistry / Q000494:pharmacology*; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D051379:Mice; D041681:NIH 3T3 Cells; D011401:Promoter Regions, Genetic / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D051257:Proto-Oncogene Proteins c-maf / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects; D025801:Ubiquitin / Q000378:metabolism*; D054875:Ubiquitination / Q000187:drug effects*; D015854:Up-Regulation / Q000187:drug effects*
C486196:Ccnd2 protein, mouse; D056742:Cyclin D2; D016213:Cyclins; D005938:Glucocorticoids; C495608:Maf protein, mouse; D051257:Proto-Oncogene Proteins c-maf; D025801:Ubiquitin; D008156:Luciferases; D046988:Proteasome Endopeptidase Complex