The suppression of MAD1 by AKT-mediated phosphorylation activates MAD1 target genes transcription.
MAX dimerization protein 1 (MAD1) is a transcription suppressor that antagonizes MYC-mediated transcription activation, and the inhibition mechanism occurs mainly through the competition of target genes' promoter MYC binding sites by MAD1. The promoter binding proteins switch between MYC and MAD1 affects cell proliferation and differentiation. However, little is known about MAD1's regulation process in cancer cells. Here, we present evidence that AKT inhibits MAD1-mediated transcription repression by physical interaction with and phosphorylation of MAD1. Phosphorylation reduces the binding affinity between MAD1 and its target genes' promoter and thereby abolishes its transcription suppression function. Mutation of the phosphorylation site from serine to alanine rescues the DNA-binding ability in the presence of activated AKT. In addition, AKT inhibits MAD1-mediated target genes (hTERT and ODC) transcription repression and promotes cell cycle and cell growth. However, mutated S145A MAD1 abrogates the inhibition by AKT. Thus, our results suggest that phosphorylation of MAD1 by AKT inhibits MAD1-mediated transcription suppression and subsequently activates the transcription of MAD1 target genes.
Chou
Chao-Kai
CK
Department of Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
Lee
Dung-Fang
DF
Sun
Hui-Lung
HL
Li
Long-Yuan
LY
Lin
Chun-Yi
CY
Huang
Wei-Chien
WC
Hsu
Jung-Mao
JM
Kuo
Hsu-Ping
HP
Yamaguchi
Hirohito
H
Wang
Ying-Nai
YN
Liu
Mo
M
Wu
Hsin-Yi
HY
Liao
Pao-Chi
PC
Yen
Chia-Jui
CJ
Hung
Mien-Chie
MC
D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D005786:Gene Expression Regulation; D016259:Genes, myc; D006801:Humans; D013058:Mass Spectrometry; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic
D018797:Cell Cycle Proteins; C501384:MAD1L1 protein, human; D009687:Nuclear Proteins; D051057:Proto-Oncogene Proteins c-akt