A novel evolutionarily conserved element is a general transcriptional repressor of p21WAF¹/CIP¹.
The effective induction of p21(WAF1/CIP1/Cdkn1a) (p21) expression in p53-negative cancer cells is an important avenue in cancer management. We investigated the ability of various common chemotherapeutic drugs to induce p21 expression in p53-negative cancer cells and showed that the induction of p21 expression by oxaliplatin is caused by the derepression of a previously unrecognized negative regulatory element with a Sp1/Sp3 palindrome sequence core at -216 to -236 of the p21 proximal promoter. Electrophoretic mobility shift and antibody super-shift assays confirmed the specific binding of Sp1/Sp3, and showed that the oxaliplatin-mediated derepression of p21 transcription was associated with an increased Sp1/Sp3 phosphorylation and binding affinity to the oxaliplatin-responsive element. A search of the ENCODE database for vertebrate-conserved genomic elements identified the Sp1/Sp3 palindrome element as the only vertebrate-conserved element within the 500-bp proximal p21 promoter region, indicating its fundamental importance. In in vivo competition assays, transfected synthetic Sp1/Sp3 palindrome elements derepressed the cotransfected or endogenous p21 promoter in a dosage-dependent manner. This derepression was not seen in oxaliplatin-treated cells, suggesting that the exogenous Sp1/Sp3 palindrome and oxaliplatin had the same downstream signaling target. Taken together, our results revealed, for the first time, this evolutionarily conserved Sp1/Sp3 palindrome element in the proximal p21 promoter that serves as a regulatory repressor to maintain p21 basal level expression.
School of Pharmacy, Shanghai Jiao Tong University, Shanghai, China.
Weiguo
W
Xu
Qi
Q
Zhu
Zhenghua
Z
Wu
Hao
H
Guo
Fengjuan
F
Wu
Dhahiri S
DS
Mashausi
Chengjie
C
Zheng
Dawei
D
Li
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001665:Binding Sites; D045744:Cell Line, Tumor; D017124:Conserved Sequence; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000096:biosynthesis / Q000235:genetics*; D063185:Epigenetic Repression; D005260:Female; D006801:Humans; D055029:Inverted Repeat Sequences; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009944:Organoplatinum Compounds / Q000494:pharmacology; D010051:Ovarian Neoplasms / Q000188:drug therapy* / Q000235:genetics* / Q000378:metabolism; D000077150:Oxaliplatin; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000187:drug effects; D020218:Response Elements; D014162:Transfection; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
D000970:Antineoplastic Agents; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D009944:Organoplatinum Compounds; D000077150:Oxaliplatin