Sp1 regulates Raf/MEK/ERK-induced p21(CIP1) transcription in TP53-mutated cancer cells. Cell Signal 2015 Mar;27(3):479-86
Date
01/18/2015Pubmed ID
25595558Pubmed Central ID
PMC4333010DOI
10.1016/j.cellsig.2015.01.005Scopus ID
2-s2.0-84922621429 (requires institutional sign-in at Scopus site) 28 CitationsAbstract
We previously reported that the upregulation of mortalin, an Hsp70 family chaperone, is important for B-Raf(V600E) tumor cells to bypass p21(CIP1) expression, which is activated as a tumor-suppressive mechanism in response to aberrant MEK/ERK activation (Wu et al., 2013). Interestingly, mortalin depletion induced p21(CIP1) transcription not only in wild-type TP53 but also in TP53-mutated B-Raf(V600E) cancer cells, suggesting the presence of an additional mechanism for p21(CIP1) regulation. In the present study, using luciferase reporter truncation analysis in a TP53-mutated B-Raf(V600E) cancer cell line, SK-MEL28, we identified a proximal p21(CIP1) promoter region responsive to mortalin depletion. Interestingly, when Sp1-like cis-elements in this promoter region were mutagenized, the p21(CIP1) promoter luciferase reporter was no longer responsive to mortalin depletion. Consistent with this, our ChIP analysis revealed that mortalin knockdown could induce Sp1 binding to p21(CIP1) promoter in a MEK/ERK-dependent manner. Moreover, RNA interference of Sp1 substantially attenuated p21(CIP1) expression induced by mortalin depletion in SK-MEL28 cells. Consistent with this observation in SK-MEL28 cells, Sp1 was necessary for the tamoxifen-regulated ∆Raf-1:ER to induce p21(CIP1) transcription in U251 cells, in which TP53 is mutated. However, in contrast, Sp1 was not necessary for ∆Raf-1:ER to induce p21(CIP1) transcription in LNCaP cells, in which TP53 is wild type. These data suggest that Sp1 may address TP53-independent p21(CIP1) transcription in Raf/MEK/ERK-activated cancer cells and that its requirement in Raf/MEK/ERK-induced p21(CIP1) transcription is subject to TP53 status.
Author List
Karkhanis M, Park JIAuthor
Jong-In Park PhD Professor in the Biochemistry department at Medical College of WisconsinMESH terms used to index this publication - Major topics in bold
Cell Line, TumorCyclin-Dependent Kinase Inhibitor p21
Extracellular Signal-Regulated MAP Kinases
HSP70 Heat-Shock Proteins
Humans
MAP Kinase Kinase Kinases
Mutagenesis, Site-Directed
Promoter Regions, Genetic
Protein Binding
Proto-Oncogene Proteins B-raf
RNA Interference
RNA, Small Interfering
Signal Transduction
Sp1 Transcription Factor
Transcriptional Activation
Tumor Suppressor Protein p53
