Sp1 regulates Raf/MEK/ERK-induced p21(CIP1) transcription in TP53-mutated cancer cells.

Abstract

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.

• Authors: Mansi Karkhanis, Jong-In Park
• Journal: Cellular signalling (Cell Signal) Vol. 27 Issue 3 Pg. 479-86 (Mar 2015) ISSN: 1873-3913 [Electronic] England
• PMID: 25595558 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2015 Elsevier Inc. All rights reserved.

Chemical References

• Cyclin-Dependent Kinase Inhibitor p21
• HSP70 Heat-Shock Proteins
• RNA, Small Interfering
• Sp1 Transcription Factor
• TP53 protein, human
• Tumor Suppressor Protein p53
• mortalin
• Proto-Oncogene Proteins B-raf
• Extracellular Signal-Regulated MAP Kinases
• MAP Kinase Kinase Kinases

Topics

• Cell Line, Tumor
• Cyclin-Dependent Kinase Inhibitor p21 (genetics, metabolism)
• Extracellular Signal-Regulated MAP Kinases (metabolism)
• HSP70 Heat-Shock Proteins (antagonists & inhibitors, genetics, metabolism)
• Humans
• MAP Kinase Kinase Kinases (metabolism)
• Mutagenesis, Site-Directed
• Promoter Regions, Genetic
• Protein Binding
• Proto-Oncogene Proteins B-raf (genetics, metabolism)
• RNA Interference
• RNA, Small Interfering (metabolism)
• Signal Transduction
• Sp1 Transcription Factor (antagonists & inhibitors, genetics, metabolism)
• Transcriptional Activation
• Tumor Suppressor Protein p53 (genetics, metabolism)