HDAC inhibitors suppress c-Jun/Fra-1-mediated proliferation through transcriptionally downregulating MKK7 and Raf1 in neuroblastoma cells

Abstract

Activator protein 1 (AP-1) is a transcriptional factor composed of the dimeric members of bZIP proteins, which are frequently deregulated in human cancer cells. In this study, we aimed to identify an oncogenic AP-1 dimer critical for the proliferation of neuroblastoma cells and to investigate whether histone deacetylase inhibitors (HDACIs), a new generation of anticancer agents, could target the AP-1 dimer. We report here that HDACIs including trichostatin A, suberoylanilidehydroxamic acid, valproic acid and M344 can transcriptionally suppress both c-Jun and Fra-1, preceding their inhibition of cell growth. c-Jun preferentially interacting with Fra-1 as a heterodimer is responsible for AP-1 activity and critical for cell growth. Mechanistically, HDACIs suppress Fra-1 expression through transcriptionally downregulating Raf1 and subsequently decreasing MEK1/2-ERK1/2 activity. Unexpectedly, HDACI treatment caused MKK7 downregulation at both the protein and mRNA levels. Deletion analysis of the 5′-flanking sequence of the MKK7 gene revealed that a major element responsible for the downregulation by HDACI is located at −149 to −3 relative to the transcriptional start site. Knockdown of MKK7 but not MKK4 remarkably decreased JNK/c-Jun activity and proliferation, whereas ectopic MKK7-JNK1 reversed HDACI-induced c-Jun suppression. Furthermore, suppression of both MKK-7/c-Jun and Raf-1/Fra-1 activities was involved in the tumor growth inhibitory effects induced by SAHA in SH-SY5Y xenograft mice. Collectively, these findings demonstrated that c-Jun/Fra-1 dimer is critical for neuroblastoma cell growth and that HDACIs act as effective suppressors of the two oncogenes through transcriptionally downregulating MKK7 and Raf1.

MKK7 transcription positively or negatively regulated by SP1 and KLF5 depends on HDAC4 activity in glioma

“…Total RNA was extracted, and reverse transcription was performed to obtain cDNA as described previously . The expression levels of MKK7 , UPAR , MMP14(MT1‐MMP) , CYCLIN D1 and the housekeeping gene GAPDH or ACTIN were amplified by the gene‐specific primers listed in Supporting Information.…”

“…Transfection and luciferase assays were performed as described previously . The small interfering RNAs (siRNAs) targeting MKK7, MKK4, HDAC4, SP1 and KLF5 are listed in Supporting Information.…”

“…Human U87MG xenografts were established as described previously . All experimental protocols for tumor xenografts were approved by the Animal Care and Use Committee of Guangzhou Medical University.…”

“…To determine anchorage‐independent growth, cells were grown in soft agar as described previously . Briefly, cells were resuspended in medium supplemented with agar at a final concentration of 0.325%.…”

HTP Nutraceutical Screening for Histone Deacetylase Inhibitors and Effects of HDACis on Tumor-suppressing miRNAs by Trichostatin A and Grapeseed (Vitis vinifera) in HeLa cells

“…With the overwhelming surge of HDACis being sought worldwide for nearly every type of cancer (e.g. ovarian (15) neuroblastoma (16) pancreatic (17) liver (18) colon (19) and cervical cancer (20)), a database (HDACiDB) has been established to accommodate this wealth of information. (21) Several mechanisms have been discovered as to how HDACis carry out their anti-tumor effects, including a re-expression of tumor suppressors (e.g.…”