Nucleolin regulates c-Jun/Sp1-dependent transcriptional activation of cPLA2  in phorbol ester-treated non-small cell lung cancer A549 cells

Abstract

The expression of cPLA2 is critical for transformed growth of non-small cell lung cancer (NSCLC). It is known that phorbol 12-myristate 13-acetate (PMA)-activated signal transduction pathway is thought to be involved in the oncogene action in NSCLC and enzymatic activation of cPLA2. However, the transcriptional regulation of cPLA2α in PMA-activated NSCLC is not clear. In this study, we found that PMA induced the mRNA level and protein expression of cPLA2α. In addition, two Sp1-binding sites of cPLA2α promoter were required for response to PMA and c-Jun overexpression. Small interfering RNA (siRNA) of c-Jun and nucleolin inhibited PMA induced the promoter activity and protein expression of cPLA2α. Furthermore, PMA stimulated the formation of c-Jun/Sp1 and c-Jun/nucleolin complexes as well as the binding of these transcription factor complexes to the cPLA2α promoter. Although Sp1-binding sites were required for the bindings of Sp1 and nucleolin to the promoter, the binding of nucleolin or Sp1 to the promoter was independent of each other. Our results revealed that c-Jun/nucleolin and c-Jun/Sp1 complexes play an important role in PMA-regulated cPLA2α gene expression. It is likely that nucleolin binding at place of Sp1 on gene promoter could also mediate the regulation of c-Jun/Sp1-activated genes.

Functional analysis of the ‐2548G/A leptin gene polymorphism in breast cancer cells

“…17 Here we investigated if human breast cancer cells contain the Lep-2548G/A polymorphism and if the presence of this variant can affect leptin gene expression. Because the Lep-2548G/A site in the leptin promoter is proximal to Sp1 binding motif 23 and nucleolin could interact with Sp1 25 and bind his consensus sites, 24 we focused on the interplay between Lep-2548G/A and the two transcriptional regulators in the process of basal and insulininduced leptin mRNA synthesis.…”

“…22 The Lep-2548 does not map to any known regulatory site, but is proximal to an Sp1 binding motif (CCCGCCT; -2539/-2534) that is known to be regulated by insulin in breast cancer cells. 23 Nucleolin is another nuclear factor that can bind a Sp1 consensus site in the promoter of cytosolic phospholipase A 2 (cPLA 2 ) 24 and that can interact with Sp1, as reported for human keratinocyte (HaCat) cell extracts. 25 Nucleolin is a multifunctional phosphoprotein involved in ribosomal RNA transcription, maturation and assembly, 26 chromatin decondensation 27 as well as transcriptional regulation, 28 including modulation of Sp1-dependent gene expression.…”

“…23 Interestingly, a Sp1-binding sequences of the cytosolic phospholipase A 2 promoter seem to be also recognized by another transcriptional regulator, nucleolin. 24 It has also been proved a protein-protein interaction between Sp1 and nucleolin in human keratinocyte (HaCat) cell extracts. 25 Here we investigated how the presence of the Lep-2548G/A polymorphism might affect insulindependent leptin transcription.…”

“…25 Nucleolin is a multifunctional phosphoprotein involved in ribosomal RNA transcription, maturation and assembly, 26 chromatin decondensation 27 as well as transcriptional regulation, 28 including modulation of Sp1-dependent gene expression. 24 Furthermore, insulin may induce changes in the phosphorilation of nucleolin. 29 Consequently, we studied in breast cancer cell models if the occurrence of the Lep-2548G/A polymorphism can enhance basal and insulin-induced leptin expression via Sp1-and nucleolin-dependent mechanisms.…”

RNA-binding protein nucleolin in disease

“…107 Activation of PKC leading to nucleolin phosphorylation was proposed to mediate the transcriptional activation of the cytosolic phospholipase A 2 (cPLA 2 ) by transcription factors c-Jun and Sp1 and to affect NFκB transcriptional activity. [107][108][109] Other post-translational modifications of nucleolin. Nucleolin is also post-translationally modified via methylation, glycosylation and ADP-ribosylation.…”