Hierarchical Requirement of SWI/SNF in Retinoblastoma Tumor Suppressor-mediated Repression of Plk1

Abstract

Plk1 (Polo-like kinase 1) is a critical regulator of cell cycle progression that harbors oncogenic activity and exhibits aberrant expression in multiple tumors. However, the mechanism through which Plk1 expression is regulated has not been extensively studied. Here we demonstrate that Plk1 is a target of the retinoblastoma tumor suppressor (RB) pathway. Activation of RB and related pocket proteins p107/p130 mediate attenuation of Plk1. Conversely, RB loss deregulates the control of Plk1 expression. RB pathway activation resulted in the repression of Plk1 promoter activity, and this action was dependent on the SWI/SNF chromatin remodeling complex. Although SWI/SNF subunits are lost during tumorigenesis and cooperate with RB for transcriptional repression, the mechanism through which SWI/ SNF impinges on RB action is unresolved. Therefore, we delineated the requirement of SWI/SNF for three critical facets of Plk1 promoter regulation: transcription factor binding, corepressor binding, and histone modification. We find that E2F4 and pocket protein association with the Plk1 promoter is independent of SWI/SNF. However, these analyses revealed that SWI/SNF is required for histone deacetylation of the Plk1 promoter. The importance of SWI/SNF-dependent histone deacetylation of the Plk1 promoter was evident, because blockade of this event restored Plk1 expression in the presence of active RB. In summary, these data demonstrate that Plk1 is a target of the RB pathway. Moreover, these findings demonstrate a hierarchical role for SWI/SNF in the control of promoter activity through histone modification.

Coordinate regulation of Fanconi anemia gene expression occurs through the Rb/E2F pathway

“…To activate the endogenous Rb pathway, adenoviral transduction of TSUPr-1 cells with p16INK4a was utilized (Gunawardena et al, 2004). Western blot analysis confirmed substantial downregulation of FANCD2 by p16 INK4a at the level of protein expression (Figure 4b), and the co-repression of FANCA and G at the level of mRNA was verified in this cell system (Figure 2d).…”

Dynamic chromatin: concerted nucleosome remodelling and acetylation

“…For example, the human SWI/SNF complex contributes to repression of cell cycle genes, including the Plk1 gene, through interaction with the promoter-bound retinoblastoma-E2F complex. Interestingly, the hypoacetylation characteristic of the inactive Plk1 promoter and concomitant repression was no longer observable in the absence of SWI/SNF although the retinoblastoma-E2F repression complex was still bound to the promoter (Gunawardena et al, 2004). This may suggest a role of the SWI/SNF complex in facilitating the action of a histone deacetylase, however it remains to be explored whether this effect is direct.…”

Polo-Like Kinase 1: Target and Regulator of Transcriptional Control

“…15,30 Nevertheless, deletion of the E2F site had no significant effect on Plk1 promoter activity in response to p21. 27 However, the E2F binding site contributes to the negative regulation of the Plk1 promoter by the retinoblastoma tumor suppressor (RB) pathway, 31 which is independent of the CDE/CHR element. Plk1 is transcriptionally repressed by activated RB and related pocket proteins p107/p130.…”