Complex mutual regulation of facilitates chromatin transcription (FACT) subunits on both mRNA and protein levels in human cells

Abstract

rePortFacilitates chromatin transcription (FaCt) is a chromatin remodeling complex with two subunits: SSrP1 and SPt16. Mechanisms controlling FaCt levels are of interest, since the complex is not expressed in most differentiated cells, but is frequently upregulated in cancer, particularly in poorly differentiated, aggressive tumors. Moreover, inhibition of FaCt expression or function in tumor cells interferes with their survival. Here we demonstrate that SSrP1 and SPt16 protein levels decline upon induction of cellular differentiation or senescence in vitro and that similar declines in protein levels for both SSrP1 and SPt16 occur upon rNai-mediated knockdown of either SSrP1 or SPt16. the interdependence of SSrP1 and SPt16 protein levels was found to be due to their association with SSrP1 and SPt16 mrNas, which stabilizes the proteins. In particular, presence of SSrP1 mrNa is critical for SPt16 protein stability. In addition, binding of SSrP1 and SPt16 mrNas to the FaCt complex increases the stability and efficiency of translation of the mrNas. these data support a model in which the FaCt complex is stable when SSrP1 mrNa is present, but quickly degrades when SSrP1 mrNa levels drop. In the absence of FaCt complex, SSrP1 and SPt16 mrNas are unstable and inefficiently translated, making reactivation of FaCt function unlikely in normal cells. thus, we have described a complex and unusual mode of regulation controlling cellular FaCt levels that results in amplified and stringent control of FaCt activity. the FaCt dependence of tumor cells suggests that mechanisms controlling FaCt levels could be targeted for anticancer therapy.

Facilitates Chromatin Transcription Complex Is an “Accelerator” of Tumor Transformation and Potential Marker and Target of Aggressive Cancers

“…2F). Since a parallel study demonstrated co-regulation of SSRP1 and SPT16 levels, shRNA against either FACT subunit effectively eliminated both SSRP1 and SPT16 (Safina et al, 2013). We found that FACT KD suppressed growth of all tumor cells, but had a smaller or no effect on growth of non-transformed cells (Fig.…”

“…1B and C). This is most likely due to the demonstrated dependence of SPT16 protein levels on SSRP1 (Safina et al, 2013). Nevertheless, as for SSRP1 mRNA, a significant number of tumors with very high levels of SPT16 mRNA were observed among various types of cancer.…”

“…This likely derives from the unusual mechanism of SSRP1 and SPT16 co-regulation that we recently described in which the stability of both proteins depends upon formation of the FACT complex and stability of the complex is determined by presence of the SSRP1 mRNA (Safina et al, 2013). In this way, an increase of SSRP1 mRNA is sufficient to drive elevation of both SSRP1 and SPT16 proteins.…”

The FACT Complex Promotes Avian Leukosis Virus DNA Integration

“…In the absence of SSRP1 mRNA, both protein components are depleted. Similarly, when SSRP1 mRNA is overexpressed, Spt16 protein levels also increase (38).…”

“…To determine the effect of the FACT complex on ALV integration in infected cells, we employed a chicken cell line (DT40) with various levels of expression of the FACT complex. Previous research has shown that the expression and abundance of the FACT complex are regulated by a complex feedback loop in which SSRP1 mRNA plays a critical role (38). The presence of SSRP1 mRNA is essential for the stability of the Spt16 protein and the FACT complex as a whole.…”