ELK-1 ubiquitination status and transcriptional activity are modulated independently of F-Box protein FBXO25

Abstract

The mitogen-responsive, ETS-domain transcription factor ELK-1 stimulates the expression of immediate early genes at the onset of the cell cycle and participates in early developmental programming. ELK-1 is subject to multiple levels of posttranslational control, including phosphorylation, SUMOylation, and ubiquitination. Recently, removal of monoubiquitin from the ELK-1 ETS domain by the Ubiquitin Specific Protease USP17 was shown to augment ELK-1 transcriptional activity and promote cell proliferation. Here we have used coimmunoprecipitation experiments, protein turnover and ubiquitination assays, RNA-interference and gene expression analyses to examine the possibility that USP17 acts antagonistically with the F-box protein FBXO25, an E3 ubiquitin ligase previously shown to promote ELK-1 ubiquitination and degradation. Our data confirm that FBXO25 and ELK-1 interact in HEK293T cells and that FBXO25 is active toward Hand1 and HAX1, two of its other candidate substrates. However, our data indicate that FBXO25 neither promotes ubiquitination of ELK-1 nor impacts on its transcriptional activity and suggest that an E3 ubiquitin ligase other than FBXO25 regulates ELK-1 ubiquitination and function.

Ubiquitin-Mediated Control of ETS Transcription Factors: Roles in Cancer and Development

“…FBXO25 was reported to interact with ELK-1 and promote its polyubiquitination and degradation by the 26S proteasome, thereby impairing ELK-1 target gene transcription [ 88 ]. However, although subsequent, independent work confirmed that FBXO25 interacted with ELK-1 in a region including the CD, its proposed impact on ELK-1 ubiquitination or transcriptional activity could not be substantiated [ 89 ].…”

“…The USP17 family of DUBs comprises a number of very similar proteins originating from a cell-cycle regulated multicopy gene that has oncogene character in a range of cancer pathologies, albeit with noted exceptions [ 90 ]. USP17 was found to interact with ELK-1 in a region encompassing the B-domain and CD (aas 93–189) and efficiently deubiquitinate both mono- and polyubiquitinated ELK-1, thereby augmenting its transcriptional activity, driving target gene expression and cell cycle entry [ 86 , 89 ]. Moreover, expression of a hypo-ubiquitinated ELK-1 mutant, but not wild-type ELK-1, partially rescued the proliferation defect caused by USP17 depletion in HEK293T cells, illustrating the contribution of this mechanism towards mitogen signalling [ 86 ].…”

Analysis of Functional Promoter of Camel FGF21 Gene and Identification of Small Compounds Targeting FGF21 Protein

“…Analysis of the transcription factor binding sites indicates that camel FGF21 promoter shared the most transcription factor binding sites with humans and mice ( Figure 3 ) although with significant differences in promoter sequences ( Figure 1 ) and binding site positions in the promoter. The major functional transcription factors such as SP1 [ 29 , 30 ], NF-1 [ 31 ], GATA1 [ 32 ], YY1 [ 33 ] and Elk-1 [ 34 ] nearly appeared in all mammals, suggesting that the signaling pathways involved in FGF21 gene transcription regulation are conservative in mammals. However, more work is still needed to identify differential transcription factors that can help reveal the specific regulatory patterns of camel FGF21.…”