Enhancer of rudimentary homologue interacts with scaffold attachment factor B at the nuclear matrix to regulate SR protein phosphorylation

5 years ago

Enhancer of rudimentary homologue interacts with scaffold attachment factor B at the nuclear matrix to regulate SR protein phosphorylation

Eleni Georgatsou, Maria Papathanassiou, Ilias Mylonis, Sotiria Drakouli, Aggeliki Lyberopoulou

Scaffold attachment factor B1 (SAFB1) is an integral component of the nuclear matrix of vertebrate cells. It binds to DNA on scaffold/matrix attachment region elements, as well as to RNA and a multitude of different proteins, affecting basic cellular activities such as transcription, splicing and DNA damage repair. In the present study, we show that enhancer of rudimentary homologue (ERH) is a new molecular partner of SAFB1 and its 70% homologous paralogue, scaffold attachment factor B2 (SAFB2). ERH interacts directly in the nucleus with the C-terminal Arg-Gly-rich region of SAFB1/2 and co-localizes with it in the insoluble nuclear fraction. ERH, a small ubiquitous protein with striking homology among species and a unique structure, has also been implicated in fundamental cellular mechanisms. Our functional analyses suggest that the SAFB/ERH interaction does not affect SAFB1/2 function in transcription (e.g. as oestrogen receptor α co-repressors), although it reverses the inhibition exerted by SAFB1/2 on the splicing kinase SR protein kinase 1 (SRPK1), which also binds on the C-terminus of SAFB1/2. Accordingly, ERH silencing decreases lamin B receptor and SR protein phosphorylation, which are major SRPK1 substrates, further substantiating the role of SAFB1 and SAFB2 in the co-ordination of nuclear function. The R/G rich C-terminal domain of scaffold attachment factor-B (SAFB)1/2 was found to directly interact with enhancer of rudimentary homologue (ERH). When the ERH concentration is high, SAFBs and ERH form a complex. As a result, SAFB does not exert its inhibitory effect on SR protein kinase 1 (SRPK1) and SR-proteins are phosphorylated. Conversely, when ERH is low, SAFBs inhibit SRPK1 function inside the nucleus.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1111/febs.14141