The Nuclear Factor SPBP Contains Different Functional Domains and Stimulates the Activity of Various Transcriptional Activators

Cecilie Rekdal,Eva Sjøttem,Terje Johansen

doi:10.1074/jbc.m006978200

Cecilie Rekdal, Eva Sjøttem + Show 1 more

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https://doi.org/10.1074/jbc.m006978200

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Abstract

SPBP (stromelysin-1 platelet-derived growth factor-responsive element binding protein) was originally cloned from a cDNA expression library by virtue of its ability to bind to a platelet-derived growth factor-responsive element in the human stromelysin-1 promoter. A 937-amino acid-long protein was deduced from a 3995-nucleotide murine cDNA sequence. By analyses of both human and murine cDNAs, we now show that SPBP is twice as large as originally found. The human SPBP gene contains six exons and is located on chromosome 22q13.1-13.3. Two isoforms differing in their C termini are expressed due to alternative splicing. PCR analyses of multitissue cDNA panels showed that SPBP is expressed in most tissues except for ovary and prostate. Functional mapping revealed that SPBP is a nuclear, multidomain protein containing an N-terminal region with transactivating ability, a novel type of DNA-binding domain containing an AT hook motif, and a bipartite nuclear localization signal as well as a C-terminal zinc finger domain. This type of zinc finger domain is also found in the trithorax family of chromatin-based transcriptional regulator proteins. Using cotransfection experiments, we find that SPBP enhances the transcriptional activity of various transcription factors such as c-Jun, Ets1, Sp1, and Pax6. Hence, SPBP seems to act as a transcriptional coactivator.

Highlights

IntroductionSPBP (stromelysin-1 PDGF1-responsive element-binding protein) was originally isolated from a murine ␭gt cDNA library as a protein that bound to the stromelysin-1 PDGFresponsive element (SPRE) of the human stromelysin-1 promoter [1]
SPBP was originally isolated from a murine ␭gt11 cDNA library as a protein that bound to the stromelysin-1 PDGFresponsive element (SPRE) of the human stromelysin-1 promoter [1]
PCR analyses of multitissue cDNA panels showed that SPBP is expressed in most tissues except for ovary and prostate

Summary

Introduction

SPBP (stromelysin-1 PDGF1-responsive element-binding protein) was originally isolated from a murine ␭gt cDNA library as a protein that bound to the stromelysin-1 PDGFresponsive element (SPRE) of the human stromelysin-1 promoter [1]. Stromelysin-1, known as MMP3, is an extracellular matrix-degrading metalloproteinase that is active against a broad range of substrates These proteases are invariably up-regulated in epithelial cancers, recognized as targets of oncogenic signal transduction pathways and shown to contribute to tumor invasion and metastasis [3, 4]. The stromelysin-1 promoter contains three elements that are important for induction by mitogenic stimuli These are an AP-1 element binding the c-Fos/c-Jun transcription factors, two head-to-head PEA3 elements binding Ets family transcription factors, and the SPRE element that binds SPBP (see Ref. 7 and references therein). Functional mapping revealed SPBP to be a nuclear multidomain protein It contains three nuclear localization signals, a novel type of DNA-binding domain with a single AT-hook, a transactivation domain in the N-terminal end, and in the very C-terminal end an evolutionary conserved zinc finger domain found in the trithorax family of chromatin-based transcriptional regulator proteins. SPBP has the ability to enhance the transcriptional activity of various transcription factors, such as c-Jun, Ets, Sp1, and

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