Identification of SWI·SNF Complex Subunit BAF60a as a Determinant of the Transactivation Potential of Fos/Jun Dimers

Abstract

Fos family proteins form stable heterodimers with Jun family proteins, and each heterodimer shows distinctive transactivating potential for regulating cellular growth, differentiation, and development via AP-1 binding sites. However, the molecular mechanism underlying dimer specificity and the molecules that facilitate transactivation remain undefined. Here, we show that BAF60a, a subunit of the SWI⅐SNF chromatin remodeling complex, is a determinant of the transactivation potential of Fos/Jun dimers. BAF60a binds to a specific subset of Fos/Jun heterodimers using two different interfaces for c-Fos and c-Jun, respectively. Only when the functional SWI⅐SNF complex is present, can c-Fos/c-Jun (high affinity to BAF60a) but not Fra-2/JunD (no affinity to BAF60a) induce the endogenous AP-1-regulated genes such as collagenase and c-met. These results indicate that a specific subset of Fos/Jun dimers recruits SWI⅐SNF complex via BAF60a to initiate transcription.Transcription factor AP-1, which plays pivotal roles in cell growth, differentiation, development, and tumor formation, is composed of Fos family proteins (Fos; c-Fos, Fra-1, Fra-2, and FosB) and Jun family proteins (Jun; c-Jun, JunB, and JunD). The members of both families form dimers through a leucine zipper structure; Jun family members can form low-affinity homodimers and high affinity heterodimers with the Fos family (1, 2). However, members of the Fos family do not form stable homodimers. Although these hetero-and homodimers bind to similar sites on DNA (TGAC/GTCA, AP-1 binding sites) through the basic domains of both proteins, each dimer has a distinct transcriptional regulatory function that can be modulated either positively or negatively (3). For example, transcriptional activity of the c-Fos/c-Jun dimer is much higher than the Fra-2/c-Jun dimer. Although functional interactions between some members of the Fos/Jun family of proteins and adaptor proteins such as CREB-binding protein (CBP) or TATA-binding protein (TBP) have been reported (4, 5), crucial proteins that recognize the dimer specificity and/or facilitate the induction of transcriptional initiation were largely unknown. Therefore, we proposed here to isolate such a crucial protein using a yeast two-hybrid system and have demonstrated that BAF60a (6), a component of the SWI⅐SNF chromatin remodeling complex, can select specific Fos/Jun dimers and function as a determinant of transcriptional activation via AP-1 binding sites. EXPERIMENTAL PROCEDURESPlasmid Construction-The Gal4DBD-c-Jun (25-187) fusion construct (pDBLeu-cJ(25-187)) was generated by inserting the 0.49 kilobase pair EheI fragment of the rat c-jun gene into the MscI restriction endonuclease cleavage site within the open reading frame of Gal4DBD. For the construction of template DNA for in vitro translation, we first generated a starter plasmid from pGEM2-475/Jun-D, the translation initiation site of which has a Kozak consensus sequence with a unique NcoI site that is preceded by a fragment 475 sequence for an efficient translational ...

The Brm gene suppressed at the post-transcriptional level in various human cell lines is inducible by transient HDAC inhibitor treatment, which exhibits antioncogenic potential

“…When CD44 and collagenase cDNA probes were used for the nuclear run-on assay, active transcription was detectable in nuclei isolated from MDA-MB435, whereas no signal was detected in those from SW13(vim-) (Figure 1b). These results are consistent with the observation that SW13(vim-) cells never express both of two genes at the transcriptional level (Ito et al, 2001;YamamichiNishina et al, 2003), confirming that the run-on transcription assay faithfully reflects transcriptional activity in these cells.…”

“…These interacting proteins include products of proto-oncogenes such as c-fos, c-jun (Ito et al, 2001), and c-myc (Cheng et al, 1999), and tumor suppressor proteins such as Rb (Dunaief et al, 1994;Trouche et al, 1997;Strobeck et al, 2000), p53 , and b-catenin (Barker et al, 2001). We previously reported that the heterodimer of c-Fos and c-Jun requires functional SWI/SNF complex for transactivation through AP-1 DNA binding sites (Ito et al, 2001). Therefore, this complex would be involved in multiple processes associated with formation or suppression of tumors.…”

SWItch/sucrose nonfermentable (SWI/SNF) complex subunit BAF60a integrates hepatic circadian clock and energy metabolism

“…BAF60a was initially identified as a determinant of the transactivation potential of Fos/Jun dimers to induce the endogenous AP-1-regulated genes such as collagenase and c-met. 32 Its function was further described as a mediator of the antitumor effects of p53, 33 a regulator of hepatic lipid metabolism, 24 and an androgen receptor cofactor that modulates TMPRSS2 expression. 34 This suggests a pleiotropic role of BAF60a in cellular and organismal biology by integrating endocrine, metabolic, and circadian signals.…”

Distinct roles of Jun : Fos and Jun : ATF dimers in oncogenesis

“…Obviously, the actual response of a promoter to changes in Jun activity will depend on multiple parameters, including the activity of the Jun dimer partner, other transcription factors and coactivators acting on the promoter, and the promoter architecture (Falvo et al, 2000;Wathelet et al, 1998). In this respect it should be noted that the Jun, Fos and ATF family members di er in their ability to directly or indirectly interact with the CBP/p300 family of transcriptional co-activators, the Jab1 co-activator, and Swi/Snf chromatin remodeling factors (Lee et al, 1996;Duyndam et al, 1999;Claret et al, 1996;Kawasaki, 1998;Kawasaki et al, 2000;Ito et al, 2001).…”