Protein Kinase A-Dependent Cooperation between GATA and CCAAT/Enhancer-Binding Protein Transcription Factors Regulates Steroidogenic Acute Regulatory Protein Promoter Activity

Abstract

Steroidogenic acute regulatory protein (StAR) is an essential cholesterol transporter in steroidogenic tissues. Hormone-induced StAR expression is regulated through the cAMP-dependent pathway involving activation of protein kinase A (PKA). The StAR promoter contains several conserved DNA regulatory elements. These include binding sites for steroidogenic factor 1, CCAAT/enhancer-binding protein (C/EBP), and GATA transcription factors. Although these elements are important for StAR promoter activity, how the various transcription factors that bind these elements cooperate to confer cAMP responsiveness remains poorly understood. As induction of StAR transcription by cAMP in steroidogenic MA-10 cells does not require de novo protein synthesis, this suggests that all essential transcription factors are present and that posttranslational modifications of the factors are involved. We now report that GATA-4 is phosphorylated in MA-10 cells in response to cAMP and in heterologous CV-1 cells, GATA-4 transcriptional activity is stimulated by PKA. Moreover, we show that GATA-4 and C/EBPbeta directly interact in vitro and in vivo and synergistically activate the StAR promoter in CV-1 cells exclusively in the presence of PKA. As PKA-dependent synergy was also observed with other GATA and C/EBP family members, this transcriptional cooperation may contribute to hormone-stimulated StAR expression in all steroidogenic tissues.

The nuclear receptors NUR77 and SF1 play additive roles with c-JUN through distinct elements on the mouse Star promoter

“…Consistent with this, there have been numerous reports of direct protein-protein interactions involving these transcription factors on the Star promoter in Leydig cells (Reinhart et al 1999, Sugawara et al 2000, Tremblay et al 2002, Manna et al 2003b. In the present study, we have found that NUR77 and c-JUN have additive effects on the mouse Star promoter in Leydig cells.…”

“…All proteins were obtained using the Quick Coupled TnT in vitro transcription/translation kit (Promega Corp, Madison, WI, USA). Proteins were incubated in 500 ml binding buffer (Tremblay et al 2002) with 4 mg NUR77, c-FOS, or c-JUN antisera for 24 h at 4 8C with agitation, followed by an additional 24 h in the presence of 20 ml protein G-Sepharose beads (GE Healthcare, Baie d'Urfe, QC, Canada). Bound immunocomplexes were washed five times in binding buffer, resuspended in 20 ml 2!…”

“…The tissue-and cell-specific expression as well as hormonal regulation of the Star gene in steroidogenic cells is believed to be the result of cooperations between transcription factors. Indeed, various studies of the Star promoter have reported protein-protein interactions between GATA4 and C/EBPb (Tremblay et al 2002), CREB, and SF1 (Manna et al 2003b), SF1 and C/EBPb (Reinhart et al 1999), SP1 and SF1 (Sugawara et al 2000), DLX5/6 and GATA4 (Nishida et al 2008), and between c-JUN and SF1, GATA4, and C/EBPb (Manna et al 2004).…”

Transcriptomic characterization of fibrolamellar hepatocellular carcinoma

“…The promoter activity of GATA-6, in turn, is activated by PKA by phosphorylation on a unique serine (25).…”

“…In normal tissue, PKA is involved in many cellular functions (23). It phosphorylates many targets, including transcription factors such as cAMP response element-binding protein (CREB) (24), GATA3, GATA6 (25), NF-κB (26), β-catenin [activating downstream elements of the wnt pathway (27)], the transcription coactivator yes-associated protein 1 (YAP) (28), and ETV1 (29) and indirectly activates XBP1 (30). Any or all of these molecular events could have significant effects on gene expression.…”