Protein modifications regulate the role of 14-3-3{gamma} adaptor protein in cAMP-induced steroidogenesis in MA-10 Leydig cells [Cell Biology]

August 1st, 2014 by Aghazadeh, Y., Ye, X., Blonder, J., Papadopoulos, V.

The 14-3-3 protein family comprises adaptors and scaffolds that regulate intracellular signaling pathways. The 14-3-3γ isoform is a negative regulator of steroidogenesis that is hormonally induced and transiently functions at the initiation of steroidogenesis by delaying maximal steroidogenesis in MA-10 mouse tumor Leydig cells. Treatment of MA-10 cells with the cAMP analog 8-Br-cAMP, which stimulates steroidogenesis, triggers the interaction of 14-3-3γ with the steroidogenic acute regulatory protein (STAR) in the cytosol, which limits STAR activity to basal levels. Over time, this interaction ceases, allowing for a 2-fold induction in STAR activity and maximal increase in the rate of steroid formation. The 14-3-3γ-STAR pattern of interaction was found to be opposite that of the 14-3-3γ homodimerization pattern. Phosphorylation and acetylation of 14-3-3γ showed similar patterns to homodimerization and STAR binding, respectively. 14-3-3γ S58 phosphorylation and 14-3-3γ K49 acetylation were blocked using trans-activator of HIV transcription factor 1 (TAT) peptides coupled to 14-3-3γ sequences containing S58 or K49. Blocking either one of these modifications further induced 8-Br-cAMP-induced steroidogenesis while reducing lipid storage, suggesting that the stored cholesterol is used for steroid formation. Taken together, these results indicate that S58 phosphorylation and K49 acetylation of 14-3-3γ occur in a coordinated time-dependent manner to regulate 14-3-3γ homodimerization. 14-3-3γ S58 phosphorylation is required for STAR interactions under control conditions, and 14-3-3γ K49 acetylation is important for the cAMP-dependent induction of these interactions.
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