A single cell level measurement of StAR expression and activity in adrenal cells.

The Steroidogenic acute regulatory protein (StAR) directs mitochondrial cholesterol uptake through a C-terminal cholesterol binding domain (CBD) and a 62 amino acid N-terminal regulatory domain (NTD) that contains an import sequence and conserved sites for inner membrane metalloproteases. Deletion of the NTD prevents mitochondrial import while maintaining steroidogenesis but with compromised cholesterol homeostasis. The rapid StAR-mediated cholesterol transfer in adrenal cells depends on concerted mRNA translation, p37 StAR phosphorylation and controlled NTD cleavage. The NTD controls this process with two cAMP-inducible modulators of, respectively, transcription and translation SIK1 and TIS11b/Znf36l1. High-resolution fluorescence in situ hybridization (HR-FISH) of StAR RNA resolves slow RNA splicing at the gene loci in cAMP-induced Y-1 cells and transfer of individual 3.5 kb mRNA molecules to mitochondria. StAR transcription depends on the CREB coactivator CRTC2 and PKA inhibition of the highly inducible suppressor kinase SIK1 and a basal counterpart SIK2. PKA-inducible TIS11b/Znf36l1 binds specifically to highly conserved elements in exon 7 thereby suppressing formation of mRNA and subsequent translation. Co-expression of SIK1, Znf36l1 with 3.5 kb StAR mRNA may limit responses to pulsatile signaling by ACTH while regulating the transition to more prolonged stress

类固醇生成急性调节蛋白（StAR）通过一个C末端胆固醇结合结构域（CBD）和一个含导入序列以及内膜金属蛋白酶保守位点的62个氨基酸的N末端调节结构域（NTD）引导线粒体摄取胆固醇。NTD的缺失会阻止线粒体导入，同时维持类固醇生成，但胆固醇稳态会受到损害。肾上腺细胞中StAR介导的胆固醇快速转移依赖于协同的mRNA翻译、p37 StAR磷酸化以及受控制的NTD切割。NTD通过分别调节转录和翻译的两种环磷腺苷酸（cAMP）诱导性调节剂SIK1和TIS11b/Znf36l1来控制这一过程。StAR RNA的高分辨率荧光原位杂交（HR - FISH）解决了在环磷腺苷酸诱导的Y - 1细胞中基因位点处缓慢的RNA剪接以及单个3.5 kb mRNA分子向线粒体的转移问题。StAR转录依赖于环磷腺苷酸反应元件结合蛋白（CREB）共激活因子CRTC2以及蛋白激酶A（PKA）对高诱导性抑制激酶SIK1和一种基础对应物SIK2的抑制。PKA诱导性的TIS11b/Znf36l1特异性结合外显子7中高度保守的元件，从而抑制mRNA的形成和后续翻译。SIK1、Znf36l1与3.5 kb StAR mRNA的共表达可能会限制促肾上腺皮质激素（ACTH）对脉冲信号的反应，同时调节向更长期应激的转变。