Department of Cell Biology and Anatomy, University of South Carolina School of Medicine, Columbia, South Carolina, USA.
Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, Texas, USA.
J Endocrinol. 2024 Jul 3;262(2). doi: 10.1530/JOE-23-0385. Print 2024 Aug 1.
Cells actively engaged in de novo steroidogenesis rely on an expansive intracellular network to efficiently transport cholesterol. The final link in the transport chain is STARD1, which transfers cholesterol to the enzyme complex that initiates steroidogenesis. However, the regulation of ovarian STARD1 is not fully characterized, and even less is known about the upstream cytosolic cholesterol transporters STARD4 and STARD6. Here, we identified both STARD4 and STARD6 mRNAs in the human ovary but only detected STARD4 protein since the primary STARD6 transcript turned out to be a splice variant. Corpora lutea contained the highest levels of STARD4 and STARD1 mRNA and STARD1 protein, while STARD4 protein was uniformly distributed across ovarian tissues. Cyclic AMP analog (8Br-cAMP) and phorbol ester (PMA) individually increased STARD1 and STARD4 mRNA along with STARD1 protein and its phosphoform in cultured primary human luteinized granulosa cells (hGCs). STARD6 transcripts and STARD4 protein were unresponsive to these stimuli. Combining lower doses of PMA and 8Br-cAMP blunted the 8Br-cAMP stimulation of STARD1 protein. Increasing cholesterol levels by blocking its conversion to steroid with aminoglutethimide or by adding LDL reduced the STARD4 mRNA response to stimuli. Sterol depletion reduced the STARD1 mRNA and protein response to PMA. These data support a possible role for STARD4, but not STARD6, in supplying cholesterol for steroidogenesis in the ovary. We demonstrate for the first time how cAMP, PMA and sterol pathways separately and in combination differentially regulate STARD4, STARD6 and STARD1 mRNA levels, as well as STARD1 and STARD4 protein in human primary ovarian cells.
细胞积极参与从头合成类固醇依赖于一个扩展的细胞内网络,以有效地运输胆固醇。运输链的最后一个环节是 STARD1,它将胆固醇转移到启动类固醇生成的酶复合物。然而,卵巢 STARD1 的调节尚未完全表征,甚至对上游细胞质胆固醇转运蛋白 STARD4 和 STARD6 知之甚少。在这里,我们在人卵巢中鉴定了 STARD4 和 STARD6 的 mRNA,但只检测到 STARD4 蛋白,因为主要的 STARD6 转录本是一个剪接变体。黄体含有最高水平的 STARD4 和 STARD1 mRNA 和 STARD1 蛋白,而 STARD4 蛋白在卵巢组织中均匀分布。环 AMP 类似物(8Br-cAMP)和佛波酯(PMA)单独增加了培养的原代人黄体化颗粒细胞(hGCs)中的 STARD1 和 STARD4 mRNA 以及 STARD1 蛋白及其磷酸化形式。STARD6 转录本和 STARD4 蛋白对这些刺激没有反应。联合使用较低剂量的 PMA 和 8Br-cAMP 减弱了 8Br-cAMP 对 STARD1 蛋白的刺激。用氨基谷氨酸抑制胆固醇转化为类固醇或添加 LDL 增加胆固醇水平会降低 STARD4 mRNA 对刺激的反应。固醇耗竭降低了 PMA 对 STARD1 mRNA 和蛋白的反应。这些数据支持 STARD4 而不是 STARD6 在为卵巢中的类固醇生成提供胆固醇方面可能发挥作用。我们首次证明了 cAMP、PMA 和固醇途径如何分别和组合地差异调节 STARD4、STARD6 和 STARD1 mRNA 水平,以及人原代卵巢细胞中的 STARD1 和 STARD4 蛋白。
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