Department of Life Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel.
National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, Beer Sheva, Israel.
Mol Oncol. 2021 Nov;15(11):3037-3061. doi: 10.1002/1878-0261.12959. Epub 2021 May 4.
SMAC/Diablo, a pro-apoptotic protein, yet it is overexpressed in several cancer types. We have described a noncanonical function for SMAC/Diablo as a regulator of lipid synthesis during cancer cell proliferation and development. Here, we explore the molecular mechanism through which SMAC/Diablo regulates phospholipid synthesis. We showed that SMAC/Diablo directly interacts with mitochondrial phosphatidylserine decarboxylase (PSD) and inhibits its catalytic activity during synthesis of phosphatidylethanolamine (PE) from phosphatidylserine (PS). Unlike other phospholipids (PLs), PE is synthesized not only in the endoplasmic reticulum but also in mitochondria. As a result, PSD activity and mitochondrial PE levels were increased in the mitochondria of SMAC/Diablo-deficient cancer cells, with the total amount of cellular PLs and phosphatidylcholine (PC) being lower as compared to SMAC-expressing cancer cells. Moreover, in the absence of SMAC/Diablo, PSD inhibited cancer cell proliferation by catalysing the overproduction of mitochondrial PE and depleting the cellular levels of PC, PE and PS. Additionally, we demonstrated that both SMAC/Diablo and PSD colocalization in the nucleus resulted in increased levels of nuclear PE, that acts as a signalling molecule in regulating several nuclear activities. By using a peptide array composed of 768-peptides derived from 11 SMAC-interacting proteins, we identified six nuclear proteins ARNT, BIRC2, MAML2, NR4A1, BIRC5 and HTRA2 Five of them also interacted with PSD through motifs that are not involved in SMAC binding. Synthetic peptides carrying the PSD-interacting motifs of these proteins could bind purified PSD and inhibit the PSD catalytic activity. When targeted specifically to the mitochondria or the nucleus, these synthetic peptides inhibited cancer cell proliferation. To our knowledge, these are the first reported inhibitors of PSD acting also as inhibitors of cancer cell proliferation. Altogether, we demonstrated that phospholipid metabolism and PE synthesis regulated by the SMAC-PSD interaction are essential for cancer cell proliferation and may be potentially targeted for treating cancer.
SMAC/Diablo 是一种促凋亡蛋白，但它在几种癌症类型中过度表达。我们已经描述了 SMAC/Diablo 的一种非典型功能，即作为癌症细胞增殖和发育过程中脂质合成的调节剂。在这里，我们探索了 SMAC/Diablo 调节磷脂合成的分子机制。我们表明，SMAC/Diablo 直接与线粒体磷脂酰丝氨酸脱羧酶 (PSD) 相互作用，并在从磷脂酰丝氨酸 (PS) 合成磷脂乙醇胺 (PE) 期间抑制其催化活性。与其他磷脂 (PLs) 不同，PE 不仅在内质网中合成，而且在线粒体中合成。因此，SMAC/Diablo 缺陷型癌细胞的线粒体中 PSD 活性和线粒体 PE 水平增加，而与表达 SMAC 的癌细胞相比，细胞总 PL 和磷脂酰胆碱 (PC) 水平降低。此外，在没有 SMAC/Diablo 的情况下，PSD 通过催化线粒体 PE 的过度产生和耗尽细胞内 PC、PE 和 PS 的水平来抑制癌细胞增殖。此外，我们证明 SMAC/Diablo 和 PSD 在核内的共定位导致核内 PE 水平升高，PE 作为一种信号分子，在调节多种核活性中发挥作用。通过使用由来自 11 种 SMAC 相互作用蛋白的 768 个肽组成的肽阵列，我们鉴定了核蛋白 ARNT、BIRC2、MAML2、NR4A1、BIRC5 和 HTRA2 中的六种。其中五个还通过不参与 SMAC 结合的基序与 PSD 相互作用。携带这些蛋白 PSD 相互作用基序的合成肽可与纯化的 PSD 结合并抑制 PSD 催化活性。当靶向专门针对线粒体或细胞核时，这些合成肽抑制癌细胞增殖。据我们所知，这些是首批报道的 PSD 抑制剂，也可作为癌细胞增殖抑制剂。总的来说，我们证明了 SMAC-PSD 相互作用调节的磷脂代谢和 PE 合成对癌细胞增殖至关重要，并且可能成为治疗癌症的潜在靶点。
