SCAP (SREBF chaperone) regulates SREBFs (sterol regulatory element binding transcription factors) processing and stability, and, thus, becomes an emerging drug target to treat dyslipidemia and fatty liver disease. However, the current known SCAP inhibitors, such as oxysterols, induce endoplasmic reticulum (ER) stress and NR1H3/LXRα (nuclear receptor subfamily 1 group H member 3)-SREBF1/SREBP-1 c-mediated hepatic steatosis, which severely limited the clinical application of this inhibitor. In this study, we identified a small molecule, lycorine, which binds to SCAP, which suppressed the SREBF pathway without inducing ER stress or activating NR1H3. Mechanistically, lycorine promotes SCAP lysosomal degradation in a macroautophagy/autophagy-independent pathway, a mechanism completely distinct from current SCAP inhibitors. Furthermore, we determined that SQSTM1 captured SCAP after its exit from the ER. The interaction of SCAP and SQSTM1 requires the WD40 domain of SCAP and the TB domain of SQSTM1. Interestingly, lycorine triggers the lysosome translocation of SCAP independent of autophagy. We termed this novel protein degradation pathway as the SQSTM1-mediated autophagy-independent lysosomal degradation (SMAILD) pathway. In vivo, lycorine ameliorates high-fat diet-induced hyperlipidemia, hepatic steatosis, and insulin resistance in mice. Our study demonstrated that the inhibition of SCAP through the SMAILD pathway could be employed as a useful therapeutic strategy for treating metabolic diseases.

Abbreviation

25-OHD: 25-hydroxyvitamin D; 3-MA: 3-methyladenine; ABCG5: ATP binding cassette subfamily G member 5; ABCG8: ATP binding cassette subfamily G member 8; ACACA: acetyl-CoA carboxylase alpha; AEBSF: 4-(2-aminoethyl) benzenesulfonyl fluoride hydrochloride; AHI: anhydroicaritin; AKT/protein kinase B: AKT serine/threonine kinase; APOE: apolipoprotein E; ATF6: activating transcription factor 6; ATG: autophagy-related; BAT: brown adipose tissue; CD274/PD-L1: CD274 molecule; CETSA: cellular thermal shift assay; CMA: chaperone-mediated autophagy; COPII: cytoplasmic coat protein complex-II; CQ: chloroquine; DDIT3/CHOP: DNA damage inducible transcript 3; DNL: de novo lipogenesis; EE: energy expenditure; EGFR: epithelial growth factor receptor; eMI: endosomal microautophagy; ERN1/IRE1α: endoplasmic reticulum to nucleus signaling 1; FADS2: fatty acid desaturase 2; FASN: fatty acid synthase; GOT1/AST: glutamic-oxaloacetic transaminase 1; GPT/ALT: glutamic-pyruvate transaminase; HMGCR: 3-hydroxy-3-methylglutaryl-CoA reductase; HMGCS1: 3-hydroxy-3-methylglutaryl-CoA synthase 1; HSP90B1/GRP94: heat shock protein 90 beta family member 1; HSPA5/GRP78: heat hock protein family A (Hsp70) member 5; HSPA8/HSC70: heat shock protein family A (Hsp70) member 8; INSIG1: insulin induced gene 1; LAMP2A: lysosomal associated membrane protein 2A; LDLR: low density lipoprotein receptor; LyTACs: lysosome targeting chimeras; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MBTPS1: membrane bound transcription factor peptidase, site 1; MEF: mouse embryonic fibroblast; MST: microscale thermophoresis; MTOR: mechanistic target of rapamycin kinase; MVK: mevalonate kinase; PROTAC: proteolysis targeting chimera; RQ: respiratory quotient; SCAP: SREBF chaperone; SCD1: stearoyl-coenzemy A desaturase 1; SMAILD: sequestosome 1 mediated autophagy-independent lysosomal degradation; SQSTM1: sequestosome 1; SREBF: sterol regulatory element binding transcription factor; TNFRSF10B/DR5: TNF receptor superfamily member 10b; TRAF6: TNF receptor associated factor 6; UPR: unfolded protein response; WAT: white adipose tissue; XBP1: X-box binding protein 1

中文翻译：

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发现一种有效的SCAP降解剂，可通过不依赖自噬的溶酶体途径改善HFD诱导的肥胖，高脂血症和胰岛素抵抗

SCAP（SREBF分子伴侣）调节SREBFs（固醇调节元件结合转录因子）的加工和稳定性，因此成为治疗血脂异常和脂肪肝的新兴药物靶标。然而，目前已知的SCAP抑制剂（例如氧固醇）会诱导内质网（ER）应激和NR1H3 /LXRα（核受体亚家族1组H成员3）-SREBF1 / SREBP-1 c介导的肝脂肪变性，这严重限制了临床该抑制剂的应用。在这项研究中，我们确定了一个小分子，lycorine，它与SCAP结合，可以抑制SREBF途径而不会引起ER应激或激活NR1H3。从机理上讲，赖氨酸在大自噬/自噬非依赖性途径中促进SCAP溶酶体降解，这种机制与目前的SCAP抑制剂完全不同。此外，我们确定SQSTM1从ER退出后捕获了SCAP。SCAP和SQSTM1的交互需要SCAP的WD40域和SQSTM1的TB域。有趣的是，肾上腺素触发SCAP的溶酶体易位，而与自噬无关。我们称这种新的蛋白质降解途径为SQSTM1介导的自噬依赖性溶酶体降解（SMAILD）途径。在体内，lycorine可改善高脂饮食诱导的高脂血症，肝脂肪变性和小鼠的胰岛素抵抗。我们的研究表明，通过SMAILD途径抑制SCAP可以用作治疗代谢性疾病的有效治疗策略。

缩写

25-OHD：25-羟基维生素D；3-MA：3-甲基腺嘌呤；ABCG5：ATP结合盒亚家族G成员5；ABCG8：ATP结合盒亚家族G成员8；ACACA：乙酰辅酶A羧化酶α；AEBSF：4-（2-氨基乙基）苯磺酰氟盐酸盐；AHI：脱水甘油；AKT /蛋白激酶B：AKT丝氨酸/苏氨酸激酶；APOE：载脂蛋白E；ATF6：激活转录因子6；ATG：自噬相关；BAT：褐色脂肪组织；CD274 / PD-L1：CD274分子；CETSA：细胞热位移分析；CMA：伴侣介导的自噬；COPII：胞质外壳蛋白复合物-II；CQ：氯喹；DDIT3 / CHOP：DNA损伤诱导转录本3；DNL：从头开始脂肪生成 EE：能源支出；EGFR：上皮生长因子受体；eMI：内体微自噬；ERN1 /IRE1α：内质网至核的信号传导1；FADS2：脂肪酸去饱和酶2；FASN：脂肪酸合酶；GOT1 / AST：谷氨酸-草酰乙酸转氨酶1；GPT / ALT：谷氨酸丙酮酸转氨酶；HMGCR：3-羟基-3-甲基戊二酰辅酶A还原酶；HMGCS1：3-羟基-3-甲基戊二酰辅酶A合酶1；HSP90B1 / GRP94：热激蛋白90β家族成员1；HSPA5 / GRP78：热激蛋白家族A（Hsp70）的成员5；HSPA8 / HSC70：热激蛋白A家族（Hsp70）成员8；INSIG1：胰岛素诱导的基因1；LAMP2A：溶酶体相关膜蛋白2A；LDLR：低密度脂蛋白受体；LyTACs：靶向嵌合体的溶酶体；MAP1LC3B / LC3B：微管相关蛋白1轻链3 beta；MBTPS1：膜结合转录因子肽酶，位点1；MEF：小鼠胚胎成纤维细胞；MST：微尺度热泳；MTOR：雷帕霉素激酶的机制靶标；MVK：甲羟戊酸激酶；PROTAC：针对嵌合体的蛋白水解；RQ：呼吸商；SCAP：SREBF分子伴侣；SCD1：硬脂酰辅酶A去饱和酶1；SMAILD：螯合体1介导的不依赖自噬的溶酶体降解；SQSTM1：螯合体1；SREBF：固醇调节元件结合转录因子；TNFRSF10B / DR5：TNF受体超家族成员10b；TRAF6：TNF受体相关因子6；UPR：展开的蛋白质反应；WAT：白色脂肪组织；XBP1：X-box结合蛋白1 RQ：呼吸商；SCAP：SREBF分子伴侣；SCD1：硬脂酰辅酶A去饱和酶1；SMAILD：螯合体1介导的不依赖自噬的溶酶体降解；SQSTM1：螯合体1；SREBF：固醇调节元件结合转录因子；TNFRSF10B / DR5：TNF受体超家族成员10b；TRAF6：TNF受体相关因子6；UPR：展开的蛋白质反应；WAT：白色脂肪组织；XBP1：X-box结合蛋白1 RQ：呼吸商；SCAP：SREBF分子伴侣；SCD1：硬脂酰辅酶A去饱和酶1；SMAILD：螯合体1介导的不依赖自噬的溶酶体降解；SQSTM1：螯合体1；SREBF：固醇调节元件结合转录因子；TNFRSF10B / DR5：TNF受体超家族成员10b；TRAF6：TNF受体相关因子6；UPR：展开的蛋白质反应；WAT：白色脂肪组织；XBP1：X-box结合蛋白1