探討內質網壓力誘導蛋白 HERPUD1 在乳癌細胞 代謝壓力反應中的功能

Abstract

實質固態腫瘤因快速增殖導致血管新生不足，造成氧氣與營養供應不穩，加上代謝廢物堆積，使腫瘤細胞長期處於缺氧與營養缺乏的代謝壓力微環境。代謝壓力會造成癌細胞生長停滯，甚至導致腫瘤中心區域出現壞死，為了適應這種不利的環境，癌細胞會啟動多種壓力反應機制，以維持癌細胞的功能穩定與存活，甚至進一步強化侵襲與轉移能力。然而在代謝壓力下，癌細胞如何調節對代謝壓力的適應並生存，其調控機制仍待完整釐清。 本研究透過分析三陰性乳癌(triple negative breast cancer, TNBC)細胞 MDA-MB-231在葡萄糖剝奪下的基因微陣列(microarray)資料發現，受誘導的上調基因高度富集於內質網壓力與未折疊蛋白反應路徑。在眾多差異表現基因中發現，HERPUD1為上調幅度最顯著且對葡萄糖缺乏高度敏感。此外，利用乳癌公開資料庫進行基因富集(Gene Set Enrichment Analysis, GSEA)分析顯示，HERPUD1的表現與未折疊蛋白反應、蛋白質分泌等路徑呈正相關。HERPUD1為一內質網壓力誘導蛋白，參與內質網相關蛋白降解(ERAD)與蛋白品質控制，其表現常受到未折疊蛋白反應(unfolded protein response, UPR)調控，並與細胞對壓力的適應機制密切相關。 經由細胞實驗發現，HERPUD1主要在三陰性乳癌中被誘導，且其蛋白質表現僅在葡萄糖缺乏時明顯上升；機制層面上，我們發現葡萄糖缺乏所誘導的 HERPUD1上調不依賴ROS/p38訊號，且主要透過未折疊蛋白反應中的IRE1⍺分支調控。在功能上，HERPUD1敲低會使三陰性乳癌細胞於葡萄糖缺乏下的未折疊蛋白反應訊號顯著增強與延長，且自噬通量顯著提高，顯示在HERPUD1缺失的情況下，細胞可能透過代償性自噬協助清除異常蛋白以維持蛋白質恆定(proteostasis)來維持細胞存活與增殖。 綜合上述，我們發現HERPUD1是三陰性乳癌細胞應對代謝壓力的關鍵調節蛋白，在葡萄糖缺乏下透過IRE1⍺分支被誘導表現，並藉由調控內質網壓力強度與抑制過度自噬，在細胞壓力適應與生長控制間取得平衡。

Solid tumors often grow in metabolically stressed microenvironments due to their rapid proliferation, which leads to insufficient and abnormal angiogenesis. As a result, tumor cells experience hypoxia, nutrient deprivation, and accumulation of acidic waste products. These conditions inhibit tumor growth and may cause central necrosis. To survive, cancer cells adapt through metabolic reprogramming and activation of stress response pathways, but the mechanisms underlying such as adaptations remain incompletely understood. Through analysis of in-house microarray data from the triple-negative breast cancer (TNBC) cell line MDA-MB-231 under glucose deprivation, HERPUD1 was identified as a highly sensitive candidate gene significantly enriched in endoplasmic reticulum (ER) stress and unfolded protein response (UPR) pathways. This induction was specific to the triple-negative breast cancer (TNBC) subtype and glucose levels, with no comparable protein-level response to glutamine or arginine withdrawal. Mechanistically, glucose deprivation induced HERPUD1 expression was independent of ROS/p38 signaling but was regulated via the IRE1⍺ signaling axis. Knockdown of HERPUD1 in TNBC cells exacerbated UPR signaling under glucose deprivation. And further investigation revealed that the loss of HERPUD1 significantly accelerated autophagic flux, supported by LC3 conversion and LC3 dynamics. This compensatory autophagy may facilitate the clearance of abnormal proteins to maintain proteostasis. Furthermore, absence of HERPUD1 conferred a survival advantage and enhanced colony-formation ability under low-glucose conditions, suggesting that HERPUD1 constrained the survival and clonogenic growth of TNBC cells under glucose deprivation. This benefit was autophagy-dependent as it could be abolished by inhibiting autophagic flux. In conclusion, HERPUD1 is a critical regulator that balances stress adaptation and growth control by modulating ER stress intensity and suppressing excessive autophagy via the IRE1⍺ axis.