Hal4 和 Hal5 磷酸酶調控細胞自噬之角色

自噬是酵母菌到哺乳動物體內保存的主要細胞途徑，通過形成細胞質雙膜囊泡,使細胞質蛋白質聚集物和細胞器退化,稱爲自噬細胞。然後這些囊泡與液泡或溶酶體融合，從而導致細胞組分退化並循環利用。自噬功能障礙與神經退行性疾病、癌症、代謝性疾病等多種人類疾病有關。因此這一途徑需要適當的監管以防止有害影響和保持恆常性。自噬機制可分爲誘導、成核、伸長、自噬體完成和融合五個階段。每個階段都由特定的自噬相關蛋白 (Atg 蛋白)和幾種激酶調節。酵母蛋白激酶 Hal4 和 Hal5 是維持 K+ 轉運體 Trk1 在腦糖漿膜上的血漿膜穩定性所需要的兩種功能冗餘 Ser/Thr 蛋白激酶。之前的高吞吐量篩查發現 Hal5 和 Atg31 之間存在相互作用。從這個實驗中，我的研究發現在發芽酵母中淘汰 HAL4 和 HAL5 基因顯示出嚴重的自噬缺陷。本研究旨在探討 Hal4 和 Hal5 蛋白激酶在自噬調節中的作用。實驗結果顯示，缺血細胞在體積自噬早期表現爲嚴重的自噬缺陷。在氮飢餓條件下，Hal4 和 Hal5 蛋白激酶可能與 Atg1 的適當定位有關。結果，在 Hal4 和 Hal5 突變體的 Atg9 磷酸化可以部分地被抑制。最後實驗結果指出，非活性 Hal4 激酶突變體雖有明顯的生長缺陷，但沒有明顯的自噬調節缺陷證據。

關鍵字

細胞自噬；磷酸酶；自噬相關蛋白；非活性激酶突變體

並列摘要

Autophagy is the major cellular pathway conserved from yeast to mammals for the degradation of cytoplasmic protein aggregates and organelles by the formation of cytosolic double- membrane vesicles, called autophagosomes. Then these vesicles fuse with the vacuole or lysosomes, resulting in the degradation and recycling of cellular components. Dysfunction of autophagy is involved in various human diseases, such as neurodegenerative diseases, cancers, and metabolic diseases. Hence, this pathway requires proper regulation to prevent deleterious effects and preserve homeostasis. The autophagy mechanism can be divided into five stages, induction, nucleation, elongation, autophagosome completion and fusion. Each of these stages is regulated by specific autophagy-related proteins (Atg proteins) and several kinases. The yeast protein kinase Hal4 and Hal5 are two functionally redundant Ser/Thr protein kinases required for the maintenance of plasma membrane stability of the K+ transporter Trk1 at the plasma membrane in Saccharomyces cerevisiae. A previous high-throughput screening had found an interaction between Hal5 and Atg31. In addition, previous studies from our laboratory had found that knockout HAL4 and HAL5 genes in budding yeast showed severe autophagy defects. This study aimed to investigate the roles of Hal4 and Hal5 protein kinases in autophagy regulation. The experimental results showed that cells lacking hal4 and hal5 show severe autophagy defects in the early stages of bulk autophagy. Hal4 and Hal5 protein kinases might associate with the proper localization of Atg1 under nitrogen starvation conditions. As a consequence, Atg9 phosphorylation might be partially suppressed in hal4 and hal5 mutants. In addition, the kinase-dead hal4 mutant shows an obvious growth defect, but no clear evidence of autophagy regulation defect.

並列關鍵字

autophagy ； protein kinase ； autophagy-related proteins ； kinase-dead mutant

參考文獻

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