Cdk4-Cyclin D1對於細胞生長之角色探討

細胞增生(proliferation)需要由細胞生長(cell growth)的推動，細胞生長進行一連串的巨分子合成增加細胞質量。為了能夠進行細胞生長，細胞代謝狀況需要進行代謝重整(metabolic reprogramming)，以利細胞質量(biomass)的累積。Growth factor signaling以及營養訊息匯入PI3K/AKT/mTOR pathway，透過對4E-BP的調控使得c-Myc大量表現，c-Myc與PI3K/AKT/mTOR pathway共同作用促使粒線體(mitochondria)代謝重整以及Warburg effect，造成細胞生長時特殊的代謝狀況，c-Myc也透過下游分子的作用促使粒線體的生成，幫助細胞生長。Hif-1α透過許多層次上的調控抑制c-Myc的活性，影響代謝重整以及粒線體生成，干擾細胞生長，但是Hif-1α同在mTOR/4E-BP pathway調控之下大量表現，Hif-1α必需透過PHD系統不斷分解，PHD系統的活性反應粒線體狀況，正常的粒線體狀況維持PHD系統活性造成Hif-1α大量分解，維持細胞生長的進行。Cdk4/cyclinD1 complex也是促進細胞生長重要的分子，其cyclinD1的表現也在mTOR/4E-BP pathway調控之下，過去Cdk4/cyclinD1 complex的研究集中在G1-S transition的角色，透過對於Rb的作用，促進細胞週期(cell cycle)的進展。但是有些實驗的結果顯示Cdk4/cyclinD1 complex的oncogene功能不是透過對Rb的抑制作用，而是對於細胞生長上有促進的功能。在果蠅系統中Cdk4/cyclinD complex透過Hph(果蠅PHD)執行其細胞生長功能，顯示Cdk4/cyclinD1 complex的活性也影響PHD系統，透露Cdk4/cyclinD1 complex的活性可能參與在c-Myc與Hif-1α之間的分子網絡。在人類纖維母細胞WI38中，處理Cdk4/cyclin D1 complex活性抑制劑Fascaplysin，抑制Cdk4/cyclin D1 complex的kinase活性，造成細胞週期停止。在Fascaplysin的處理下觀察到Hypoxia-induction factor-1α(Hif-1α)蛋白質累積的現象，但不影響c-Myc的蛋白質總量，進一步的分析發現Fascaplysin藥劑處理下對於Hif-1α蛋白質在Pro564位置的hydroxylation程度沒有顯著影響，而Hif-1α蛋白質生成總量上升，顯示Hif-1α的累積可能是因為蛋白質生成總量上升，而不是透過其分解的途徑受到抑制，此結果顯示Cdk4/cyclin D1 complex的活性參與在Hif-1α蛋白質的調控中，正常的Cdk4/cyclin D complex活性抑制Hif-1α累積，使得Hif-1α不會干擾c-Myc的作用，影響細胞生長的進行。研究中發現Fascaplysin除了影響Hif-1α蛋白質生成總量外，也造成S6K與β-Tublin蛋白質總量受到影響，推測Cdk4/cyclin D1 complex活性可能參與調控mRNA到蛋白質生成的層次，影響蛋白質生成的選擇性。另一方面Fascaplysin處理造成eIF-2α的磷酸化上升，可能造成translation initiation的效率降低，影響蛋白質合成速率。本實驗透過探討Cdk4/cyclin D1 complex活性抑制劑Fascaplysin對於細胞生長訊息網絡的影響，顯示Cdk4/cyclin D1 complex活性除了過去所知G1-S transition的角色之外，其活性可能也參與在細胞生長的代謝重整、粒線體生成以及蛋白質合成的調控機制中，擁有促進細胞生長的功能。

關鍵字

Cdk4/cyclin D1 complex ；細胞生長； Fascaplysin ； Hif-1α ； c-Myc ；代謝重整

並列摘要

Cell proliferation is driven by cell growth. During cell growth, cells upregulate macromolecular synthesis and thereby increase in size and mass. In order to rapidly accumulate biomass, cells must engage in the metabolic reprogramming. Growth factors and nutrients activate various signal transduction pathways ,and finally upregulate PI3K/AKT/mTOR pathway signaling. During cell growth, mTORC1-4EBP pathway up-regulates c-Myc protein translation. C-Myc assists PI3K/AKT/mTOR pathway in promoting mitochondria metabolic reprogramming and Warburg effect. C-Myc also promotes mitochondria biogenesis through it effects on downstream targets. Hif-1α inhibits c-Myc function by various mechanisms. By the effect on metabolic reprogramming and mitochondria biogenesis, Hif-1α decreases cell growth activity. But Hif-1α expression also under mTORC1-4EBP pathway control, so Hif-1α must be degradated by PHD system during cell growth. PHD system can respond mitochondria’s status, and normal mitochondria activity can maintain PHD activity. During cell growth Hif-1α is continuously expressed and then degradated through PHD regulation. Cdk4/cyclinD1 complex is also the important molecular during cell growth, and cyclin D1 expression also under mTORC1-4EBP pathway control. In the past, the function of Cdk4/cyclinD1 complex mainly focuses on the role of G1-S transition. Cdk4/cyclinD1 complex promotes cell cycle progression via the well characterized Rb/E2F pathway. But some studies show that Cdk4-cyclinD1 complex induces cell transformation by promoting cell growth rather than Rb/E2F pathway. In Drosophila melanogaster, the function of Cdk4-cyclinD complex in promoting cell growth needs Hph(Drosophila PHD). This result shows that Cdk4/cyclinD1 complex might involves in c-Myc and Hif-1α interrelationship. In human embryonic fibroblast WI38 cells, the Cdk4/cyclin D1 complex activity inhibitor, Fascaplysin induced cell cycle arrest. Fascaplysin induced Hif-1α accumulation, and not interfered c-Myc protein level. Hif-1α accumulation not by decreased the hydroxylation at Pro-564 of Hif-1α, but might through enhanced Hif-1α protein production. These observations show that Cdk4/cyclin D1 complex activity may involves in regulation of Hif-1α protein level. Normal Cdk4/cyclin D1 complex activity assists growth functions of c-Myc by preventing Hif-1α accumulation. We also found that Fascaplysin interfered with the protein levels of S6K and β-Tublin. These results suggest a mechanistic link between Cdk4/cyclin D1 complex activity and regulation of protein levels which involve in cell growth. Fascaplysin treatment increases eIF-2α phosphorylation. This result may decreases protein translation initiation activity, in addition of protein synthesis. In this study, we explore the role of Cdk4/cyclin D1 complex activity during cell growth by using Cdk4/cyclin D1 complex activity inhibitor, Fascaplysin. These results show that Cdk4/cyclin D1 complex activity may have effects in metabolic reprogramming and mitocindria biogenesis through regulation of Hif-1α, and also involve in protein synthesis. Through these functions, Cdk4/cyclin D1 complex can promote cell growth progression.

並列關鍵字

Cdk4/cyclin D1 complex ； Cell growth ； Fascaplysin ； Hif-1α ； c-Myc ； Metabolic reprogramming

參考文獻

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Cdk4-Cyclin D1對於細胞生長之角色探討

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