CDK4-CyclinD在細胞生長中對代謝重組角色之探討

Abstract

生命的延續建築在細胞複製的忠實性(Fidelity)上，因此細胞對於細胞生長的機制勢必會有精密的調控。當細胞進行增生時會發生旺盛的代謝重組 (Metabolic reprogramming) ，包含Warburg effect和Glutamine-dependent anaplerosis兩種現象，並且透過PI3K/AKT/mTOR pathway。當細胞受到生長因子刺激時， mechanistics target of rapamycin complex 1 (mTORC1) 可以使Hypoxia induce factor-1α (HIF-1α) 和c-Myc大量表現，進而促進代謝重組。在果蠅的研究中指出，CDK4-cyclin D complex會透過 Prolyl hydroxylase (PHD) 系統影響細胞生長，另外的研究指出，PHD3會對Pyruvate kinase M2 isoform (PKM2) 進行hydroxylation，使得PKM2 recruit HIF-1α到Hypoxia response elements (HREs) 上，表現更多的PKM2和PHD3，對此路徑形成正迴饋的訊號放大。本實驗對HeLa細胞處理CDK4-cyclin D complex活性抑制劑Fascaplysin來探討CDK4-cyclin D complex對於細胞生長之調控，結果顯示CDK4-cyclin D complex除了導致c-Myc表現量上升外，還透過轉譯調控來促進PHD3、HIF-1α的蛋白質表現量。 c-Myc表現量上升能使得Anaplerosis大量活化，導致mTORC1能夠維持活性，同時造成抑制mTORC2的活性，PHD3和HIF-1α的表現量上升可能去促進PKM2的hydroxylation和對於HREs目標基因的表現，形成一正迴饋迴路放大PHD3和PKM2，進而促進代謝重組而影響細胞生長。

The mechanism of cell growth is strictly regulated.Two phenomena of metabolic reprogramming are involved in cell growth, including Warburg effect and Glutamine-dependent anaplerosis, which are regulated by PI3K/AKT/mTOR pathway. Under growth factors stimulation, cellular protein levels of Hypoxia induce factor-1α (HIF-1α) and c-Myc are massively increased by mechanistics target of rapamycin complex 1 (mTORC1). Our data show that CDK4-cyclin D complex increases protein level of c-Myc. Furthermore, our results demonstrate that increased c-Myc causes activation of anaplerosis that sustains the activity of mTORC1 but not that of mTORC2. In Drosophila studies, it has been shown that the promotion of cell growth by CDK4-cyclin D complex is mediated through Prolyl hydroxylase (PHD). A recent study demonstrated that hydroxylation of Pyruvate kinase M2 isoform (PKM2) by PHD3 enhances recruitment of HIF-1α to hypoxia response elements (HREs) and results in increased expression of PKM2 and PHD3. Consistently, our study shows that treatment with Fascaplysin, the inhibitor of CDK4-cyclin D complex, decreases the protein level of PHD3 in HeLa cell. It appears that PHD3 is involved in the hydroxylation of PKM2, which leads to the positive feedback to protein level of PHD3 and promotes metabolic reprogramming in cell growth.