表現於粒線體基質之Mcl-1異形體的功能性探討

Abstract

Mcl-1是Bcl-2蛋白家族的一員，它最主要的功能在於抵抗細胞凋亡的發生。先前的研究已經發現在跑蛋白電泳時，Mcl-1 會出現大小不同的兩條分子片段，而這兩條分子片段在我們實驗室先前的結果中證實泳動速率較慢的Mcl-1異形體主要位在粒線體的外膜上，然而泳動速率較快的異形體則是會進到粒線體的基質當中。更進一步的，我們發現位在粒線體外膜的Mcl-1是主要具有抗細胞凋亡功能的異形體；而位在粒線體基質的Mcl-1異形體則沒有這樣的功能。直到最進，Perciavalle等人的研究指出，位在粒線體基質的Mcl-1異形體在調控生物能量轉換的過程扮演重要的角色。然而它是透過什麼樣的機制作用目前仍不得而知。在這篇研究中，我們製造出一種Mcl-1的基因突變鼠（3RG突變鼠），在這些基因突變鼠中，Mcl-1沒有辦法產生位於粒線體基質的異形體。令人意外的是，這些3RG突變鼠的出生符合孟德爾遺傳定律並且可以正常的生長發育且外觀無明顯異常。除此之外，我們的實驗數據顯示和先前發表的報導相反的結果：缺少Mcl-1粒線體基質異形體的小鼠胚胎纖維母細胞和控制組相比有類似的細胞生長速率、氧氣消耗率以及腺苷三磷酸產量 (ATP)。更進一步的研究發現，無論是在正常情形或是曝露在寒冷的環境後，3RG突變鼠的骨骼肌組織中含有的腺苷三磷酸量 (ATP) 相較於控制組有些微減少的趨勢，這個結果可能顯示位在粒線體基質的Mcl-1異形體只在特定的組織中調控生物能量的代謝。

Mcl-1 is a member of Bcl-2 protein family. The well-known function of Mcl-1 is its ability to antagonize cell apoptosis. Previous studies have shown that when proteins are subjected to electrophoresis, Mcl-1 appears as a doublet. Earlier works done in our lab indicates that the slow mobility isoform of Mcl-1 localizes to mitochondria outer membrane whereas the fast mobility isoform exclusively to the mitochondria matrix. Moreover, we showed that the outer membrane-localized isoform is the one that contributes to the anti-apoptosis activity of Mcl-1 whereas the matrix matrix-localized isoform is devoid of such activity. Recently, Perciavalle et al. (2012) reported that the matrix isoform plays a role in the regulation of cellular bioenergetics. However how matrix-localized Mcl-1 influences the cellular bioenergetics is still a mystery. In this study, we generated a mouse model (the 3RG mutant) that possesses a mutation that lacks the matrix-localized Mcl-1 isoform. Surprisingly, the 3RG mice were born with expected Mendelian frequency, and appeared to be developmentally normal with a gross normal appearance. Moreover, in contrast to what was reported by Perciavalle et al. (2012), 3RG MEFs manifested similar growth rate, oxygen consumption and ATP production as the wild type cells. Further analysis revealed a very minor phenotype in the 3RG mice, that is, their muscle tended to have lower amounts of ATP both under normal and under cold stress conditions. This results support that the matrix isoform of Mcl-1 may regulate cellular bioenergetics in a tissue-specific manner.