Targeted inactivation of MLL3 histone H3-Lys-4 methyltransferase activity in the mouse reveals vital roles for MLL3 in adipogenesis
Targeted inactivation of MLL3 histone H3-Lys-4 methyltransferase activity in the mouse reveals vital roles for MLL3 in adipogenesis
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DOI：
10.1073/pnas.0810100105
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发表时间：
2008-12-09
影响因子：
11.1
通讯作者：
Lee, Jae W.
中科院分区：
文献类型：
--
作者：
Lee, Jeongkyung;Saha, Pradip K.;Lee, Jae W.
激活信号协整合因子 2 (ASC-2) 是多种转录因子的转录共激活因子，包括脂肪形成因子过氧化物酶体增殖物激活受体 γ (PPAR γ) 和 C/EBP α，与组蛋白 H3-Lys-4-甲基转移酶 (H3K4MT) MLL3 或其旁系同源物 MLL4 相关，形成名为 ASCOM（ASC-2 复合体）的复合体。事实上，ASC-2 缺失的小鼠胚胎成纤维细胞 (MEF) 已被证明对 PPAR γ 刺激的脂肪生成具有抵抗力，并且无法表达 PPAR γ 响应性脂肪生成标记基因 aP2。然而，MLL3 和 MLL4 在脂肪生成中的具体作用仍不清楚。在这里，我们提供的证据表明 MLL3 在脂肪生成中发挥着至关重要的作用。首先，表达 MLL3 H3K4MT 失活突变体的 MLL3(Delta/Delta) 小鼠的白色脂肪明显减少。其次，MLL3(Delta/Delta) MEF 对脂肪生成诱导剂的反应比 WT MEF 温和但始终较低。第三，ASC-2、MLL3和MLL4在脂肪形成过程中被招募到PPARγ激活的aP2基因，并且PPARγ被证明可以直接与纯化的ASCOM相互作用。此外，虽然aP2的H3K4甲基化在WT MEF中很容易诱导，但在ASC-2(-/-) MEF中不被诱导，并且在MLL3(Delta/Delta) MEF中仅部分诱导。这些结果表明 ASCOM-MLL3 和 ASCOM-MLL4 可能作为 PPAR γ 依赖性脂肪生成的关键但冗余的 H3K4MT 复合物发挥作用。
Activating signal cointegrator-2 (ASC-2), a transcriptional coactivator of multiple transcription factors that include the adipogenic factors peroxisome proliferator-activated receptor gamma (PPAR gamma) and C/EBP alpha, is associated with histone H3-Lys-4-methyltransferase (H3K4MT) MLL3 or its paralogue MLL4 in a complex named ASCOM (ASC-2 complex). Indeed, ASC-2-null mouse embryonic fibroblasts (MEFs) have been demonstrated to be refractory to PPAR gamma-stimulated adipogenesis and fail to express the PPAR gamma-responsive adipogenic marker gene aP2. However, the specific roles for MLL3 and MLL4 in adipogenesis remain undefined. Here, we provide evidence that MLL3 plays crucial roles in adipogenesis. First, MLL3(Delta/Delta) mice expressing a H3K4MT-inactivated mutant of MLL3 have significantly less white fat. Second, MLL3(Delta/Delta) MEFs are mildly but consistently less responsive to inducers of adipogenesis than WT MEFs. Third, ASC-2, MLL3, and MLL4 are recruited to the PPAR gamma-activated aP2 gene during adipogenesis, and PPAR gamma is shown to interact directly with the purified ASCOM. Moreover, although H3K4 methylation of aP2 is readily induced in WT MEFs, it is not induced in ASC-2(-/-) MEFs and only partially induced in MLL3(Delta/Delta) MEFs. These results suggest that ASCOM-MLL3 and ASCOM-MLL4 likely function as crucial but redundant H3K4MT complexes for PPAR gamma-dependent adipogenesis.