Tahmasebi Soroush, Ghorbani Mohammad, Savage Paul, Gocevski Goran, Yang Xiang-Jiao
The Rosalind & Morris Goodman Cancer Research Center, Montréal, Québec, Canada; Department of Anatomy & Cell Biology, Montréal, Québec, Canada.
Stem Cells. 2014 Apr;32(4):1012-20. doi: 10.1002/stem.1600.
Sumoylation adds a small ubiquitin-like modifier (SUMO) polypeptide to the ε-amino group of a lysine residue. Reminiscent of ubiquitination, sumoylation is catalyzed by an enzymatic cascade composed of E1, E2, and E3. For sumoylation, this cascade uses Ubc9 (ubiquitin conjugating enzyme 9, now officially named ubiquitin conjugating enzyme E2I [UBE2I]) as the sole E2 enzyme. Here, we report that expression of endogenous Ubc9 increases during reprogramming of mouse embryonic fibroblasts (MEFs) into induced pluripotent stem (iPS) cells. In addition, this E2 enzyme is required for reprogramming as its suppression dramatically inhibits iPS cell induction. While Ubc9 knockdown does not affect survival of MEFs and immortalized fibroblasts, Ubc9 is essential for embryonic stem cell (ESC) survival. In addition, we have found that Ubc9 knockdown stimulates apoptosis in ESCs but not in MEFs. Furthermore, the knockdown decreases the expression of the well-known pluripotency marker Nanog and the classical reprogramming factors Klf4, Oct4, and Sox2 in ESCs. Together, these observations indicate that while dispensable for fibroblast survival, the sole SUMO E2 enzyme Ubc9 plays a critical role in reprogramming fibroblasts to iPS cells and maintaining ESC pluripotency.
SUMO化修饰是将一个小的类泛素修饰物（SUMO）多肽添加到赖氨酸残基的ε-氨基上。与泛素化类似，SUMO化修饰由E1、E2和E3组成的酶促级联反应催化。对于SUMO化修饰，该级联反应使用Ubc9（泛素缀合酶9，现正式命名为泛素缀合酶E2I [UBE2I]）作为唯一的E2酶。在此，我们报道在小鼠胚胎成纤维细胞（MEF）重编程为诱导多能干细胞（iPS）的过程中，内源性Ubc9的表达增加。此外，这种E2酶对于重编程是必需的，因为其抑制会显著抑制iPS细胞的诱导。虽然敲低Ubc9不影响MEF和永生化成纤维细胞的存活，但Ubc9对胚胎干细胞（ESC）的存活至关重要。此外，我们发现敲低Ubc9会刺激ESC凋亡，但不会刺激MEF凋亡。此外，敲低会降低ESC中著名的多能性标志物Nanog以及经典重编程因子Klf4、Oct4和Sox2的表达。总之，这些观察结果表明，虽然对成纤维细胞存活不是必需的，但唯一的SUMO E2酶Ubc9在将成纤维细胞重编程为iPS细胞以及维持ESC多能性方面起着关键作用。
