School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, Tokyo, Japan.
Biol Pharm Bull. 2010;33(1):35-9. doi: 10.1248/bpb.33.35.
We previously demonstrated that FGD1, the Cdc42 guanine nucleotide exchange factor (GEF) responsible for faciogenital dysplasia, and its homologue FGD3 are targeted by the ubiquitin ligase SCF(FWD1) upon phosphorylation of two serine residues in their DSGIDS motif and subsequently degraded by the proteasome. FGD1 and FGD3 share highly homologous Dbl homology (DH) and adjacent pleckstrin homology (PH) domains, both of which are responsible for GEF activity. However, their function and regulation are remarkably different. Here we demonstrate extracellular signal-responsive translocation of FGD1, but not FGD3. During the wound-healing process, translocation of FGD1 to the leading edge membrane occurs in cells facing to the wound. Furthermore, epidermal growth factor (EGF) stimulates the membrane translocation of FGD1, but not FGD3. As the most striking difference, FGD3 lacks the N-terminal proline-rich domain that is conserved in FGD1, indicating that proline-rich domain may play a crucial role in signal-responsive translocation of FGD1. Indeed, there is a faciogenital dysplasia patient who has a missense mutation in proline-rich domain of FGD1, by which the serine residue at position 205 is substituted with isoleucine. When expressed in cells, the mutant FGD1 with S(205)/I substitution fails to translocate to the membrane in response to the mitogenic stimuli. Thus we present a novel mechanism by which the activity of FGD1, a GEF for Cdc42, is temporally and spatially regulated in cells.
我们之前已经证明，FGD1（负责面-生殖器发育不良的 Cdc42 鸟嘌呤核苷酸交换因子（GEF））及其同源物 FGD3 在其 DSGIDS 基序中的两个丝氨酸残基磷酸化后被泛素连接酶 SCF（FWD1）靶向，并随后被蛋白酶体降解。FGD1 和 FGD3 共享高度同源的 Dbl 同源（DH）和相邻的 pleckstrin 同源（PH）结构域，这两个结构域都负责 GEF 活性。然而，它们的功能和调节机制却截然不同。在这里，我们证明了 FGD1 可进行细胞外信号响应性转位，但 FGD3 不能。在伤口愈合过程中，面向伤口的细胞中 FGD1 向前缘膜的转位发生。此外，表皮生长因子（EGF）刺激 FGD1 的膜转位，但不刺激 FGD3。最显著的区别是，FGD3 缺乏 FGD1 中保守的 N 端富含脯氨酸结构域，这表明富含脯氨酸的结构域可能在 FGD1 的信号响应性转位中发挥关键作用。事实上，有一位面-生殖器发育不良的患者在 FGD1 的富含脯氨酸结构域中存在一个错义突变，该突变使位置 205 的丝氨酸残基被异亮氨酸取代。当在细胞中表达时，具有 S（205）/I 取代的突变 FGD1 无法响应有丝分裂刺激而转位到膜上。因此，我们提出了一种新的机制，通过该机制，细胞中 Cdc42 的 GEF FGD1 的活性被时空调节。
