Kawahara H, Philipova R, Yokosawa H, Patel R, Tanaka K, Whitaker M
Department of Physiological Sciences, Medical School, University of Newcastle, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK.
J Cell Sci. 2000 Aug;113 ( Pt 15):2659-70. doi: 10.1242/jcs.113.15.2659.
The proteasome has been shown to be involved in exit from mitosis by bringing about destruction of mitotic cyclins. Here, we present evidence that the proteasome is also required for proper completion of S phase and for entry into mitosis in the sea urchin embryonic cleavage cycle. A series of structurally related peptide-aldehydes prevent nuclear envelope breakdown in their order of inhibitory efficacies against the proteasome. Their efficacies in blocking exit from S phase and exit from mitosis correlate well, indicating that the proteasome is involved at both these steps. Mitotic histone HI kinase activation and tyrosine dephosphorylation of p34(cdc2) kinase are blocked by inhibition of the proteasome, indicating that the proteasome plays an important role in the pathway that leads to embryonic p34(cdc2 )kinase activation. Arrested embryos continued to incorporate [(3)H]thymidine and characteristically developed large nuclei. Pre-mitotic arrest can be overcome by treatment with caffeine, a manoeuvre that is known to override the DNA replication checkpoint. These data demonstrate that the proteasome is involved in the control of termination of S phase and consequently in the initiation of M phase of the first embryonic cell cycle.
蛋白酶体已被证明通过促使有丝分裂周期蛋白的降解而参与有丝分裂的退出过程。在此，我们提供证据表明，在海胆胚胎卵裂周期中，蛋白酶体对于S期的正常完成以及进入有丝分裂也是必需的。一系列结构相关的肽醛按照它们对蛋白酶体的抑制效力顺序，可阻止核膜破裂。它们在阻断从S期退出和从有丝分裂退出方面的效力密切相关，表明蛋白酶体在这两个步骤中都发挥作用。蛋白酶体的抑制会阻断有丝分裂组蛋白H1激酶的激活以及p34(cdc2)激酶的酪氨酸去磷酸化，这表明蛋白酶体在导致胚胎p34(cdc2)激酶激活的途径中起重要作用。被阻滞的胚胎继续掺入[(3)H]胸腺嘧啶，并特异地形成大细胞核。用咖啡因处理可以克服有丝分裂前的阻滞，咖啡因是一种已知能绕过DNA复制检查点的操作。这些数据表明，蛋白酶体参与了S期终止的控制，进而参与了第一个胚胎细胞周期M期的起始。
