Yu R, Ren S G, Horwitz G A, Wang Z, Melmed S
Division of Endocrinology, Cedars-Sinai Research Institute-UCLA School of Medicine, Los Angeles, California 90048, USA.
Mol Endocrinol. 2000 Aug;14(8):1137-46. doi: 10.1210/mend.14.8.0501.
The pituitary transforming gene, PTTG, is abundantly expressed in endocrine neoplasms. PTTG has recently been recognized as a mammalian securin based on its biochemical homology to Pds1p. PTTG expression and intracellular localization were therefore studied during the cell cycle in human placental JEG-3 cells. PTTG mRNA and protein expressions were low at the G1/S border, gradually increased during S phase, and peaked at G2/M, but PTTG levels were attenuated as cells entered G1. In interphase cells, wild-type PTTG, an epitope-tagged PTTG, and a PTTG-EGFP conjugate all localized to both the nucleus and cytoplasm, but in mitotic cells, PTTG was not observed in the chromosome region. PTTG-EGFP colocalized with mitotic spindles in early mitosis and was degraded in anaphase. Intracellular fates of PTTG-EGFP and a conjugate of EGFP and a mutant inactivated PTTG devoid of an SH3-binding domain were observed by real-time visualization of the EGFP conjugates in live cells. The same cells were continuously observed as they progressed from G1/S border to S, G2/M, and G1. Most cells (67%) expressing PTTG-EGFP died by apoptosis, and few cells (4%) expressing PTTG-EGFP divided, whereas those expressing mutant PTTG-EGFP divided. PTTG-EGFP, as well as the mutant PTTG-EGFP, disappeared after cells divided. The results show that PTTG expression and localization are cell cycle-dependent and demonstrate that PTTG regulates endocrine tumor cell division and survival.
垂体转化基因（PTTG）在内分泌肿瘤中大量表达。基于其与Pds1p的生化同源性，PTTG最近被认为是一种哺乳动物分离酶抑制蛋白。因此，在人胎盘JEG - 3细胞的细胞周期中研究了PTTG的表达和细胞内定位。PTTG mRNA和蛋白表达在G1/S边界处较低，在S期逐渐增加，并在G2/M期达到峰值，但随着细胞进入G1期，PTTG水平减弱。在间期细胞中，野生型PTTG、一个表位标记的PTTG和一个PTTG - EGFP共轭物均定位于细胞核和细胞质，但在有丝分裂细胞中，在染色体区域未观察到PTTG。PTTG - EGFP在有丝分裂早期与有丝分裂纺锤体共定位，并在后期降解。通过实时可视化活细胞中的EGFP共轭物，观察了PTTG - EGFP以及EGFP与缺乏SH3结合结构域的突变失活PTTG的共轭物的细胞内命运。当相同的细胞从G1/S边界进展到S期、G2/M期和G1期时，对其进行连续观察。大多数表达PTTG - EGFP的细胞（67%）通过凋亡死亡，很少有表达PTTG - EGFP的细胞（4%）分裂，而那些表达突变型PTTG - EGFP的细胞则分裂。细胞分裂后，PTTG - EGFP以及突变型PTTG - EGFP消失。结果表明，PTTG的表达和定位是细胞周期依赖性的，并证明PTTG调节内分泌肿瘤细胞的分裂和存活。
