Pituitary tumor transforming gene (PTTG) regulates placental JEG-3 cell division and survival: evidence from live cell imaging.
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.
Division of Endocrinology, Cedars-Sinai Research Institute-UCLA School of Medicine, Los Angeles, California 90048, USA.
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Yu
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Ren
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Horwitz
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Wang
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Melmed
D000595:Amino Acid Sequence; D002453:Cell Cycle / Q000502:physiology*; D002455:Cell Division / Q000502:physiology; D002470:Cell Survival / Q000502:physiology; D049452:Green Fluorescent Proteins; D006801:Humans; D008164:Luminescent Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D010920:Placenta / Q000166:cytology*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D064249:Securin; D014407:Tumor Cells, Cultured
D008164:Luminescent Proteins; D009363:Neoplasm Proteins; D011994:Recombinant Proteins; D064249:Securin; C578002:pituitary tumor-transforming protein 1, human; D049452:Green Fluorescent Proteins