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Levine等人最早在研究SV40 large T antigen的致癌機轉時,發現large
T antigen 在細胞中可和ㄧ個蛋白質結合,其分子量為53KDa,故命名為
p53.其基因後來被証實是ㄧ種腫瘤抑制基因.而p53在人類癌症中,扮演著
極重要的角色.有相當高比例的癌細胞中皆有p53突變的情形產生,若將原
型p53 (wild-type)導入癌細胞中,常可抑制癌細胞生長及癌化現象.由於
當將大量 p53導入癌細胞時,可將細胞停滯在G1期,所以p53可能和細胞週
期有關.最近的研究又顯示,當DNA受損時會誘發p53的產生,而再表現ㄧ群
GADD(growth arrest,DNA damage inducible)基因去延滯細胞週期的進
行,以等待DNA的修補.所以p53和細胞由停滯期(G0)進入G1期的轉變有某種
關係存在. 我們將COS-1及B104-1-1二種細胞株以0.1%血清培養48小時,使
細胞進入G0期,而後加入20%血清刺激使細胞由G0進入G1期.利用anti-p53
之抗體測定這段時期中細胞核內p53蛋白質量之改變.結果顯示在COS-1細
胞中,p53之量隨著 serum starvation時間增加而增加,而當加入血清後30
分鐘,p53更產生ㄧ個短暫性高峰而後下降的情形.為確定出現此ㄧ短暫性
p53高峰之原因,我們進ㄧ步測定完整細胞,細胞質,及細胞核內p53之含量,
結果顯示細胞核內p53量增加,而細胞質內p53量減少,因此推測此現象可能
是p53由細胞質往細胞核運送所造成的.但在另ㄧ細胞株B104-1-1中,我們
則未觀察到此ㄧ現象.進ㄧ步,我們設計利用反順序oligonucleotides去抑
制此ㄧp53之短暫性高峰,但不論是利用部分修飾(thio-ester 飾之
oligonucleotides ,皆無法有效抑制p53的產生.
The wild-type p53 gene is defined as a tumor suppressor gene.
The p53 is a 53KDa protein which was first detected in SV40-
tran- sformed cells in a complex with the SV40 large T antigen.
The p53 gene was frequently found to be mutated in a wide
variety of human tumors;whereas wild-type p53 actively inhibits
transform- ation. It may play a very important role in
tumorigensis. Biologically,transformed cells transfected with
the wild-type p53 gene were arrested in the G1 phase of cell
cycle.Recent evidences suggested that DNA damage caused a rise
in the levels of the p53 protein, then induced the expression
of GADD gene to arrest cell cycle progression for DNA repair.
P53 may also be related with the transition from G0 to G1. In
order to study the role of p53 in the transition from G0 to G1,
we measured the level of nuclear p53 protein during serum
starvation and after serum restimulation . COS-1 cells and
B104-1-1 cells were serum starved for 48 hours and restimulated
to enter G1 phase by adding 20%F.C.S. In COS-1 cells ,the level
of nuclear p53 protein increased gradually during starvation
period, and rised sharply in the first 30 minutes after serum
restimulation,then declined. To further study the appearance of
transient peak of p53, the levels of p53 in nucleus,cytosol,and
in whole cell were measured. We found the level of p53 protein
increased in nucleus,and decreased in cytosol. The results
indicated that the appearance of this peak was primarily due to
nuclear translocation. While in B104-1-1 cells, the phenomenon
was not observed. Antisense oligonucleotide approach has been
used to study the biological significance of this transient
peak;however,both partial and complete thio- -modified anti-p53
oligonucleotides were ineffective to block the expression of
p53 in COS-1 cells.
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