Agarwal M L, Agarwal A, Taylor W R, Chernova O, Sharma Y, Stark G R
Department of Molecular Biology, Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA.
Proc Natl Acad Sci U S A. 1998 Dec 8;95(25):14775-80. doi: 10.1073/pnas.95.25.14775.
Normal mammalian cells arrest primarily in G1 in response to N-(phosphonacetyl)-L-aspartate (PALA), which starves them for pyrimidine nucleotides, and do not generate or tolerate amplification of the CAD gene, which confers resistance to PALA. Loss of p53, accompanied by loss of G1 arrest, permits CAD gene amplification and the consequent formation of PALA-resistant colonies. We have found rat and human cell lines that retain wild-type p53 but have lost the ability to arrest in G1 in response to PALA. However, these cells still fail to give PALA-resistant colonies and are protected from DNA damage through the operation of a second checkpoint that arrests them reversibly within S-phase. This S-phase arrest, unmasked in the absence of the G1 checkpoint, is dependent on p53 and independent of p21/waf1.
正常哺乳动物细胞在N-（膦酰乙酰基）-L-天冬氨酸（PALA）作用下主要停滞在G1期，PALA使细胞缺乏嘧啶核苷酸，且正常细胞不会产生或耐受CAD基因的扩增，CAD基因赋予细胞对PALA的抗性。p53缺失并伴随G1期停滞丧失时，会使CAD基因扩增并导致产生对PALA耐药的集落。我们发现大鼠和人类细胞系保留了野生型p53，但丧失了在PALA作用下停滞在G1期的能力。然而，这些细胞仍然不能产生对PALA耐药的集落，并且通过第二个检查点的运作受到保护而免受DNA损伤，该检查点使它们在S期内可逆性停滞。这种在没有G1检查点时才显现的S期停滞依赖于p53且不依赖于p21/waf1。
