Apoptosis and appearance of Trp53-positive micronuclei in murine tumors with different radioresponses in vivo.
The purpose of this paper is to determine the relationship between the response to radiation and the appearance of apoptosis and micronuclei with Trp53 protein in murine tumors after irradiation. Two murine tumors, EL4, which was derived from a mouse lymphoma, and FM3A, which was derived from a mouse mammary carcinoma, were locally irradiated with 15 Gy and sections were stained with H&E and an anti-Trp53 antibody. The response to radiation was greater in EL4 tumors than in FM3A tumors. The frequency of apoptotic cells in EL4 tumors was 6.1 +/- 1.2% at time zero, reached a peak of 36.3 +/- 3. 8% at 6 h, and then decreased with time through 72 h to 2.5 +/- 1.5% after 15 Gy irradiation. In FM3A tumors, no apoptotic cells were detected at 0, 1, 3, 6 or 24 h after exposure. At 48 and 72 h, the frequency was only 3.0 +/- 0.6% and 1.3 +/- 0.3%. Apoptotic cells increased significantly at 3, 6 and 24 h after irradiation in EL4 tumors (P < 0.008) and at 48 and 72 h in FM3A tumors (P < 0.006). The frequency of Trp53-positive cells was 17.9 +/- 2.2 and 15.2 +/- 2.3% at time zero in EL4 and FM3A tumors, respectively, increased to 74.5 +/- 4.5% in EL4 cells (P = 0.001), and increased to 33.9 +/- 1. 1% in FM3A cells (P = 0.005) 1 h after irradiation. Trp53-positive micronuclei appeared in cells in both tumors from 24 to 72 h after irradiation. The frequency of Trp53-positive micronuclei was 3.8 +/- 0.5 and 13.5 +/- 1.3% at 24 h in EL4 and FM3A tumors, respectively, and gradually decreased by 72 h. After exposure to 15 Gy, Trp53-positive micronuclei increased significantly in FM3A tumors compared to EL4 tumors at both 24 and 48 h (P < 0.02). The frequency of these micronuclei increased with increasing dose in FM3A tumors, and the difference between these percentages after 3 Gy and after 5, 10 and 15 Gy was significant (P < 0.02). Many apoptotic cells were observed in the radiosensitive EL4 tumor after irradiation. Death by apoptosis may be related to an early response to radiation in these tumors. The appearance of micronuclei may be an important mechanism of cell death in FM3A tumors in which no apoptosis was induced.
Saito
Y
Y
Department of Radiology and Radiation Oncology, Gunma University School of Medicine, Maebashi, Gunma 371, Japan.
Mitsuhashi
N
N
Sakurai
H
H
Ishikawa
H
H
Hasegawa
M
M
Akimoto
T
T
Hayakawa
K
K
Niibe
H
H
D000818:Animals; D017209:Apoptosis / Q000528:radiation effects*; D051379:Mice; D048629:Micronuclei, Chromosome-Defective / Q000378:metabolism*; D008938:Mitosis / Q000528:radiation effects; D009374:Neoplasms, Experimental / Q000378:metabolism* / Q000503:physiopathology; D011836:Radiation Tolerance; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
D016159:Tumor Suppressor Protein p53