p53 Accumulation, defective cell proliferation, and early embryonic lethality in mice lacking tsg101

Functional inactivation of the tumor susceptibility gene tsg101 in NIH 3T3 fibroblasts results in cellular transformation and the ability to form meta static: tumors in nude mice. The N-terminal region of tsg101 protein is str ucturally similar to the catalytic domain of ubiquitin-conjugating enzymes, suggesting a potential role of tsg101 in ubiquitin-mediated protein degrad ation. The C-terminal domain of TSG101 can function as a repressor of trans cription, To investigate the physiological function of tsg101, we generated a null mutation of the mouse gene by gene targeting. Homozygous tsg101-/- embryos fail to develop past day 6.5 of embryogenesis (E6.5), are reduced i n size, and do not form mesoderm. Mutant embryos show a decrease in cellula r proliferation in vivo and in vitro but no increase in apoptosis, Although levels of p53 transcripts were not affected in tsg101-/- embryos, p53 prot ein accumulated dramatically, implying altered posttranscriptional control of p53. In addition, transcription of the p53 effector, cyclin-dependent ki nase inhibitor p21(WAF-1/CIP-1), was increased 5-to 10-fold, whereas activa tion of MDM2 transcription secondary to p53 elevation was not observed. Int roduction of a p53 null mutation into tsg101-/- embryos rescued the gastrul ation defect and prolonged survival until E8.5. These results demonstrate t hat tsg101 is essential for the proliferative burst before the onset of gas trulation and establish a functional connection between tsg101 and the p53 pathway in vivo.