Simian Virus 40 Large T Antigen J Domain and Rb-Binding Motif Are Sufficient To Block Apoptosis Induced by Growth Factor Withdrawal in a Neural Stem Cell Line

Abstract

Serum-free mouse embryo (SFME) cells are a neural stem cell line that is dependent upon epidermal growth factor (EGF) for survival. Removal of EGF results in the G1 arrest and apoptosis of SFME cells. We have shown that the expression of simian virus 40 large T antigen in SFME cells blocks apoptosis and allows cell survival and division in the absence of EGF. Therefore the presence of T antigen abrogates the EGF requirement. The steady-state levels of p53, p21, and mdm-2 do not increase as SFME cells undergo apoptosis upon EGF withdrawal. Furthermore, the amino-terminal 136 amino acids (N136) of T antigen are sufficient to block death and to promote proliferation in the absence of EGF, while the carboxy-terminal fragment (C251–708), which contains the p53 binding site, is unable to block death. Taken together, these data suggest that SFME cells deprived of EGF undergo p53-independent apoptosis. Mutations that disrupt either the J domain or Rb family binding abolish the ability of T antigen to block SFME cell apoptosis and to promote cell growth. We conclude that T antigen must act on one or more members of the Rb family to inhibit SFME cell apoptosis.

Rb binding protein Che-1 interacts with Tau in cerebellar granule neurons

“…Two distinct portions of Che-1 protein have been described to mediate interaction with retinoblastoma gene product (Rb) (Fanciulli et al, 2000), and here we show that two other distinct portions of Che-1 protein mediate interaction with Tau. Significantly, Myc-Che-1B, located in the amino terminal, contains a relevant homology with the "J domain" of SV40 large T, that was defined to be sufficient to block apoptosis, induced by growth factor withdrawal, in a neuronal stem cell line (Slinskey et al, 1999). Myc-Che-1E is located in the carboxyl terminal half of the molecules and it is characterized by an elevated number of leucine residues.…”

Episomal vectors for gene expression in mammalian cells

“…Furthermore, it has been shown that BKV is mutagenic in human cells and that BKV T antigen induces chromosomal aberrations in human embryonic fibroblasts. Studies with SV40 large T antigen, which has high sequence and function homology with BKV T antigen, indicate that the large T antigen influences cellular gene expression by altering mRNA levels of cellular transcription factors, but also by interacting with and regulating the DNA‐binding or transcriptional activity of specific transcription factors [180–186]. Therefore, further improvement of these vectors has mainly focused on the elimination of the T antigen.…”

The Molecular Chaperone Activity of Simian Virus 40 Large T Antigen Is Required To Disrupt Rb-E2F Family Complexes by an ATP-Dependent Mechanism

“…The D44N point mutation lies in the strictly conserved HPD loop that is critical for J protein function and is conserved among T antigens of all polyomaviruses (33). We showed previously that this mutant is defective for replication, inhibition of apoptosis, and partially defective for transformation (32,40,42). When added to the lysate expressing the p130-E2F-4 complex, D44N coprecipitated p130 and E2F-4 as well as wildtype T antigen ( Fig.…”

“…We have previously shown that T antigen requires a functional J domain and Rb binding motif in cis to transform REF52 and C3H10T1/2 cells (42). Both the J domain and pRb binding motif are also required for T-antigen-mediated inhibition of apoptosis (40). Furthermore, both the J domain and pRb binding motif are required for T antigen to alleviate pRb-mediated inhibition of E2F transactivation (19,39,47).…”