Human major HSP70 protein complements the localization and functional defects of cytoplasmic mutant SV40 T antigen in Swiss 3T3 mouse fibroblast cells.

Abstract

The CT3 cytoplasmic localization mutant of SV40 T antigen is neither properly transported to the nucleus nor is it functional in rodent cells. Human precrisis cells are able to complement this mutation, as they are fully transformed by CT3 with wild-type efficiency. The human-specific factors responsible for this species-specific difference in response to CT3 were localized to human chromosome 6 by synteny in a panel of six somatic cell hybrids. A major human HSP70 heat shock protein located on chromosome 6 is expressed constitutively in human cells. Hsp70 proteins have been reported to play a role in intracellular movement of newly synthesized proteins. To test whether human HSP70 played a role in the complementation by human cells of the defect of CT3, we constructed a series of mouse cell lines expressing human HSP70 and tested them for their ability to localize CT3 T antigen in the nucleus and for their ability to be transformed by CT3 DNA. Mouse cell lines expressing human HSP70 protein were able to translocate mutant CT3 T antigen into the nucleus and were transformed by CT3 at rates comparable with wild-type SV40. Mouse-inducible HSP70 protein was not able to translocate cytoplasmic T antigen in Swiss 3T3 mouse fibroblast cells, even after heat shock. Apparently human HSP70 is capable of complementing directly or indirectly the structural and functional alterations in SV40 T antigen introduced by the CT3 mutation.

Heat-shock protein 70 exerts opposing effects on Vpr-dependent and Vpr-independent HIV-1 replication in macrophages

“…48 Intriguingly, Hsp70 stimulates nuclear import and replication in macrophages of a Vpr-deficient HIV-1. This effect is consistent with the capacity of Hsp70 to stimulate nuclear import of weak karyophiles 23 and suggests that Vpr and Hsp70 might enhance HIV-1 nuclear import through a similar mechanism. In particular, Vpr, similar to the effect of Hsp70, may enhance karyophilic properties of weak NLSs present in the matrix protein, 49 thus stimulating nuclear import of the HIV-1 PIC.…”

“…In particular, Hsp70 was shown to facilitate the interaction between the basic type NLS and importin ␣. 21,22 The ectopic expression of human Hsp70 in mouse cells complemented the defective import of a mutant simian virus 40 (SV40) large T antigen, 23 and the depletion of Hsp70 from cytosolic extracts prevented import. 24,25 In addition, our recent studies demonstrated that Hsp70 stimulates nuclear import of the HIV-1 PIC in a cell-free in vitro assay.…”

A Nuclear Export Signal Prevents Saccharomyces cerevisiae Hsp70 Ssb1p from Stimulating Nuclear Localization Signal-directed Nuclear Transport

“…Role of the Hsp70 Chaperone System in NLS-directed Nuclear Transport-Molecular genetic evidence supports the notion that Hsp70 facilitates the formation and stability of the NLS-Kap ␣ complex (15,16). Cell biological evidence indicates that Hsp70 is co-imported with the NLS-cargo-Kap ␣/␤ ternary complex (19,46).…”

“…1, 14, and 15). Thus, the ectopic expression of human Hsp70 in mouse cells rescued the import of a protein carrying a mutant NLS (16). Conversely, the elevated expression of SSA1 in yeast suppressed a transport defect in srp1-31 cells (15).…”

p53-independent association between SV40 large T antigen and the major cytosolic heat shock protein, HSP90

“…HSP70 is reported to a ect the structure of LT, and to complement the localization and functional defects of a LT mutant (Jeoung et al, 1991). HSP90 is also reported to a ect the conformation of several substrate proteins (Miyata and Yahara, 1992;Shaknovich et al, 1992;Wiech et al, 1992).…”