INDUCTION OF CELLULAR SENESCENCE BY TRANSFECTION OF CYTOSOLIC MORTALIN CDNA IN NIH-3T3-CELLS

We have recently identified a novel member of hsp70 family (mortalin) as a mortality marker (Wadhwa, R., Kaul, S. C., Ikawa, Y., and Sugimot o, Y. (1993) J. Biol. Chem. 268, 6615-6621). It has distinct intracell ular distribution in mortal and immortal fibroblasts. Here, we report that the cytosolic (mot-1) and the perinuclear (mot-2) forms of mortal in cDNA cloned from mortal and immortal cells, respectively, differ by only two bases in the open reading frame, resulting in two amino acid changes. The induced expression of the cytosolic form by transfection of mot-1 cDNA (isolate from CD1-ICR mouse embryonic fibroblasts) to N IH 3T3 cells induced cellular senescence. However, the perinuclear for m expressed by mot-2 cDNA (isolate from NIH 3T3 cells) did not yield a n equivalent effect. The data suggest the senescence-inductive functio n of cytosolic mortalin and implicitly point to a genetic event involv ed in immortalization.