Grp75, also known as mortalin, is a member of Hsp70 family of chaperone proteins that is not heat-inducible. This protein is essential for transporting many mitochondrial proteins from the cytoplasm to mitochondria. Grp75 inactivates the tumor suppressor p53. Studies found that Grp75 is overexpressed in many tumor tissues and immortalized human cell lines, suggesting its role in the tumor formation. Grp75 is also implicated in cell aging, as its overexpression appears to prolong the life span of human fibroblasts.