Small mitochondrial ARF (smARF) is located in both the nucleus and cytoplasm, induces cell death, and activates p53 in mouse fibroblasts

The ARF transcript produces two proteins, the full‐length ARF, p19 ARF , and a short mitochondrial version, smARF. To explore the functional difference between the two, we generated GFP‐fused expression vectors for each protein and introduced them into NIH3T3 murine fibroblasts, which sustains a global deletion in the INK4a locus but contains a functional p53 gene. GFP‐p19 ARF was located within the nucleolus as previously reported, whereas GFP‐smARF was detected mainly in the nucleoplasm. GFP‐smARF induced cell death although to a slightly lesser extent than p19 ARF . GFP‐smARF stabilized p53 thereby inducing expression of the target genes, MDM2 and p21. We suggest that smARF has functions other than mitochondria‐mediated autophagy, and induces p53 expression and cell death via a novel mechanism.