Human mortalin (HSPA9): a candidate for the myeloid leukemia tumor suppressor gene on 5q31

Human mortalin (HSPA9) was originally identified by its close homology to m urine mortalins, which play important roles in cellular senescence. The two murine genes, mot-1 and mot-2, differ in only two amino acid residues, but have opposite functions in cellular immortalization. HSPAS was recently lo calized to chromosome 5, band q31, a region that is frequently deleted in m yeloid leukemias and myelodysplasia (MDS), making it a candidate tumor supp ressor gene, which is consistent with the biological function of its murine homologue. To evaluate mortalin in this capacity, its expression in normal and leukemic cell lines was investigated, and its genomic structure was de termined in order to facilitate mutation detection. RT-PCR and Northern blo t analysis revealed a broad distribution in normal tissues and in leukemia cell lines, producing a single 2.8 kb transcript. Genomic characterization showed that the gene spans 18 kb, and consisted of 17 exons with boundaries that were almost identical to its murine counterpart. Using Intron-based p rimers to flank each exon, sequence of the complete protein-coding regions was obtained for three AML cell lines, including two lines with chromosome 5 loss (KG-1 and HL-60) and one without (AML-193) compared to normal DNA. N o mutations were identified although one conservative nucleotide sequence v ariant was observed in exon 16. We have shown that mortalin is highly conse rved in genomic structure as well as sequence, and the designed primers wil l be suitable for future studies to detect mutations In clinical samples.