OS-9 gene is frequently coamplified with CDK4 gene in human sarcomas. We isolated and characterized three isoforms of OS-9 cDNA found in a myeloid leukemia HL-60 cDNA library. Isoform 1 consisted of 2, 700 bp, from which a 667 amino acid sequence was deduced and found to be identical with that of OS-9 cDNA from osteosarcoma cells [Su et al. (1996) Mol. Carcinogen. 15, 270-275]. Isoform 2 cDNA lacked a 165 nucleotide sequence in the coding region. Isoform 3 cDNA had an additional 45 bp deletion in the coding region. Isoforms 2 and 3 encode 612 and 597 amino acid polypeptides, respectively. Comparison of their cDNA sequences with the genomic structure indicated that three isoforms are splice variants. Reverse transcription-polymerase chain reaction analysis showed predominant expression of isoform 2 mRNA in myeloid leukemia HL-60 cells, osteosarcoma OsA-CL cells and rhabdomyosarcoma Rh30 cells. Northern blotting revealed similar levels of expression of OS-9 gene in various tumor cell lines of sarcoma cells, carcinoma cells and myeloid leukemia cells, but 3-4 times higher expression in OsA-CL cells and Rh30 cells containing a homogeneously staining region of 12q13-15. OS-9 expression decreased in differentiation-induced HL-60 cells. Possible involvement of the OS-9 gene in cell growth is discussed.
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