Identification and characterization of a novel gene that is upregulated inleukaemia cells by nitric oxide

Nitric oxide (NO) inhibits growth and induces differentiation in acute myel oid leukaemia (AML) cells. To identify genes associated with these processe s, we studied the effect of NO on AML gene expression using the technique o f Representational Difference Analysis. Exposure of HL-60 cells to the NO d onor DETA-NO for 24 h induced the expression of a novel gene that was named rno (regulated by nitric oxide). Treatment of HL-60 cells with dimethyl su lphoxide induced expression of rno, but treatment with Vitamin D-3 or all-t rans retinoic acid did not. Upregulation of rno by NO was cGMP independent. Northern blot analysis indicated that constitutive expression of the novel gene was limited to leucocytes. Three isoforms of rno were identified. An rno cDNA clone was obtained by screening a human leucocyte library. The nuc leotide sequence of the open reading frame shared significant homology with that of the human ribonuclease/angiogenin inhibitor (RI). The predicted am ino acid sequence indicated that, like RI, rno is leucine and cysteine rich and is comprised of a series of repetitive elements (leucine-rich repeats) that may mediate macromolecular interactions. Enhancement of expression of rno may be a component of the process by which differentiation and growth inhibition of leukaemia cells is induced by NO.