HUMAN COLON-CANCER CELL-LINES SHOW A DIVERSE PATTERN OF NITRIC-OXIDE SYNTHASE GENE-EXPRESSION AND NITRIC-OXIDE GENERATION

A panel of human colonic adenocarcinoma cell lines was examined both f or expression of mRNAs of the nitric oxide synthase (NOS) gene family and for evidence of enzymic activity based on citrulline and nitrite ( NO2-) formation. Reverse transcription-polymerase chain reaction (RT-P CR), revealed that all lines (SW480, SW620, DLD-1 and WiDr) expressed mRNA for the Ca2+-dependent endothelial (e)NOS, while SW480 cells also expressed the Ca2+-dependent neuronal (n)NOS. The mRNA for the Ca2+-i ndependent inducible (i)NOS was expressed both by cytokine-stimulated and by unstimulated SW480, SW620 and DLD-1 cells, but none was seen at any time in the WiDr cells. There was, however, little correlation be tween mRNA expression and enzymic activity based on citrulline and NO2 - formation. Thus none of the cell lines exhibited measurable Ca2+-dep endent NOS activity, while Ca2+-independent NOS activity was seen in a ll but the WiDr cells. Furthermore, DLD-1 cells generated citrulline w ith resultant NO2- formation only after stimulation with lipopolysacch aride (LPS) and/or cytokines, while SW480 and SW620 did so constitutiv ely. Thus RT-PCR studies indicate that tumour cells of similar epithel ial origin display a diverse pattern of NOS gene family expression, an d parallel biochemical studies dearly indicate that such expression do es not always result in measurable enzymic activity leading to the gen eration of NO.