ASS1 and cancer: Hypermethylation of the transcription promoter is a common mechanism responsible for the loss of ASS1 expression in several cancers, and previous data suggests that this is indeed the mechanism behind ASS1 silencing in myofibrosarcomas.14, 23 We confirmed that the low ASS1 expression in SK-LMS-1 cells was also attributable to promoter hypermethylation by exposing the cells to the demethylating agent 5-aza-2′-deoxycytidine (5-aza-dC) for 48 h.