Arginine biosynthesis and
nitric oxide (NO) production are important for
cancer homeostasis. Degradation of
arginine may be used to inhibit liver
tumors with low
argininosuccinate synthetase (ASS) expression. In this report, we investigated an alternative therapeutic approach by targeting
argininosuccinate lyase (ASL). ASL is transcriptionally induced by endoplasmic reticulum stress and is overexpressed in some human liver
tumors. Knockdown of ASL expression by
short hairpin RNA (
shRNA) in three
liver cancer cell lines, ML-1, HuH-7, and HepG2, decreased colony formation in vitro and
tumor growth in vivo. Furthermore, lentiviral
infection of ASL
shRNA inhibited
tumor growth in a therapeutic animal
tumor model. Analysis of ASL
shRNA on the cell-cycle progression revealed a G2-M delay. Among cell-cycle regulatory molecules,
cyclin A2 expression was reduced. Reintroduction of exogenous
cyclin A2 restored the cell growth in ASL-knockdown cells. Autophagy was observed in the cells treated with ASL
shRNA, as shown by an increase in LC3-II levels and autophagosome formation. The total cellular
arginine level was not altered significantly. Inhibition of autophagy further attenuated cell growth, suggesting that autophagy induced by ASL
shRNA plays a feedback prosurvival function. Knockdown of ASL reduced NO content, and addition of NO donor partially recovered the growth inhibition by ASL
shRNA. In summary, downregulation of ASL attenuated
tumor growth and the inhibition was mainly mediated by a decrease of
cyclin A2 and NO.