Cellular response to glutamine and/or glucose deprivation in in vitro transformed human fibroblasts

Abstract

Neoplastic transformation is characterized by metabolic rewiring to sustain the elevated biosynthetic demands of highly proliferative cancer cells. To obtain the precursors for macromolecule biosynthesis, cancer cells avidly uptake and metabolize glucose and glutamine. Thus, targeting the availability or metabolism of these nutrients is an attractive anticancer therapeutic strategy. To improve our knowledge concerning how cancer cells respond to nutrient withdrawal, the response to glutamine and/or glucose starvation was studied in human in vitro transformed fibroblasts, deeply characterized at the cellular and molecular level. Concomitant starvation of both nutrients led to rapid loss of cellular adhesion (~16 h after starvation), followed by cell death. Deprivation of glucose alone had the same effect, although at a later time (~48 h after starvation), suggesting that glucose plays a key role in enabling cell attachment to the extracellular matrix. Glutamine deprivation did not induce rapid cell death, but caused a prolonged arrest of cellular proliferation; the cells started dying only 96 h after starvation. Before massive cell death occurred, the effects of all the starvation conditions were reversible. Autophagy activation was observed in cells incubated in the absence of glucose for more than 48 h, while autophagy was not detected under the other starvation conditions. Markers of apoptotic cell death, such as caspase 3, caspase 9 and poly(ADP-ribose) polymerase 1 (PARP-1) proteolytic fragments, were not observed under any growth condition. Glucose and/or glutamine deprivation caused very rapid PARP-1 activation, with marked PARP-1 (poly-ADP) ribosylation and protein (poly-ADP) ribosylation. This activation was not due to starvation-induced DNA double-strand breaks, which appeared at the late stages of deprivation, when most cells died. Collectively, these results highlight a broad range of consequences of glucose and glutamine starvation, which may be taken into account when nutrient availability is used as a target for anticancer therapies.