In the absence of apoptosis, myeloid cells arrest when deprived of growth factor, but remain viable without ATG5-dependent autophagy or uptake of glucose or glutamine.

Withdrawal of the growth factor interleukin 3 from IL3-dependent myeloid cells causes them to undergo Bax/Bak1-dependent apoptosis, whereas factor-deprived Bax-/-Bak1-/- cells remain viable, but arrest. It was previously reported that withdrawal of IL3 from Bax-/-Bak1-/- cells caused decreased expression of the glucose transporter Glut1, leading to reduced glucose uptake, so that arrested cells required Atg5-dependent autophagy for long-term survival. In other cell types, a decrease in Glut1 is mediated by thioredoxin-interacting protein Txnip, which is induced in IL3-dependent myeloid cells when growth factor is removed. We mutated Atg5 and Txnip by CRISPR/Cas9 and found that Atg5-dependent autophagy was not necessary for the long-term viability of cycling or arrested Bax-/-Bak1-/- cells, and that Txnip was not required for the decrease in Glut1 expression in response to withdrawal of growth factor. Surprisingly, in glucose-free medium, wild-type and Bax/Bak1 double mutant cells not only survived, but continued to cycle when IL3 was present. In contrast, Bax+/+Bak1+/+ cells died by apoptosis when deprived of glutamine, and while Bax-/-Bak1-/- cells deprived of glutamine survived, they arrested even when IL3 was present. Thus, glutamine, but neither Atg5-dependent autophagy nor glucose uptake, is necessary for cell division, and none are needed for arrested Bax-/-Bak1-/- myeloid cells to survive for several weeks.