ATF4 and liver cancer: To understand the response of liver cancer cells to nutrient deprivation, we propose 3 hypotheses for the AhR-regulated pathway that induces VEGF in glucose-deprived HepG2 cells: A) Nrf2 induces VEGF expression by activating ATF4 expression; B) protein interactions between Nrf2 and ATF4 induce VEGF expression; and C) ATF4 activates VEGF expression independent of Nrf2 (Figure 4).