Figure 4.

Hypoxia induces an energy-depleting response in HNSCC cells by activating the AMPK pathway. (A) Western blot analysis of whole cell lysates harvested from serum-deprived HN13 cells grown under normoxic (N) versus hypoxic (H) conditions for 18 hours shows a marked increase in the phosphorylated status of AMPK and its downstream target ACC. In addition, hypoxia-induced energy stress up-regulates REDD1 and affects mTOR activity by preventing S6 phosphorylation. (B) Cellular ATP levels were determined by luminescence in total whole cell lysates derived from HN13 cells cultured under similar conditions as described in (A). The energy-depleting reagent 2-DG (25 mM for 18 hours) was used as a positive control for AMPK activation. Representative data from two independent experiments performed in triplicates and expressed as the mean ± SEM; *P < .01 and **P < .02 versus normoxic conditions, respectively.