Figure 3.
Mouse PNET Cell Lines and Tumors Consume and Catabolize Lactate to Establish Metabolic Symbiosis
(A) βTC3 cancer cells cultured in normoxic conditions show low levels of GLUT1 (green) and MCT4 (green) expression, whereas both proteins are upregulated in hypoxic conditions. The scale bars represent 25 μm.
(B) NMR analysis of βTC3 cells, cultured in low glucose (6.25 mM glucose + 2 mM Gln + FCS), plated in the same media at 7 × 106 for 2 days, switched to 0% glucose/0% Gln + FCS ON, then plated in 20 mM 1–13C-glucose + 2 mM Gln +FCS (top) or 20 mM 3–13C-lactate + 2 mM Gln+ FCS, cultured 16 hr in hypoxic (1% O2/5% CO2) or normoxic conditions (20% O2/5% CO2), and harvested for NMR. The net production of lactate in CM from time 0 in 1–13C-glucose conditions in hypoxia was +15.6 mM and normoxia +4.6 mM, while 3–13C-lactate levels were either increased in hypoxia by +0.4 mM or reduced in normoxia by −2.7 mM. The gray arrow highlights 4–13C-glutamine, which was found as a product of 3–13C-lactate catabolism in βTC3 cells when these results were replicated (data not shown).
(C) Tumor-bearing mice were treated for 10 days with Mono-S or R+S, or vehicle control, and then infused with 3–13-C-lactate for 90 min prior to sacrifice. The tumors were excised, quick frozen in liquid nitrogen, and prepared for NMR (see Experimental Procedures).