GLS and hepatocellular carcinoma: However, in a doxycycline-regulated Myc transgenic model of HCC, glutamine transporter SLC1A5 is highly expressed, and GLS1/GLS2 is downregulated in both transcripts and protein, which indicates increased extracellular glutamine uptake to anabolic pathway other than fuel source for the TCA cycle (Dolezal et al., 2017).