Glutamine Transporter Expression Profiling Reveal Major Role for ASCT2 and LAT1 in Primary and Metastatic Human Hepatocellular Carcinoma Cells

Abstract

A concerted effort is underway to identify metabolic or physiological derangements in hepatocellular carcinoma (HCC) that may offer targets for therapy. While past work from our lab has documented ASCT2 as the major glutamine transporter in human HCC cells, little is known regarding differences in the array of transporters that operate in primary and metastatic HCC. To address this issue, fourteen human HCC cell lines (7 epithelial and 7 mesenchymal) were evaluated for glutamine transporter expression via reverse‐transcriptase – quantitative polymerase chain reaction (RT‐qPCR) and functional glutamine uptake analyses. The transporters screened via RT‐qPCR were: ASCT2 and LAT1, and six members of the SLC38 glutamine transporter family (System N and A transporters (SNATs)), including SNAT3 and SNAT5 – the dominant System N glutamine transporters in normal hepatocytes. All cell lines universally expressed ASCT2 and LAT1 as well as the SLC38 transporters SNAT2 and SNAT7. The System N transporters SNAT3 and SNAT5 were differentially expressed in some epithelial HCC, while the System A transporters SNAT1 and SNAT4 were variably expressed in both HCC cell types. Functional analysis revealed that the majority of glutamine in all HCC cell lines was transported by a mechanism consistent with ASCT2, independent of transporter mRNA expression signatures. Importantly, ASCT2 and LAT1 transporter activities and cognate mRNA and protein expression levels were discordant, highlighting the complex and layered regulation between gene expression and physiological activity. The results also support continued focus on ASCT2 and LAT1 as a primary therapeutic targets for both primary and metastatic HCC. Support: NIH Grant# R15CA108519 (BPB)