Panoply™ Human FCGRT Knockdown Stable Cell Line

Tumor cells rely on high concentrations of amino acids to sustain their growth and proliferation. While increased macropinocytic uptake and lysosomal degradation of albumin, the most abundant serum protein, in Ras-transformed cells can meet these requirements, how most tumor cells expressing wild-type Ras achieve this remains unclear. Here, researchers reveal that the neonatal Fc receptor, FcRn (FCGRT), regulates tumor cell proliferation through recycling of its ligand, albumin. Compared with normal epithelial cells, they found very low or undetectable levels of human FcRn in most tumor cell lines analyzed. Notably, in FcRn-positive tumor cell lines, shRNA-mediated knockdown of FcRn expression led to a significant increase in tumor xenograft growth, whereas forced expression of the receptor via lentiviral transduction had the opposite effect. Furthermore, intracellular albumin and glutamate levels were elevated due to the loss of FcRn-mediated albumin recycling and hypoalbuminemia in tumor-bearing mice. These studies reveal a novel role for FcRn as a tumor growth suppressor and have important implications for the application of this receptor as a prognostic marker and therapeutic target.

To further investigate the behavior of tumor cell lines, the researchers used in vitro assays using albumin as the sole amino acid source to analyze the effects of FcRn expression on glutamate accumulation and proliferation. Under these conditions, glutamate serves as a marker for albumin uptake and lysosomal degradation. FcRn-knockdown HCC1419 cells exhibited elevated intracellular glutamate and proliferation (Figures 1A and 1B). In contrast, DU145 cells expressing WT-FcRn exhibited reduced intracellular glutamate levels and proliferation, a phenotype that could be reversed by expression of H166A-FcRn (Figures 1C and 1D). Importantly, when albumin was replaced with 2 mM glutamine, all HCC1419 and DU145 cell lines displayed similar glutamate levels and similar proliferation rates (Figures 1A-D). Furthermore, the effects of FcRn knockdown in HCC1419 cells were reversed by lentiviral transduction of the shRNA-resistant plasmid Res-FcRn. Thus, consistent with xenograft experiments, FcRn expression in tumor cells reduced glutamate accumulation and proliferation in vitro when albumin was used as the amino acid source.

Figure 1. The expression level of FcRn regulates intracellular glutamate levels and cell proliferation. (Swiercz R, et al., 2016)