Proton-assisted amino-acid transporters are conserved regulators of proliferation and amino-acid-dependent mTORC1 activation

Abstract

The PI3-kinase (PI3K)/Akt and downstream mammalian target of rapamycin complex 1 (mTORC1) signalling cascades promote normal growth and are frequently hyperactivated in tumour cells. mTORC1 is also regulated by local nutrients, particularly amino acids, but the mechanisms involved are poorly understood. Unexpectedly, members of the proton-assisted amino acid transporter (PAT or SLC36) family emerged from in vivo genetic screens in Drosophila as transporters with uniquely potent effects on mTORC1-mediated growth. Here we show the two human PATs that are widely expressed in normal tissues and cancer cell lines, PAT1 and PAT4, behave similarly to fly PATs when expressed in Drosophila. siRNA knockdown reveals that these molecules are required for activation of mTORC1 targets and for proliferation in human MCF-7 breast cancer and HEK-293 embryonic kidney cell lines. Furthermore, activation of mTORC1 in starved HEK-293 cells stimulated by amino acids requires PAT1 and PAT4, and is elevated in PAT1-overexpressing cells. Importantly, in HEK-293 cells, PAT1 is highly concentrated in intracellular compartments, including endosomes, where mTOR shuttles upon amino acid stimulation. Our data are therefore consistent with a model in which PATs modulate mTORC1's activity not by transporting amino acids into the cell, but by modulating the intracellular response to amino acids.

Metformin directly targets the H3K27me3 demethylase KDM6A/UTX

“…Other transporters included several members of the uptake organic anion transporting polypeptides (OATP) family (SLC21/SLCO) such as SLCO1B1/OATP1B1, SLCO2B1/OATP2B1, and SLCO1B3/OATP1B3, which are known to transport statins, antibiotics, chemotherapeutics, antihistaminic drugs, and diuretics (König, Müller & Fromm, 2013). In addition, the intracellular proton‐assisted amino acid transporter 1 PAT1/SLC36A1, which is an essential component of the amino acid‐sensing engine that drives mTORC1 activation from late endosomes and lysosomes, was included (Heublein et al., 2010). Several zinc‐containing matrix‐degrading endopeptidases (MMP‐1, MMP‐2, MMP‐3), which are known regulators of tissue remodeling in aging and cancer, were also included in the selected list of metformin targets.…”

Effect of high-concentrate diet on amino acid transporter expression and milk quality in Holstein dairy cows

“…A previous study showed that amino acid transporters (AATs) played important roles in the absorption process of AAs and are important nutrient sensing molecules that play an important role in mTOR signaling pathways (Edinger, 2007). A recent study found that only a portion of the AAT was involved in regulating mTOR activation and caused mRNA translation (Heublein et al, 2010). In ruminants, a role of mTOR in the regulation of milk protein synthesis in the mammary glands has also been highlighted (Burgos et al, 2010;Toerien et al, 2010).…”

The Target of Rapamycin: Structure and Functions

“…This transporter could play a role in mTORC1 activation in an amino acid-dependent manner (Heublein et al 2010). Knockdown of PAT1 in MCF-7 cells led to decreased S6K and 4E-BP-1 phosphorylation (Heublein et al 2010). Two membrane transporters, SLC7A5 and SLC3A2, were also shown to be required for mTORC1 activation (Nicklin et al 2009).…”

“…In the lysosomes, the amino acid transporter PAT1 (protonassisted amino acid transporter 1; SLC36A1) is abundant and has been described as a lysosomal amino acid transporter (Russnak et al 2001). This transporter could play a role in mTORC1 activation in an amino acid-dependent manner (Heublein et al 2010). Knockdown of PAT1 in MCF-7 cells led to decreased S6K and 4E-BP-1 phosphorylation (Heublein et al 2010).…”