Chelsea Briot1*, Natasha Freidman1*, Renae Ryan1
*Authors contributed equally to this work.
The Solute Carrier 1A (SLC1A) family comprises a group of membrane proteins that act as dual-function amino acid transporters and chloride channels (Freidman et al., 2020). It includes the alanine serine cysteine transporters (ASCTs) and the human glutamate transporters known as excitatory amino acid transporters (EAATs). ASCT2 can transport a range of neutral amino acids into cells including glutamine (Utsunomiya-Tate et al., 1996). It is upregulated in a range of solid tumours and is regarded as a promising target for cancer therapy (Liu et al., 2018). L-γ-glutamyl-p-nitroanilide (GPNA) is a compound widely used in studies probing the role of ASCT2 in cancer biology (Trilla-Fuertes et al., 2020; van Geldermalsen et al., 2018; Marshall et al., 2017; Hassanein et al., 2015; Ren et al., 2015). Here, we demonstrate that GPNA activates the chloride conductance of ASCT2 to the same extent as a transported substrate, whilst not undergoing the full transport cycle. This is a previously unreported phenomenon for compounds in the SLC1A family and corroborates a body of literature suggesting that the structural requirements for transport are distinct from those for chloride channel formation (Chen et al., 2021). We also show that in addition to its currently known targets, GPNA inhibits several of the glutamate transporters (EAATs). Together, these findings raise questions surrounding the true mechanisms of its anticancer effects.
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