Molecular characterization of a human cation‐Cl⁻ cotransporter (SLC12A8A, CCC9A) that promotes polyamine and amino acid transport

Abstract

Cation-Cl- cotransporters (CCCs) belong to a large family of proteins that includes 9 isoforms, two of which have still not been ascribed a transport function (CCC8 and CCC9) while the others are all known to promote Cl(-)-coupled Na+ and/or K+ movement at the cell surface. The CCCs are also included in a larger family termed amino acid-polyamine-organocation carriers (APCs). In contrast to the CCCs, however, polyamine (PA) transporters have thus far been isolated from unicellular species exclusively and do not all belong to the APC family. In this work, we have found that a splice variant of CCC9 (CCC9a) promotes PA-amino acid transport at the surface of HEK-293 cells. We have also found that the influx of PAs in CCC9a-expressing cells is inhibited by pentamidine as well as furosemide, and that it increases further in the presence of specific amino acids but not of Na+, K+, or Cl-. Hence, a group of substrates that are directly transported by CCC9 and the molecular identity of a PA transport system in animal cells may have been uncovered for the first time. These findings are of special interest given that intracellular PAs play a key role in cell proliferation.

Proteome Analysis and Conditional Deletion of the EAAT2 Glutamate Transporter Provide Evidence against a Role of EAAT2 in Pancreatic Insulin Secretion in Mice

“…78), and CCC9A (Slc12a8; Ref. 79) were also not detected. The only one detected was ASCT2 (Slc1a5), which transports glutamate with low affinity (K m ϭ 1.5 mM; Ref.…”

Chloride cotransporters, chloride homeostasis, and synaptic inhibition in the developing auditory system

“…The other branch includes three genes (SLC12A2, SLC12A1, SLC12A3) encoding two bumetanidesensitive Na þ eK þ e2Cl À cotransporters (NKCC1-2) and the thiazide-sensitive Na þ eCl À cotransporter (NCC), respectively (Hebert et al, 2004;Gamba, 2005). Regarding the remaining two members, SLC12A8 (alias CCC9) transports polyamines and amino acids (Daigle et al, 2009), whereas the substrates and the physiological role of SLC12A9 (alias CIP1) are unknown to the present. With the exception of the "kidney-specific" NKCC2 and NCC, all CCC are expressed in neurons and/or glia cells.…”

The Human Carnitine Transporter SLC22A16 Mediates High Affinity Uptake of the Anticancer Polyamine Analogue Bleomycin-A5

“…A very recent report documented that SLC12A8A (CCC9a), a splice variant of the cation/Cl Ϫ cotransporter superfamily, mediates the uptake of polyamines and selected amino acids (e.g. aspartic and glutamic acids) with weak catalytic activity (47). However, SLC12A8A exhibits properties which are markedly at departure with those reported for the ubiquitous polyamine transport system found in mammalian cells (48), and its physiological relevance to polyamine transport remains to be clarified.…”