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Regulation of amino acid/carnitine transporter B0,+ (ATB0,+) in astrocytes by protein kinase C: Independent effects on raft and non-raft subpopulations

Proteins catalysing transport of polar small molecular weight compounds to the cell (transporters) facilitate both, a delivery of necessary compounds for cell functioning, as well as removal of some, very often toxic, metabolites. Our group has been working on amino acid and carnitine transporters in the brain cells, including a transporter of neutral and basic amino acids – B0,, coded in humans by a SLC6A14 gene and being a member of sodium, chloride-dependent family of neurotransmitter transporters. B0, expression has been reported to be up-regulated in malignant cancer cell lines, nothing has been known, however, about its regulation. Besides regulation at transcription level and the change of total protein amount, protein activity can depend on post-translational modifications and its localization within the cell. The paper demonstrates that B0,+ is phosphorylated by protein kinase C – a kinase which is known to be up-regulated in cancer. This phosphorylation was correlated with the increased amount of B0,+ transporter in the plasma membrane and a concomitant augmented transport activity. It has been also observed that B0,+ is partially localized in cholesterol-rich plasma membrane microdomains and interacts with two proteins present in these domains, namely caveolin-1 and flotillin-1. Phosphorylation was observed to decrease the amount of B0,+ in these microdomains, what could result from either transporter internalization or its lateral movement within the plasma membrane. These results indicate that B0,+ can be regulated by post-translational modification and transporter phosphorylation could be responsible for its increased activity in malicious tumors

Date
14 December 2010