Hypoxia affects Slc7a5 expression through HIF‐2α in differentiated neuronal cells

Abstract

An imbalance of branched‐chain amino acids (BCAAs) in the brain may result in neuropathological conditions, such as autism spectrum disorders. The L‐type amino acid transporter 1 (LAT1), encoded by the solute carrier transporter 7a5 (Slc7a5) gene, is critical for maintaining normal levels of BCAAs in the brain. However, our understanding of the mechanisms that regulate the expression of LAT1/Slc7a5 in neurons is currently limited. Here, we demonstrate that hypoxic conditions result in upregulated expression of Slc7a5 in differentiated neuronal cells (Neuro2A cells induced to differentiate using all‐trans retinoic acid). Mechanistically, hypoxia‐induced expression of Slc7a5 is markedly reduced by short hairpin RNA (shRNA)‐mediated knockdown of hypoxia‐inducible factor 2α (HIF‐2α), but not by shRNA targeting HIF‐1α, in differentiated neuronal cells. Moreover, hypoxia increased the binding of HIF‐2α to the proximal promoter of Slc7a5 in differentiated neuronal cells. These results indicate that hypoxia directly enhances the recruitment of HIF‐2α to the proximal promoter of Slc7a5, resulting in its upregulated expression in differentiated neuronal cells. These findings indicate that Slc7a5 may be a novel gene responsive to hypoxia in a HIF‐2α‐dependent manner in differentiated neuronal cells.

Putative roles of SLC7A5 (LAT1) transporter in pain

“…Reduced oxygen availability (hypoxia) affects LAT1′s expression through hypoxia-inducible factor 2α (HIF-2α) ( Elorza et al, 2012 , Onishi et al, 2019 ). HIF-2α is a transcriptional factor that promotes adaptation to hypoxic/ischemic stress in response to low tissue oxygenation ( Simon, 2016 ).…”

“…HIF-2α possesses proliferative and tumor promoting properties ( Raval et al, 2005 , Gordan et al, 2007 ). In the differentiated neuroblastoma cells (Neuro2A) exposed to hypoxia, the expression of LAT1 is significantly increased ( Onishi et al, 2019 ). In the same study, when cells were retrovirally infected using short hairpin RNA (shRNA) for HIF-2α, hypoxia-induced upregulation of the expression of LAT1 was completely blocked ( Onishi et al, 2019 ).…”

“…In the differentiated neuroblastoma cells (Neuro2A) exposed to hypoxia, the expression of LAT1 is significantly increased ( Onishi et al, 2019 ). In the same study, when cells were retrovirally infected using short hairpin RNA (shRNA) for HIF-2α, hypoxia-induced upregulation of the expression of LAT1 was completely blocked ( Onishi et al, 2019 ). Surprisingly, hypoxia induces not only LAT1′s expression but also mTORC1′s activation in differentiated neuronal cells ( Onishi et al, 2019 ).…”

“…In the same study, when cells were retrovirally infected using short hairpin RNA (shRNA) for HIF-2α, hypoxia-induced upregulation of the expression of LAT1 was completely blocked ( Onishi et al, 2019 ). Surprisingly, hypoxia induces not only LAT1′s expression but also mTORC1′s activation in differentiated neuronal cells ( Onishi et al, 2019 ). Another study documented that in tumor cells deficient of von Hippel-Lindau (VHL) factor, a component in the E3 ubiquitin ligase complex that marks HIF-2α for degradation, activation of the HIF-2α pathway increases mTORC1′s activity by upregulating the expression of LAT1 ( Elorza et al, 2012 ).…”

Amino Acid Transporters as Potential Therapeutic Targets in Thyroid Cancer

“…Furthermore, hypoxia-inducible factor (HIF) 2 regulates LAT1. HIF2a, an isoform of the HIF family regulating responses to hypoxia, binds to the LAT1 promoter and upregulates LAT1 in renal carcinoma and neuronal cells [87,88]. Exogenous HIF2a upregulation induces LAT1 expression in the lung and liver tissues, wherein LAT1 is generally downregulated [87].…”