Role of HIF-1α in the hypoxia inducible expression of the thiamine transporter, SLC19A3

Abstract

Ensuring continuous intracellular supply of thiamine is essential to maintain metabolism. Cellular homeostasis requires the function of the membrane bound thiamine transporters THTR1 and THTR2. In the absence of increased dietary intake of thiamine, varying intracellular levels to meet metabolic demands during pathophysiological stressors, such as hypoxia, requires adaptive regulatory mechanisms to increase thiamine transport capacity. Previous work has established the up-regulation of SLC19A3 (THTR2) gene expression and activity during hypoxic stress through the activity of the hypoxia inducible transcription factor 1 alpha (HIF-1α). However, it is unknown whether HIF-1α acts directly or indirectly to trans-activate expression of SLC19A3. This work utilized the breast cancer cell line BT-474 treated with 1% O2 or a hypoxia chemical mimetic deferoxamine to determine the minimal promoter region of SLC19A3 responsible for hypoxia responsiveness. In silico sequence analysis determined two contiguous hypoxia responsive elements in close proximity to the transcriptional start site of the SLC19A3 gene. Using a HIF-1α transcriptional factor ELISA assay, HIF-1α was capable of binding to a dsDNA construct of the SLC19A3 minimal promoter. Chromatin immunoprecipitation assay established that SP1 was bound to the SLC19A3 minimal promoter region under normoxic conditions. However, HIF-1α binding to the minimal promoter region occurred during hypoxic treatments, while no SP1 binding was observed under these conditions. This work demonstrates the direct binding and activation of SLC19A3 expression by HIF-1α during hypoxic stress, suggesting an important adaptive regulatory role for HIF-1α in maintaining thiamine homeostasis.

A guide to plasma membrane solute carrier proteins

“…Expression of SLC19A3 in cancerous cells has been shown to be both increased and decreased and further studies are needed to elucidate the role SLC19A3 plays in cancer cells [224,231]. SLC19A3, like other transporters that have been discussed in the review, is also regulated by HIF-1a [232]. This study showed that under hypoxic conditions the expression of SLC19A3 is induced, leading to higher import of thiamine and suggesting an adaptive role for SLC19A3 in hypoxic environments [232].…”

Thiamine deficiency activates hypoxia inducible factor-1α to facilitate pro-apoptotic responses in mouse primary astrocytes

“…To assess changes in protein expression and localization, primary astrocytes were harvested as whole cell lysates (WCL) or nuclear lysates for Western blot analysis as previously described [ 42 ]. WCL (50μg) and nuclear lysates (25μg) were resolved by electrophoresis on 12% SDS-PAGE gels and transferred to a polyvinylidene difluoride membrane.…”

The adaptive regulation of thiamine pyrophosphokinase-1 facilitates malignant growth during supplemental thiamine conditions

“…HIF-1α also mediates SLC19A3 ′s adaptive up-regulation during hypoxia [ 13 ]. However, the regulatory pathways for the two thiamine homeostasis genes diverge in that TPK1 expression was found to be translationally enhanced, while HIF-1α directly transactivates SLC19A3 gene expression [ 21 ]. Our findings for the inhibitory effects of YC-1 on TPK1 expression may also provide further support for the translational regulation of TPK1 expression.…”

“…We have previously established an increase in the expression of SLC19A2 and TPK1 in breast cancer tissue when compared to normal breast tissue [ 20 ]. Furthermore, HIF-1α directly transactivates the adaptive expression of SLC19A3 and enhances thiamine uptake during hypoxic stress [ 13 , 21 ]. Despite thiamine’s implicit requirement for cellular metabolism within hypoxic tumor microenvironments, how changes in thiamine homeostasis impact malignant progression remain unclear.…”