Translational upregulation of folate receptors is mediated by homocysteine via RNA-heterogeneous nuclear ribonucleoprotein E1 interactions
Aśok C. Antony, … , Hiremagalur N. Jayaram, Sally P. Stabler
Aśok C. Antony, … , Hiremagalur N. Jayaram, Sally P. Stabler
Published January 15, 2004
Citation Information: J Clin Invest. 2004;113(2):285-301. https://doi.org/10.1172/JCI11548.
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Translational upregulation of folate receptors is mediated by homocysteine via RNA-heterogeneous nuclear ribonucleoprotein E1 interactions

Abstract

Cellular acquisition of folate is mediated by folate receptors (FRs) in many malignant and normal human cells. Although FRs are upregulated in folate deficiency and downregulated following folate repletion, the mechanistic basis for this relationship is unclear. Previously we demonstrated that interaction of an 18-base cis-element in the 5′-untranslated region of FR mRNA and a cystolic trans-factor (heterogeneous nuclear ribonucleoprotein E1 [hnRNP E1]) is critical for FR synthesis. However, the molecular mechanisms controlling this interaction, especially within the context of FR regulation and folate status, have remained obscure. Human cervical carcinoma cells exhibited progressively increasing upregulation of FRs after shifting of folate-replete cells to low-folate media, without a proportionate rise in FR mRNA or rise in hnRNP E1. Translational FR upregulation was accompanied by a progressive accumulation of the metabolite homocysteine within cultured cells, which stimulated interaction of the FR mRNA cis-element and hnRNP E1 as well as FR biosynthesis in a dose-dependent manner. Abrupt reversal of folate deficiency also led to a rapid parallel reduction in homocysteine and FR biosynthesis to levels observed in folate-replete cells. Collectively, these results suggest that homocysteine is the key modulator of translational upregulation of FRs and establishes the linkage between perturbed folate metabolism and coordinated upregulation of FRs.

Authors

Aśok C. Antony, Ying-Sheng Tang, Rehana A. Khan, Mangatt P. Biju, Xiangli Xiao, Qing-Jun Li, Xin-Lai Sun, Hiremagalur N. Jayaram, Sally P. Stabler

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Gel-shift assays of the interaction of 18-base cis-element from the 5′-U...
Gel-shift assays of the interaction of 18-base cis-element from the 5′-UTR of FR-α mRNA and the 43-kDa hnRNP E1 by homocysteine and other agents. (a and b) [32P]cis-element (10,000 cpm) was allowed to react with 20 μg dialyzed S-100 fraction from HeLa-IU1-HF cells with indicated concentrations of l-methionine, l-cysteine, dl-homocysteine (Hcy) thiolactone, dl-homocysteine, d-homocystine, l-homocystine, β-mercaptoethanol (β-ME), glutathione, or DTT, and RNA-protein complexes were separated by native PAGE followed by autoradiography. Cell extracts were dialyzed in buffer without DTT. β-ME, β-mercaptoethanol.