Hypothyroidism decreases proinsulin gene expression and the attachment of its mRNA and eEF1A protein to the actin cytoskeleton of INS-1E cells

F Goulart-Silva,M.T Nunes,C Serrano-Nascimento

doi:10.1590/s0100-879x2011007500121

F Goulart-Silva, M.T Nunes + Show 1 more

Open Access

https://doi.org/10.1590/s0100-879x2011007500121

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Abstract

The actions of thyroid hormone (TH) on pancreatic beta cells have not been thoroughly explored, with current knowledge being limited to the modulation of insulin secretion in response to glucose, and beta cell viability by regulation of pro-mitotic and pro-apoptotic factors. Therefore, the effects of TH on proinsulin gene expression are not known. This led us to measure: a) proinsulin mRNA expression, b) proinsulin transcripts and eEF1A protein binding to the actin cytoskeleton, c) actin cytoskeleton arrangement, and d) proinsulin mRNA poly(A) tail length modulation in INS-1E cells cultured in different media containing: i) normal fetal bovine serum - FBS (control); ii) normal FBS plus 1 µM or 10 nM T3, for 12 h, and iii) FBS depleted of TH for 24 h (Tx). A decrease in proinsulin mRNA content and attachment to the cytoskeleton were observed in hypothyroid (Tx) beta cells. The amount of eEF1A protein anchored to the cytoskeleton was also reduced in hypothyroidism, and it is worth mentioning that eEF1A is essential to attach transcripts to the cytoskeleton, which might modulate their stability and rate of translation. Proinsulin poly(A) tail length and cytoskeleton arrangement remained unchanged in hypothyroidism. T3 treatment of control cells for 12 h did not induce any changes in the parameters studied. The data indicate that TH is important for proinsulin mRNA expression and translation, since its total amount and attachment to the cytoskeleton are decreased in hypothyroid beta cells, providing evidence that effects of TH on carbohydrate metabolism also include the control of proinsulin gene expression.

Highlights

Thyroid hormone (TH) is known to modulate developmental and metabolic processes by interacting with specific binding sites located in the nucleus, cytoplasm, organelles, and plasma membrane [1,2,3,4,5]
Thyroid hormone did not alter INS-1E cell viability The analysis of membrane integrity of INS-1E cells showed that the absence of TH or T3 treatment did not alter cell viability, since the percentage of control cells (89.62 ± 2.05), hypothyroid (94.57 ± 0.67) or control cells treated with 1 μM T3 (95.96 ± 0.37), or 10 nM T3 (97.82 ± 1.96) with an intact plasma membrane did not change
In the absence of TH, beta cells showed less proinsulin mRNA bound to the actin cytoskeleton; control cells incubated with T3 did not show an alteration of the amount of proinsulin mRNA anchored to the cytoskeleton (Figure 2)

Summary

Introduction

Thyroid hormone (TH) is known to modulate developmental and metabolic processes by interacting with specific binding sites located in the nucleus, cytoplasm, organelles, and plasma membrane [1,2,3,4,5]. TH is known to induce GH gene expression, which might indirectly account for its metabolic effects. The regulation of insulin gene expression is an important step in carbohydrate metabolism, and even though several hormones have been shown to modulate it [15,16,17], the participation of TH in this process has been poorly explored. Recent evidence that TH might post-transcriptionally regulate the expression of certain genes indicates that it can rapidly interfere with the stability and translation rate of distinct mRNAs [18,19].

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