Abstract
Glucose-mediated signaling regulates the expression of a limited number of genes in human pancreatic β-cells at the transcriptional level. However, it is unclear whether glucose plays a role in posttranscriptional RNA processing or translational control of gene expression. Here, we asked whether glucose affects posttranscriptional steps and regulates protein synthesis in human β-cell lines. We first showed the involvement of the mTOR pathway in glucose-related signaling. We also used the surface sensing of translation technique, based on puromycin incorporation into newly translated proteins, to demonstrate that glucose treatment increased protein translation. Among the list of glucose-induced proteins, we identified the proconvertase PCSK1, an enzyme involved in the proteolytic conversion of proinsulin to insulin, whose translation was induced within minutes following glucose treatment. We finally performed global proteomic analysis by mass spectrometry to characterize newly translated proteins upon glucose treatment. We found enrichment in proteins involved in translation, glycolysis, TCA metabolism, and insulin secretion. Taken together, our study demonstrates that, although glucose minorly affects gene transcription in human β-cells, it plays a major role at the translational level.
Highlights
In insulin-producing pancreatic β-cells, glucose uptake tightly regulates both protein expression levels and cellular function
Activation of the mammalian target of rapamycin pathway is tightly linked to protein translation [21], and its activation is mainly associated to amino acid availability [22]
A parallel increase was observed for the phosphorylation of eukaryotic translation initiation factor 4E-binding protein 1 (4EBP1), another downstream target of mammalian target of rapamycin (mTOR) signaling (Fig. 1, A and C for quantification).The phosphorylation of ribosomal protein S6 (rpS6) and 4EBP1 by glucose was blocked by rapamycin (RAPA), a specific inhibitor of mTORC1 (Fig. 1D and Fig. S1, A and B for quantification)
Summary
In insulin-producing pancreatic β-cells, glucose uptake tightly regulates both protein expression levels and cellular function. We describe and validate the use of the SUnSET approach to demonstrate through FACS and Western blot that glucose increases protein translation in the human cell line EndoC-βH2 [19]. Glucose regulates a very limited number of genes in human β-cells [9], it activates the expression of a large number of proteins (more than 700) involved in the translation machinery, in glucose metabolism and in insulin exocytosis.
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