Overexpression of hsa-miR-663a reduces expression of PLOD3 encoded LH3 protein and secretion of Collagen IV

In the past decade, microRNAs have been uncovered as key regulators of gene expression at post-transcriptional level by the mean of their ability to interact with complementary regions of transcripts and gain repression of translation or RNA degradation. In the attempt to discover novel miRNA induced by ER stress and identify their target genes we performed a combined analysis by the use of miRNA array and 2D-DIGE/mass-spectrometry approach. Comparative analysis of the microRNA profiles revealed that, in the cells exposed to the ER stress inducer Thapsigargin (TG), twenty-four miRNAs are differentially expressed. Among them, hsa-miR-663a turned out to be the most significant TG induced miR. Interestingly, ontological analysis showed that about 26% of predicted miR-663a target genes are related to secretory pathway functions. To identify, miR-663a target genes we performed proteomic analysis by the combined use of 2D-DIGE and mass spectrometry of cells over-expressing miR-663a revealing that miR-663a could potentially target a number of genes having a function within the secretory pathway. In particular, we show that miR-663a, directly targets PLOD3 mRNA encoding Lysyl hydroxylase 3 (LH3) protein, a multifunctional collagen-modifying enzyme. In miR-663a over expressing cells, miR-663a reduces LH3 expression. Reduction of the galactosylhydroxylysine-glucosyltransferase (GGT) activity of LH3 disrupts the localization of type IV collagen, which showed retention in the Endoplasmic Reticulum. Our results suggest that miR-663a could modulate collagen secretion in pathophysiological conditions.