Involvement of miR-190b in Xbp1 mRNA Splicing upon Tocotrienol Treatment

We previously demonstrated that apoptosis induced by tocotrienols (gamma and delta T3) in HeLa cells is preceded by Ca2+ release from the endoplasmic reticulum. This event is eventually followed by the induction of specific calcium-dependent signals, leading to the expression and activation of the gene encoding for the IRE1 alpha protein and, in turn, to the alternative splicing of the pro-apoptotic protein sXbp1 and other molecules involved in the unfolded protein response, the core pathway coping with EndoR stress. Here, we showed that treatment with T3s induces the expression of a specific set of miRNAs in HeLa cells. Data interrogation based on the intersection of this set of miRNAs with a set of genes previously differentially expressed after gamma T3 treatment provided a few miRNA candidates to be the effectors of EndoR-stress-induced apoptosis. To identify the best candidate to act as the effector of the Xbp1-mediated apoptotic response to gamma T3, we performed in silico analysis based on the evaluation of the highest Delta in Gibbs energy of different mRNA-miRNA-Argonaute (AGO) protein complexes. The involvement of the best candidate identified in silico, miR-190b, in Xbp1 splicing was confirmed in vitro using T3-treated cells pre-incubated with the specific miRNA inhibitor, providing a preliminary indication of its role as an effector of EndoR-stress-induced apoptosis.

Automated summary

Research has shown that apoptosis induced by tocotrienols (T3s) in HeLa cells is accompanied by Ca2+ release from the endoplasmic reticulum and the induction of specific calcium-dependent signals, leading to the expression and activation of the IRE1α protein gene. By analyzing the intersection of a set of miRNAs with previously differentially expressed genes after gamma T3 treatment, potential miRNA candidates were identified as effectors of EndoR-stress-induced apoptosis. In silico analysis identified miR-190b as the best candidate for mediating the Xbp1-mediated apoptotic response to gamma T3, and its involvement was confirmed in vitro with T3-treated cells pre-incubated with a specific miRNA inhibitor.