Background/Purpose:
The four cytoplasmic polyadenylation element binding proteins (CPEB 1 – 4) function as translational regulator for mRNAs thus linking with tumorigenesis and tumor suppression. In our previous study, CPEB1 was found as a tumor-suppressing protein in neuroblastoma cells with significant changes in the expression of certain mRNAs as well as miRNAs. In this study, we focused on the molecular mechanism of how CPEB1 down-regulated oncogene expression and whether miRNA species play a role in such mechanism.
Methods:
Two human neuroblastoma cells, BE(2)-M17 and SH-SY5Y, were used in this study. Control and CPEB1-overexpressing neuroblastoma cells were harvested for RNA extraction. The levels of miRNAs and mRNAs were quantified by real-time RT-PCR. The relative expression was calculated by setting the individual miRNA or mRNA level in control cells as 100% or 1-fold.
Results:
In CPEB1-overexpressing cells, certain oncogenes were found with lower expression then control: MYCN (76.3% in BE(2)-M17 and 39.2% in SH-SY5Y cells), MYC (47.3% in BE(2)-M17and 35.1% in SH-SY5Y cells), and RAS (63.7% in BE(2)-M17 and 70% in SH-SY5Y cells). When examining the corresponding miRNAs targeting these oncogenes, let-7 miRNA family displayed a significant elevation in response to CPEB1 expression. Among let-7 members, let-7a showed a 2.27-fold increase in BE(2)-M17 and 1.77-fold increase in SH-SY5Y cells.
Conclusions:
Up-regulation of miRNA let-7 and concomitant down-regulation of MYCN may contribute to the tumor-suppressing function of CPEB1 in human neuroblastoma cells.