Insulin-like growth factor-1 prevents miR-122 production in neighbouring cells to curtail its intercellular transfer to ensure proliferation of human hepatoma cells.
Bottom Line: Exosomal miR-122, expressed and released by Huh7 cells and taken by miR-122 deficient HepG2 cells, was found to be effective in repression of target mRNAs and to reduce growth and proliferation of recipient HepG2 cells.Interestingly, in a reciprocal process, HepG2 secretes Insulin-like Growth Factor 1 (IGF1) that decreases miR-122 expression in Huh7 cells.This interaction is mediated via intercellular exosome-mediated miR-122 transfer and countered by a reciprocal IGF1-dependent anti-miR-122 signal.
Affiliation: RNA Biology Research Laboratory, Molecular and Human Genetics Division, CSIR-Indian Institute of Chemical Biology, Kolkata 700032, India.Show MeSH
Related in: MedlinePlus
Mentions: Huh7 is a hepatoma cell that exhibits constitutive expression of miR-122 which is associated with low Cyclin G1 expression level in hepatic cells (29,38,39). Previous experiments indicated that in the presence of HepG2, growth rate of Huh7 increases (Figure 2A). Does HepG2 reduce miR-122 in neighbouring Huh7 cells to increase their proliferation? To investigate this further, Huh7 cells expressing miR-122 reporter were co-cultured either with non-transfected control Huh7 cells or HepG2 cells at a ratio of 1:1. In the presence of HepG2, there was a decrease in the relative fold repression of miR-122 reporter in Huh7 cells as compared to control (Figure 3A and B). Quantitative PCR indicated that there was a decrease in the miR-122 level in HepG2 co-cultured, as opposed to the control Huh7 cells (Figure 3C). This tells us that the observed decrease in miR-122 activity is because of a reduced miR-122 level in Huh7 cells co-cultured with HepG2. Real-time quantification further revealed a similar change in the precursor form of miR-122 (pre-miR-122) in HepG2 exposed Huh7 cells, suggesting a reduced production of miR-122 (Figure 3D). This decrease in transcription appears to be specific for the miR-122 promoter and does not depend on miR-122 identity. When Huh7 cells were transfected with plasmids expressing pre-miR-122 under a U6 promoter (31), there was no change in the miR-122 level in control and HepG2 co-cultured Huh7 cells (Figure 3E). Therefore, it may be concluded that HepG2 cells exert a reciprocal effect on the miR-122 level in co-cultured Huh7 cells primarily by reducing the production of pre-miR-122.
Affiliation: RNA Biology Research Laboratory, Molecular and Human Genetics Division, CSIR-Indian Institute of Chemical Biology, Kolkata 700032, India.