MicroRNA-146a-5p Limits Elevated TGF-β Signal during Cell Senescence

The level of cellular p16INK4A gradually increased in the serially subcultured keratinocytes with increasing population doubling (PD) levels (Figure 1A). [...]although senescent cells were detected in exponentially proliferating NHOKs at PD 13.6, the percentage of SA-β-gal positive cells was very low; in contrast, the majority of cells at PD 16.9 displayed characteristics of stress-induced senescence, showing SA-β-gal-positive staining and growth arrest (Figure 1B). Furthermore, the protein level of the p65 subunit of nuclear factor kappa B (NF-κB), which transactivates miR-146a-5p,6 was also steadily enhanced and reached a plateau just before cell cycle arrest (Figure 1A). Because TGF-β1 treatment of exponentially proliferating NHOKs significantly inhibited cell proliferation (Figure 1D) and concomitantly promoted apoptosis (Figure 1E), we next determined whether TGF-β1 was involved in stress-induced senescence of primary NHOKs. The level of TGF-β1 protein gradually increased with increasing PD levels and peaked in senescent cells during stress-induced senescence of primary NHOKs (Figure 1F); its expression pattern seemed to be identical to that of miR-146a-5p (Figure 1C). [...]we assessed whether TGF-β1 can regulate the expression of NF-κB and miR-146a-5p in normal human keratinocytes.