The p70S6K/PI3K/MAPK feedback loop releases the inhibition effect of high-dose rapamycin on rat mesangial cell proliferation

Abstract

Glomerular mesangial cell (MC) proliferation is one of the causative factors of glomerular diseases and one of their prominent pathological features. Rapamycin can inhibit MC proliferation and slow the progression to chronic renal fibrosis. The present study was designed to observe the role of rapamycin in MC proliferation and to explore the mechanism by which rapamycin acts on Akt and MAPK/ERK1/2 pathways in mesangial cells. MTT assay and flow cytometry were used to evaluate the proliferation and the cell cycle phase of glomerular mesangial cells respectively. The mRNA expression level of p70S6K was detected by RT-qPCR. Western blotting was performed to determine p70S6K, PI3K/Akt, and PI3K/MAPK protein expression. We found that rapamycin could reduce mesangial cell proliferation and arrest the cell cycle in the G1 phase, however the inhibition effect of 1000 nmol/L rapamycin was not higher than that in the 100 nmol/L group. The results of western blotting showed that 1000 nmol/L rapamycin more significantly inhibited the phosphorylation of p70S6K than 100 nmol/L, suggesting there should be another signaling pathway that activates the proliferation of MCs. Moreover, our results revealed that 1000 nmol/L rapamycin led to Raf1-MEK1/2-ERK pathway activation through a p70S6K-PI3K-mediated feedback loop in MCs. This study demonstrated that high-dose rapamycin leads to ERK1/2 activation through a p70S6K/PI3K/MAPK feedback loop in rat MCs, thus reducing the inhibitory effect of rapamycin on MC proliferation.

Early host immune responses in a human organoid-derived gallbladder monolayer to Salmonella Typhi strains from patients with acute and chronic infections: a comparative analysis

“…p70S6 kinase is an enzyme that catalyzes the phosphorylation of the S6 protein and is activated by the mTOR signaling pathway (61, 62). Thus, as expected, the relationship between S6 and p44/p42 MAPK transcription factors is complex and may depend on the specific context and multiple mechanisms, including mTORC1-MAPK feedback loops (63,64).…”

The Efficacy of Rapamycin in Spinal Cord Injury: A Systematic Review and Meta-Analysis of preclinical studies

“…Rapamycin inhibits mTOR Complex 1 (mTORC1), a key regulator of cell growth and metabolism (43). mTORC1 normally phosphorylates and activates p70S6 Kinase (p70S6K), which promotes protein synthesis and cell growth (15,44). Akt is a protein kinase that activates mTORC1 by phosphorylating and inhibiting TSC1/TSC2, negative regulators of mTORC1 (45).…”