A leucine-rich diet modulates the tumour-induced down regulation of the MAPK/ERK and PI3K/Akt/mTOR signalling pathways and maintains the expression of the ubiquitin-proteasome pathway in the placental tissue of NMRI mice

Abstract

Placental tissue injury is concomitant with tumour development. We investigated tumour-driven placental damage by tracing certain steps of the protein synthesis and degradation pathways under leucine-rich diet supplementation in MAC16-tumour-bearing mice. The cell signalling and ubiquitin proteasome pathways were assessed in the placental tissues of pregnant mice distributed into six groups (three groups on control diet: C- pregnant control, MAC- tumour-bearing pregnant, A- pregnant injected with MAC-ascitic fluid; three other groups on a leucine-rich diet: L- pregnant, LMAC- tumour-bearing pregnant, LA- pregnant injected with MAC-ascitic fluid). The MAC tumour growth down-regulated the cell signalling pathways of the placental tissue and decreased the levels of IRS-1, Akt/PKB, Erk/MAPK, mTOR, p70S6K, STAT3, and STAT6 phosphorylated proteins (multiplex Millipore-Luminex assay). Leucine supplementation maintained the levels of these proteins within the established cell signalling pathways. Increased expression of the PC5 gene (qRT-PCR assay) and of the 19S and 20S proteins (Western Blotting) was associated with decreased placental tyrosine only in the W group, reflecting an up-regulated ubiquitin-proteasome pathway. Similar effects were found in the A group, confirming that the tumours' effects were mimicked by MAC-ascitic fluid injection. Although increased protein expression levels were related to degradation pathways in leucine-supplemented conditions, the tumour progressions of all mice were modulated by the leucine-rich diet. Thus, tumour evolution reduced the protein expression of the cell signalling pathway associated with the elevated degradation pathway. However, when tumour-bearing animals were fed a leucine-rich diet, the expressions of cell signalling proteins and the proteolytic pathway were maintained in the placenta. (AU)