Induction of Wnt/β-catenin signaling in mouse mesenchymal stem cells is associated with activation of the p130 and E2f4 and formation of the p130/Gsk3β/β-catenin complex.

Proteins p130 and E2f4, members of the retinoblastoma protein (pRb) family/E2F transcription factor family, are the key elements in regulation of cell cycle and differentiation. The functional role of the p130/E2f4 in mesenchymal stem cells (MSC) is unclear. We demonstrate here that activation of the Wnt/beta-catenin pathway in mouse MSC is associated with accumulation of active forms of the p130, E2f4, and b-catenin but does not result in inhibition of cell cycle progression. The levels and phosphorylation patterns of p130, E2f4, and beta-catenin in MSC do not change during cell cycle progression. This is different from control T98G glyoblastoma cells that accumulated differently phosphorylated forms of the p130 in quiescence, and under active proliferation. In MSC, synchronized at G0/G1 and S cell cycle phases, the p130 and beta-catenin physically interact each other, whereas Gsk3 beta was associated and co-precipitated with both p130 and beta-catenin. Our results indicate that Wnt/b-catenin and pRb signal pathways interact with each other and form common p130/Gsk3 beta/beta-catenin complex during MSC cycle progression. Physiological relevance of such complex may be associated with coupling of the cell cycle and differentiation in MSC, which is related to a wide differentiation potential of these stem cells.