Abstract
Targeted therapies are considered to be the future of cancer treatment. However, the mechanism through which intracellular signaling pathways coordinate to modulate oncogenesis remains to be elucidated. In this study, we describe a novel crosstalk among ERK, AKT and Hippo-YAP pathways, with CD44 as an upstream regulator. High cell density leads to activation of ERK and AKT but inactivation of YAP in cancer cells. CD44 modulates cell proliferation and cell cycle but not apoptosis. The expression and activity of cell cycle genes were cooperatively regulated by ERK, AKT and Hippo-YAP signaling pathways through CD44-mediated mechanisms. In addition, CD44 depletion abrogates cancer stem cell properties of tumor initiating cells. Taken together, we described a paradigm where CD44 functions as an upstream regulator sensing the extracellular environment to modulate ERK, AKT and Hippo-YAP pathways which cooperatively control downstream gene expression to modulate cell contact inhibition of proliferation, cell cycle progression and maintenance of tumor initiating cells. Our current study provides valuable information to design targeted therapeutic strategies in cancers.