On the relationship of YAP and FAK in hMSCs and osteosarcoma cells: Discrimination of FAK modulation by nuclear YAP depletion or YAP silencing.

The HIPPO pathway effector YAP has been shown to be regulated by FAK-signaling. However, the existence of an inverse relationship between YAP and FAK is unknown. Here we demonstrate in hMSCs and in the human osteosarcoma derived cell line Saos that Verteporfin- or RNAi-dependent YAP depletion has opposing influence on FAK. While Verteporfin strikingly reduced cellular FAK protein and phosphorylation, RNAi led to an increase of both molecules and point on a generalizable aspect of the YAP/FAK interrelationship. YAP depletion also caused down-regulation of osteogenic genes in hMSCs, irrespective from the YAP intervention mode. Verteporfin induced topological changes in conjunction with reduced protein levels of β1 integrin, paxillin, and zyxin of focal adhesions (FAs) in hMSCs, suggesting FAK-decrease-related alterations in FAs, which seems to be a FAK-dependent mechanism. On the cell behavioral level, YAP-FAK-interrelation involves proliferation and senescence, as indicated by proliferation inhibition and increase of β-Galactosidase-activity in hMSCs. Our findings, derived from this dual strategy of YAP intervention, reveal a YAP-FAK relationship in conjunction with molecular and cell behavioral consequences. Moreover, they deepen the current scientific knowledge on YAP from a different scientific point of view, since this inverse YAP/FAK-relationship seems to be transferrable to other cell types, including cell entities with pathological background.