Biomechanical Stimuli Modulate the Expression of Osteolytic Lesion-Related Proteins in an Engineered Human Tumor

Biomechanical forces, either generated by cell contractions or sensed from the microenvironment, have pronounced effects on cell differentiation, growth and survival, playing a key role in the development of many organs. Recent studies have suggested that biomechanical stimuli resulting from tissue stiffening, matrix deformation and interstitial fluid flow regulate pivotal processes in cancer. For instance, increased cytoskeletal tension can arise in response to increased extracellular matrix stiffness, leading to oncogene (Ras)-driven extracellular-signal-regulated kinase (ERK) activation. Notably, RUNX2 transcription factor is regulated by ERK1/2 phosphorylation and is aberrantly expressed at high levels in many cancers invading the bone.

The aim of this study was to investigate the involvement of biomechanical stimuli in the expression of RUNX2 and some of RUNX2 downstream targets associated with osteolytic lesions. To this end, we have developed an in vitro biomimetic 3D human model of Ewing’s Sarcoma (ES) along with a bioreactor platform that allows delivery of biologically relevant mechanical signals.

RUNX2 mRNA and protein were expressed in ES tumors but were down-regulated in ES cell lines cultured in 2D plastic substrates, supporting the importance of the tumor microenvironment. Biomechanical loading of the ES cells within the bioengineered tumor model induced re-expression of RUNX2 and RUNX2 downstream targets OPN, BSP, PTHrP and MMP13. Biomechanical stimuli also induced rapid phosphorylation of ERK1/2, while ERK inhibition completely blocked the expression of OPN and BSP mRNAs. Our findings suggest that biomechanical stimuli are important for the expression of RUNX2 in ES and that they can modulate, upon activation of the ERK signaling cascade, the expression of proteins related to osteolytic disease.