<p>Receptor tyrosine kinase phosphorylation was determined by a commercial kit (Proteome Profiler Human Phospho-RTK Array Kit, R&D Systems, Abingdon, UK) with subsequent densitometric analysis using ImageJ software (<a href="http://imagej.nih.gov/ij/" target="_blank">http://imagej.nih.gov/ij/</a>). A) Receptor tyrosine kinase phosphorylation status expressed as fold change spot density relative to a control membrane area. Images of the membranes are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0172140#pone.0172140.s001" target="_blank">S1 Fig</a>. B) Differential phosphorylation of receptor tyrosine kinases that were found phosphorylated in at least one cell line (as indicated by a fold change spot dens...