ROR1 activation loop is not phosphorylated upon Wnt5a stimulation of cells.

<p>Quantitative mass spectrometry reveals little or no phosphorylation of the ROR1 activation loop following Wnt5a treatment. Stable isotope labeled synthetic peptides corresponding to the kinase activation loop of ROR1 were used to determine the extent of phosphorylation of ROR1 following Wnt5a treatment of 293 cells. a) Representative chromatograms of isotopically labeled apo-peptide (Blue) and native isolated apo-peptide (Red). b) Representative chromatograms of isotopically labeled phosphopeptides (Blue) and endogenous isolated peptides for each of the three tyrosines in the activation loop (Red). A, Integrated peak area. Dotted lines indicate expected peak times in the native chromatogram. Y-axis scale is reduced in b) to illustrate the limits of detection and quantitation.