The ROR1 pseudokinase diversifies signaling outputs in MET-addicted cancer cells.

MET is a master gene controlling a genetic program driving proliferation, apoptosis protection and invasion. The ROR1 pseudokinase acts as a MET substrate. However, its contribution to MET signaling and MET-dependent biological outcomes remains to be elucidated. By structure-function analysis of ROR1 mutants, we show that ROR1 encompasses two major substrate regions: one is located in the proline-rich domain and is directly phosphorylated by MET; the other resides in the pseudokinase domain and is phosphorylated through intermediate activation of SRC. Differential phosphorylation of these two regions dictates the execution of specific responses: phosphorylation of the ROR1 proline-rich domain by MET - but not phosphorylation of the pseudokinase domain by SRC - is necessary and sufficient to control MET-driven proliferation and protection from apoptosis. Differently, both the proline-rich and the pseudokinase domains mediate cell invasion. Consistent with the role of ROR1 in specifying the functional consequences of MET-dependent signals, ROR1 silencing leads to selective attenuation of only some of the signal transduction pathways sustained by MET. These data enlighten the so far elusive function(s) of pseudokinases and identify a mechanism of biological diversification, based on substrate specificity of oncogenic kinases.