Identification of novel interactions between the proline- rich motif on Receptor Tyrosine Kinases and the SH3 domain of cytoplasmic proteins under non-stimulated conditions

A “second tier” regulation of signalling from Receptor Tyrosine Kinases (RTK) has been uncovered where the receptor can be activated without ligand stimulation. This is mediated from an interaction between SH3 domains and proline-rich motifs in the RTK C-terminal tail. Most RTKs have one or more proline-rich motifs in their C-terminal tail. The outstanding question remains as to what is the importance of these interactions. Several high-throughput screens have been carried out to discover novel interactions between proline-rich motifs and SH3 domains. One potential candidate is the oncogenic LIM and SH3 domain protein 1 (LASP1). Work presented here demonstrates that LASP1 directly interacts with the C-terminal tail of several RTKs. The oncogenic RTK ErbB2 has been shown to directly interact with LASP1 via the ErbB2 C-terminal tail. More importantly an endogenous interaction was demonstrated in the breast cancer cell line SkBr3. Both LASP1 and ErbB2 are found in the vicinity of each other on the chromosome, and co-overexpression of both proteins has been shown in breast cancers. LASP1 has also been shown to directly interact with Fibroblast Growth Factor Receptor 2 (FGFR2). This interaction happens via the C-terminal tail of FGFR2, which has previously been shown to be important in “second tier” signalling and regulation. Preliminary data suggests that the LASP1 and FGFR2 interaction may impact cell growth and migration. In another example of a “second tier” interaction, the SH3 domains from SRC family kinases FYN and SRC are shown to interact with ErbB2 under starved conditions, and the interaction between SRC and ErbB2 is mediated by a proline-rich motif in ErbB2. Taken together these data demonstrate a role for the C-terminal tail of several RTKs in interacting with proteins in a non-stimulated background, and challenges the canonical view of RTK signalling