Reciprocal Regulation of Abl kinase by CrkII Y251 and Abi1 Controls Cell Motility and Invasion in Glioblastoma

Abstract

The Src homology 2 (SH2) and Src homology 3 (SH3) domain‐containing adaptor protein, Crk II, positively regulates cell motility and in certain tumor types such as Glioblastoma multiformae (GBM) can promote cell invasion and tumor metastasis. Recently, we reported on a novel paradigm by which Crk II regulates motility in breast cancer cells by virtue of its ability to become phosphorylated at tyrosine 251 in the carboxyl‐terminal SH3 domain and activate Abl kinase. Here we show that Tyr251 phosphorylation and Abl activation is a prominent feature in GBM, which in turn promotes both enhanced motility and invasion of tumor cells, and all these events are potentiated by the loss of the SH3 domain containing adaptor protein Abi‐1. At molecular level, both Crk and Abi‐1 compete with their respective SH3 domains for binding the same proline‐rich domain on the Abl kinase, but do so with different intracellular itineraries, where Crk II is a positive regulator and Abi1 is a negative regulator of Abl kinase activity. Moreover, using Abi‐1 (‐/‐) fibroblasts, genetically‐modified GBM cell lines, and in vitro kinase assays, we show that Crk II mediated transactivation of Abl kinase is enhanced by loss of Abi1 in GBM cell lines, and conversely, that re‐expression of Abi‐1 suppresses Crk‐mediated Abl‐transactivation as well as the motility and invasion‐promoting activities of Crk in GBM. Taken together with expression obtained from GBM tumors, these results show that Abi1 and Crk have opposing biological effects on Abl and that CrkII Y251‐Abl kinase regulatory circuit can be unleashed by loss of Abi1 isoform2 in GBM.