Abelson kinases intrinsically disordered linker plays important roles in protein function and protein stability
The non-receptor tyrosine kinase Abelson (Abl) is a key player in oncogenesis, with kinase inhibitors serving as paradigms of targeted therapy. Abl also is a critical regulator of normal development, playing conserved roles in regulating cell behavior, brain development and morphogenesis. Drosophila offers a superb model for studying Abls normal function, because, unlike mammals, there is only a single fly Abl family member. Abl has multiple roles in embryonic morphogenesis, and we and others have begun to take Abl apart as a machine. This revealed many surprises. For instance, kinase activity, while important, is not crucial for all Abl activities, and the C-terminal F-actin binding domain plays a very modest role. This turned our attention to less well-known feature--the long intrinsically-disordered region (IDR) linking Abls kinase and F-actin binding domains. The past decade revealed unexpected, important roles for IDRs in diverse cell functions, by mediating multivalent interactions, enabling assembly of biomolecular condensates via phase separation. Previous work deleting conserved regions revealed an important role for a PXXP motif in the IDR, but did not identify any other essential regions. Here we extend this, deleting the entire IDR. This revealed essential roles for the IDR in embryonic and adult viability, and in cell shape changes and cytoskeletal regulation during embryonic morphogenesis. Strikingly, Abl{Delta}IDR acts as dominant negative, worsening the phenotype of the null mutant. Abl{Delta}IDR accumulates at >10-fold higher levels than wildtype Abl in both Drosophila embryos and cultured cells, suggesting important roles for the IDR in modulating protein stability.