Molecular properties of Ankrd26 affected by mutations linked to leukemia and carcinoma formation

Derailed signaling originating from the plasma membrane is associated with many types of cancer. Different human cancers and thrombocytopenia are linked to ANKRD26 mutations. We unveil that Ankrd26 is a plasma membrane-localized protein forming nanoclusters and that Ankrd26 is critical for retinoic acid/BDNF-induced neuroblastoma differentiation. An N-terminal amphipathic structure lacking in an AML-associated Ankrd26 mutant is indispensable for membrane binding and bending by partial membrane insertion and renders Ankrd26 inactive in both gain-of-function and loss-of- function/rescue studies addressing cellular differentiation. In a papillary thyroid carcinoma-linked mutant, truncated Ankrd26 is fused with the kinase domain of the protooncogene RET. Our data show that the Ankrd26 part of this fusion mutant mediates anchoring of the RET kinase domain to the plasma membrane and self-association by the coiled coil domain of Ankrd26. Ankrd26-RET fusion led to massively increased ERK1/2 activity and RET autophosphorylation at both Y905 and Y1015, i.e. caused aberrant RET signaling. Our results highlight the importance and molecular details of Ankrd26-mediated organizational platforms for cellular differentiation and signaling pathways from the plasma membrane, which, if derailed, lead to cancer-associated pathomechanisms involving the unveiled Ankrd26 properties.