Ankrd26 is a retinoic acid-responsive plasma membrane-binding and -shaping protein critical for proper cell differentiation.

Morphogens are important triggers for differentiation processes. Yet, downstream effectors that organize cell shape changes in response to morphogenic cues, such as retinoic acid, largely remain elusive. Additionally, derailed plasma membrane-derived signaling often is associated with cancer. We identify Ankrd26 as a critical player in cellular differentiation and as plasma membrane-localized protein able to self-associate and form clusters at the plasma membrane in response to retinoic acid. We show that Ankrd26 uses an N-terminal amphipathic structure for membrane binding and bending. Importantly, in an acute myeloid leukemia-associated Ankrd26 mutant, this critical structure was absent, and Ankrd26's membrane association and shaping abilities were impaired. In line with this, the mutation rendered Ankrd26 inactive in both gain-of-function and loss-of-function/rescue studies addressing retinoic acid/brain-derived neurotrophic factor (BDNF)-induced neuroblastoma differentiation. Our results highlight the importance and molecular details of Ankrd26-mediated organizational platforms for cellular differentiation at the plasma membrane and how impairment of these platforms leads to cancer-associated pathomechanisms involving these Ankrd26 properties.

Ankyrin repeat-containing N-Ank proteins shape cellular membranes.

Cells of multicellular organisms need to adopt specific morphologies. However, the molecular mechanisms bringing about membrane topology changes are far from understood-mainly because knowledge of membrane-shaping proteins that can promote local membrane curvatures is still limited. Our analyses unveiled that several members of a large, previously unrecognised protein family, which we termed N-Ank proteins, use a combination of their ankyrin repeat array and an amino (N)-terminal amphipathic helix to bind and shape membranes. Consistently, functional analyses revealed that the N-Ank protein ankycorbin (NORPEG/RAI14), which was exemplarily characterised further, plays an important, ankyrin repeat-based and N-terminal amphipathic helix-dependent role in early morphogenesis of neurons. This function furthermore required coiled coil-mediated self-assembly and manifested as ankycorbin nanodomains marked by protrusive membrane topologies. In summary, here, we unveil a class of powerful membrane shapers and thereby assign mechanistic and cell biological functions to the N-Ank protein superfamily.