A Functional Interaction Between Na,K-ATPase β₂-Subunit/AMOG and NF2/Merlin Regulates Growth Factor Signaling in Cerebellar Granule Cells.

The Na,K-ATPase, consisting of a catalytic α-subunit and a regulatory β-subunit, is a ubiquitously expressed ion pump that carries out the transport of Na⁺ and K⁺ across the plasma membranes of most animal cells. In addition to its pump function, Na,K-ATPase serves as a signaling scaffold and a cell adhesion molecule. Of the three β-subunit isoforms, β₁ is found in almost all tissues, while β₂ expression is mostly restricted to brain and muscle. In cerebellar granule cells, the β₂-subunit, also known as adhesion molecule on glia (AMOG), has been linked to neuron-astrocyte adhesion and granule cell migration, suggesting its role in cerebellar development. Nevertheless, little is known about molecular pathways that link the β₂-subunit to its cellular functions. Using cerebellar granule precursor cells, we found that the β₂-subunit, but not the β₁-subunit, negatively regulates the expression of a key activator of the Hippo/YAP signaling pathway, Merlin/neurofibromin-2 (NF2). The knockdown of the β₂-subunit resulted in increased Merlin/NF2 expression and affected downstream targets of Hippo signaling, i.e., increased YAP phosphorylation and decreased expression of N-Ras. Further, the β₂-subunit knockdown altered the kinetics of epidermal growth factor receptor (EGFR) signaling in a Merlin-dependent mode and impaired EGF-induced reorganization of the actin cytoskeleton. Therefore, our studies for the first time provide a functional link between the Na,K-ATPase β₂-subunit and Merlin/NF2 and suggest a role for the β₂-subunit in regulating cytoskeletal dynamics and Hippo/YAP signaling during neuronal differentiation.

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