Merlin relation to cell structure and adhesion in Na,K-ATPase β2 deficient cerebellar neuron progenitors
Date
2019
Authors
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Publisher
University of Delaware
Abstract
The Na,K-ATPase is an ion pump that contains a catalytic α subunit, a glycosylated β subunit, and an auxiliary γ subunit. The β subunits are necessary for sorting the Na,K-ATPase to the cell membrane and are involved in cell adhesion. Out of the three β isoforms (β1, β2 or AMOG, β3), β1 and β2 are expressed in cerebellar granule cells, but their differences in glycosylation and low sequence identity suggests isoform-specific functions. In medulloblastoma cells, knockdown of β2 has a greater effect on Na,K-ATPase pump activity and in cerebellar granule cell progenitors, β2 expression is less affected by Sonic Hedgehog signaling activation than β1 expression. β2 knockdown cells have a more rounded morphology and prolonged Epidermal Growth Factor Receptor (EGFR) activation. These findings may be related to the concurrent increase in Merlin, a linker protein that connects membrane proteins to the cytoskeleton that is associated with EGFR internalization, focal adhesions, and cell junctions. To further investigate Merlin’s neuronal function and interactions in the absence of β2, the localization and expression of focal adhesion proteins and actin were assessed in DAOY cells and cerebellar tissue. Merlin was mostly cytoplasmic but intermittently overlapped with EGFR, focal adhesion proteins vinculin and paxillin at the membrane of β2 knockdown cells. EGFR was internalized when cells were treated with EGF, with differences in endosomal localization in β2 knockdown cells. Protein expression of focal adhesion proteins in β2 knockout (AMOG-/-) cerebellar tissue was similar to wild-type postnatally, while Merlin expression increases in AMOG-/- cerebellum.