ARHGAP21 protein, a new partner of α-tubulin involved in cell-cell adhesion formation and essential for epithelial-mesenchymal transition.

Cell-cell adhesions and the cytoskeletons play important and coordinated roles in cell biology, including cell differentiation, development, and migration. Adhesion and cytoskeletal dynamics are regulated by Rho-GTPases. ARHGAP21 is a negative regulator of Rho-GTPases, particularly Cdc42. Here we assess the function of ARHGAP21 in cell-cell adhesion, cell migration, and scattering. We find that ARHGAP21 is localized in the nucleus, cytoplasm, or perinuclear region but is transiently redistributed to cell-cell junctions 4 h after initiation of cell-cell adhesion. ARHGAP21 interacts with Cdc42, and decreased Cdc42 activity coincides with the appearance of ARHGAP21 at the cell-cell junctions. Cells lacking ARHGAP21 expression show weaker cell-cell adhesions, increased cell migration, and a diminished ability to undergo hepatocyte growth factor-induced epithelial-mesenchymal transition (EMT). In addition, ARHGAP21 interacts with α-tubulin, and it is essential for α-tubulin acetylation in EMT. Our findings indicate that ARHGAP21 is a Rho-GAP involved in cell-cell junction remodeling and that ARHGAP21 affects migration and EMT through α-tubulin interaction and acetylation.

Drug targeting of NR4A nuclear receptors for treatment of acute myeloid leukemia.

NR4As are AML tumor suppressors that are frequently silenced in human acute myeloid leukemia (AML). Despite their potential as novel targets for therapeutic intervention, mechanisms of NR4A silencing and strategies for their reactivation remain poorly defined. Here we show that NR4A silencing in AML occurs through blockade of transcriptional elongation rather than epigenetic promoter silencing. By intersection of NR4A-regulated gene signatures captured upon acute, exogenous expression of NR4As in human AML cells with in silico chemical genomics screening, we identify several FDA-approved drugs including dihydroergotamine (DHE) that reactivate NR4A expression and regulate NR4A-dependent gene signatures. We show that DHE induces NR4A expression via recruitment of the super elongation complex to enable elongation of NR4A promoter paused RNA polymerase II. Finally, DHE exhibits AML selective NR4A-dependent anti-leukemic activity in cytogenetically distinct human AML cells in vitro and delays AML progression in mice revealing its potential as a novel therapeutic agent in AML.