ASB2 targets filamins A and B to proteasomal degradation

Abstract

The ordered series of proliferation and differentiation from hematopoietic progenitor cells is disrupted in leukemia, resulting in arrest of differentiation at immature proliferative stages. Characterizing the molecular basis of hematopoietic differentiation is therefore important for understanding and treating disease. Retinoic acid induces expression of ankyrin repeat-containing protein with a suppressor of cytokine signaling box 2 (ASB2) in acute promyelocytic leukemia cells, and ASB2 expression inhibits growth and promotes commitment, recapitulating an early step critical for differentiation. ASB2 is the specificity subunit of an E3 ubiquitin ligase complex and is proposed to exert its effects by regulating the turnover of specific proteins; however, no ASB2 substrates had been identi-

ASB2α, an E3 Ubiquitin Ligase Specificity Subunit, Regulates Cell Spreading and Triggers Proteasomal Degradation of Filamins by Targeting the Filamin Calponin Homology 1 Domain

“…Western blotting, immunofluorescence, and flow cytometry assays, we previously showed that ASB2␣ expression triggers polyubiquitination and proteasomal degradation of filamins (5)(6)(7)31). In keeping with our earlier studies (7), flow cytometric degradation assays show that the FLNa ABD is both necessary and sufficient for ASB2␣-mediated degradation as the isolated ABD is efficiently degraded following ASB2␣ expression, although FLNa lacking the ABD is resistant to degradation (Fig.…”

“…We have shown that ASB2␣ expression triggers rapid proteasomal degradation of filamins in various cell types (5)(6)(7). Furthermore, retinoic acid-induced expression of ASB2␣ correlates with filamin down-regulation in myeloid leukemia cells induced to differentiate (5), and knock down of endogenous ASB2␣ delays filamin degradation and differentiation (5).…”

“…GST-FLNaABD K42R/K43R/K135R was generated by QuikChange site-directed mutagenesis. dsRed-ASB2␣ and dsRed-ASB2␣⌬S expression constructs were described previously (5,7,31).…”

“…Furthermore, retinoic acid-induced expression of ASB2␣ correlates with filamin down-regulation in myeloid leukemia cells induced to differentiate (5), and knock down of endogenous ASB2␣ delays filamin degradation and differentiation (5). Loss of filamins may therefore play a key role in hematopoietic cell differentiation.…”

Filamin structure, function and mechanics: are altered filamin-mediated force responses associated with human disease?

“…FLNA is a substrate for multiple kinases (reviewed in Sarkisian et al 2008) depending on whether or not its actin bound (Kawamoto and Hidaka 1984), with its cross-linking activity itself regulated by phosphorylation (Cukier et al 2007). FLN is a substrate for the Ca 2+ -activated protease calpain (Gorlin et al 1990) and for the ASB2 ubiquitin ligase (Heuze et al 2008) which provide irreversible regulatory mechanisms for severing FLN cross-links in processes requiring membrane and cytoskeleton remodelling such as cell migration (Marzia et al 2006;Baldassarre et al 2009) and receptor cycling (Seck et al 2003). FLN's role in cell motility and spreading appears to be cell-type dependent.…”