Sex differences in the GSK3β-mediated survival of adherent leukemic progenitors

Abstract

Therapeutic resistance of acute myeloid leukemia stem cells, enriched in the CD34 þ 38 À 123 þ progenitor population, is supported by extrinsic factors such as the bone marrow niche. Here, we report that when adherent onto fibronectin or osteoblast components, CD34 þ 38 À 123 þ progenitors survive through an integrin-dependent activation of glycogen synthase kinase 3b (GSK3b) by serine 9-dephosphorylation. Strikingly, GSK3b-mediated survival was restricted to leukemic progenitors from female patients. GSK3b inhibition restored sensitivity to etoposide, and impaired the clonogenic capacities of adherent leukemic progenitors from female patients. In leukemic progenitors from female but not male patients, the scaffolding protein RACK1, activated downstream of a 5 b 1 -integrin engagement, was specifically upregulated and controlled GSK3b activation through the phosphatase protein phosphatase 2A (PP2A). In a mirrored manner, survival of adherent progenitors (CD34 þ 38 À ) from male but not female healthy donors was partially dependent on this pathway. We conclude that the GSK3b-dependent survival pathway might be sex-specific in normal immature population and flip-flopped upon leukemogenesis. Taken together, our results strengthen GSK3b as a promising target for leukemic stem cell therapy and reveal gender differences as a new parameter in anti-leukemia therapy.

Novel Non-phosphorylated Serine 9/21 GSK3β/α Antibodies: Expanding the Tools for Studying GSK3 Regulation

“…Indeed, this regulatory pathway appears to play a role in GSK3β activation under several biological contexts, including cell excitability, survival of leukemic progenitors, insulin signaling, growth factor signaling, and motor protein regulation, among others (Sutherland et al, 1993; Leung-Hagesteijn et al, 2001; Morfini et al, 2004; Lee et al, 2005; Szatmari et al, 2005; Bertrand et al, 2012; Ma et al, 2012). However, protein phosphatases also may influence GSK3β phosphorylation through the Akt pathway (Millward et al, 1999; Bononi et al, 2011).…”

“…S9/S21 phosphorylation leads to inactivation because the N-terminus of GSK3 competitively blocks substrate docking in the primed substrate pocket (Frame et al, 2001) acting as a dominant negative regulator of GSK3 activity, especially against substrates requiring priming. In situ , GSK3 is regulated, at least in part, by phosphorylation at S9 from Akt leading to reduced activity (Gold et al, 2000; Varea et al, 2010; Majewska and Szeliga, 2016) and protein phosphatases that dephosphorylate S9 leading to increased activity under several biological contexts (Sutherland et al, 1993; Leung-Hagesteijn et al, 2001; Morfini et al, 2004; Lee et al, 2005; Szatmari et al, 2005; Bertrand et al, 2012). However, the lack of reagents that specifically detect nonphospho-S9 (npS9) GSK3 has limited our ability to directly study dephosphorylation of this N-terminal serine.…”

PAR2-dependent activation of GSK3β regulates the survival of colon stem/progenitor cells

“…Also, PAR 2 has been shown to promote cell adhesion via ␤ 1 -integrin (37), a putative marker of intestinal stem/progenitor cells (15), and our prior work showed that ␤ 1 -integrin activation induced survival via GSK3␤ in leukemic progenitors (4). In histological sections of crypt bottoms and 3D culture, PAR 2 seems to be mostly present in basolateral position where adherens junctions and GSK3␤ are located (21).…”

“…Also, GSK3␤ regulates the Wnt pathway, a major player in the CRC process, as well as epigenetic changes involved in intestinal wound healing (27,41). In CRC, GSK3␤ is overexpressed and overactivated (60), controlling cell survival and therapeutic response (17,18,36), as we have previously shown in leukemia (4,13,14). However, how GSK3␤ is regulated in intestinal stem/progenitor cells and whether it could participate in PAR-dependent cell survival remains unknown.…”

“…We have previously shown that ␣ 5 ␤ 1 -integrins can trigger GSK3␤ activation in leukemic progenitors through a RACK1-PP2A pathway (4,14). In these conditions, GSK3␤ is activated through serine-9 dephosphorylation either directly by PP2A or secondary to PP2A-induced inhibition of Akt.…”