TGF-β–FOXO signalling maintains leukaemia-initiating cells in chronic myeloid leukaemia

Abstract

Chronic myeloid leukaemia (CML) is caused by a defined genetic abnormality that generates BCR-ABL, a constitutively active tyrosine kinase 1 . It is widely believed that BCR-ABL activates Akt signalling that suppresses the forkhead O transcription factors (FOXO), supporting the proliferation or inhibiting the apoptosis of CML cells [2][3][4] . Although the use of the tyrosine kinase inhibitor imatinib is a breakthrough for CML therapy, imatinib does not deplete the leukaemiainitiating cells (LICs) that drive the recurrence of CML [5][6][7][8] . Here, using a syngeneic transplantation system and a CML-like myeloproliferative disease mouse model, we show that Foxo3a has an essential role in the maintenance of CML LICs. We find that cells with nuclear localization of Foxo3a and decreased Akt phosphorylation are enriched in the LIC population. Serial transplantation of LICs generated from Foxo3a 1/1 and Foxo3a 2/2 mice shows that the ability of LICs to cause disease is significantly decreased by Foxo3a deficiency. Furthermore, we find that TGF-b is a critical regulator of Akt activation in LICs and controls Foxo3a localization. A combination of TGF-b inhibition, Foxo3a deficiency and imatinib treatment led to efficient depletion of CML in vivo. Furthermore, the treatment of human CML LICs with a TGF-b inhibitor impaired their colonyforming ability in vitro. Our results demonstrate a critical role for the TGF-b-FOXO pathway in the maintenance of LICs, and strengthen our understanding of the mechanisms that specifically maintain CML LICs in vivo.Although tyrosine kinase inhibitor (TKI) therapy of CML patients efficiently induces the death of leukaemia cells [5][6][7][8] , LICs in these patients can survive this therapy. To understand the molecular mechanisms maintaining CML LICs, we characterized LICs in vivo using a mouse model for CML-like myeloproliferative disease (MPD) 9 . Consistent with previous reports 10-13 , we found that a rare c-Kit 1 Lineage 2 (Lin 2 )Sca-1 1 (KLS 1 ) population of CML cells (that is, bearing markers of normal haematopoietic stem cells (HSCs)) induced efficient CML development in recipient mice (Supplementary Fig. 1). In contrast, neither c-Kit 1 Lin 2 Sca-1 2 (KLS 2 ) cells (which correspond to normal progenitors), nor other CML cell populations expressing differentiation markers, induced CML.We and others have shown that Foxo transcription factors, which are important downstream targets of PI3K-Akt signalling, are essential for the maintenance of self-renewal capacity in normal HSCs [14][15][16] . When a growth factor binds to the appropriate receptor, Akt is activated and phosphorylates Foxo proteins, resulting in their nuclear export and subsequent degradation in the cytoplasm. In the absence of growth factor stimulation, Foxo proteins are retained in an active state in the nucleus and induce their transcriptional targets. In CML cell lines, BCR-ABL is thought to activate PI3K-Akt signalling that leads to nuclear export of Foxo factors and suppression of their transcriptional activity...

Transforming growth factor-β decreases the cancer-initiating cell population within diffuse-type gastric carcinoma cells

“…However, contrary to the present findings for diffuse-type gastric carcinomas, TGF-b was reported to maintain the 'stemness' of glioblastoma-initiating cells (Ikushima et al, 2009;Pen˜uelas et al, 2009). TGF-b also maintains the stem-cell-like properties of leukemiainitiating cells in chronic myeloid leukemia through regulation of AKT activation and FOXO3a localization (Naka et al, 2010). TGF-b might thus have different, tissue-dependent regulatory effects on CICs.…”

Differential apoptotic activities of wild-type FOXL2 and the adult-type granulosa cell tumor-associated mutant FOXL2 (C134W)

“…Activation of FOXO3a promotes cytochrome c release and caspase-mediated cell death by induction of TRAIL, BIM and NOXA in neuroblastoma cells (Obexer et al, 2007). FOXO family members, including FOXO3a, are known tumor suppressors implicated in various cancers (Paik et al, 2007;Kornblau et al, 2010;Naka et al, 2010). Therefore, FOXL2 and FOXO3a seem to utilize common and distinctive signaling pathways to control cellular apoptosis.…”

Low‐dose gemcitabine depletes regulatory T cells and improves survival in the orthotopic Panc02 model of pancreatic cancer

“…16 This therapy, however, had no effect on Treg numbers in the tumor (Supporting Information Fig. S2), indicating that other mechanisms may account for the continuous Treg accumulation.…”

“…administered in saline to mice every 2 days at 25 mg/kg per day for 20 days, starting from the 5th day after tumor cell injection as previously described. 16 Tumor Immunology injection. Gem was i.p.…”