8 research outputs found
A calcium- and calpain-dependent pathway determines the response to lenalidomide in myelodysplastic syndromes
Despite the high response rates of individuals with myelodysplastic syndrome (MDS) with deletion of chromosome 5q (del(5q)) to treatment with lenalidomide (LEN) and the recent identification of cereblon (CRBN) as the molecular target of LEN, the cellular mechanism by which LEN eliminates MDS clones remains elusive. Here we performed an RNA interference screen to delineate gene regulatory networks that mediate LEN responsiveness in an MDS cell line, MDSL. We identified GPR68, which encodes a G-protein-coupled receptor that has been implicated in calcium metabolism, as the top candidate gene for modulating sensitivity to LEN. LEN induced GPR68 expression via IKAROS family zinc finger 1 (IKZF1), resulting in increased cytosolic calcium levels and activation of a calcium-dependent calpain, CAPN1, which were requisite steps for induction of apoptosis in MDS cells and in acute myeloid leukemia (AML) cells. In contrast, deletion of GPR68 or inhibition of calcium and calpain activation suppressed LEN-induced cytotoxicity. Moreover, expression of calpastatin (CAST), an endogenous CAPN1 inhibitor that is encoded by a gene (CAST) deleted in del(5q) MDS, correlated with LEN responsiveness in patients with del(5q) MDS. Depletion of CAST restored responsiveness of LEN-resistant non-del(5q) MDS cells and AML cells, providing an explanation for the superior responses of patients with del(5q) MDS to LEN treatment. Our study describes a cellular mechanism by which LEN, acting through CRBN and IKZF1, has cytotoxic effects in MDS and AML that depend on a calcium- and calpain-dependent pathway
Cytotoxic effects of bortezomib in myelodysplastic syndrome/acute myeloid leukemia depend on autophagy-mediated lysosomal degradation of TRAF6 and repression of PSMA1
Bortezomib (Velcade) is used widely for
the treatment of various human cancers;
however, its mechanisms of action are
not fully understood, particularly in
myeloid malignancies. Bortezomib is a
selective and reversible inhibitor of the
proteasome. Paradoxically, we find that
bortezomib induces proteasomeindependent
degradation of the TRAF6
protein, but not mRNA, in myelodysplastic
syndrome (MDS) and acute myeloid
leukemia (AML) cell lines and primary
cells. The reduction in TRAF6 protein coincides
with bortezomib-induced autophagy,
and subsequently with apoptosis
in MDS/AML cells. RNAi-mediated
knockdown of TRAF6 sensitized
bortezomib-sensitive and -resistant cell
lines, underscoring the importance of
TRAF6 in bortezomib-induced cytotoxicity.
Bortezomib-resistant cells expressing
an shRNA targeting TRAF6 were
resensitized to the cytotoxic effects of
bortezomib due to down-regulation of the
proteasomal subunit -1 (PSMA1). To determine
the molecular consequences of
loss of TRAF6 in MDS/AML cells, in the
present study, we applied gene-expression
profiling and identified an apoptosis
gene signature. Knockdown of TRAF6 in
MDS/AML cell lines or patient samples
resulted in rapid apoptosis and impaired
malignant hematopoietic stem/progenitor
function. In summary, we describe
herein novel mechanisms by which
TRAF6 is regulated through bortezomib/
autophagy\u2013mediated degradation and by
which it alters MDS/AML sensitivity to
bortezomib by controlling PSMA1 expressio
Inflammation rapidly recruits mammalian GMP and MDP from bone marrow into regional lymphatics.
Innate immune cellular effectors are actively consumed during systemic inflammation, but the systemic traffic and the mechanisms that support their replenishment remain unknown. Here, we demonstrate that acute systemic inflammation induces the emergent activation of a previously unrecognized system of rapid migration of granulocyte-macrophage progenitors and committed macrophage-dendritic progenitors, but not other progenitors or stem cells, from bone marrow (BM) to regional lymphatic capillaries. The progenitor traffic to the systemic lymphatic circulation is mediated by Ccl19/Ccr7 and is NF-κB independent, Traf6/IκB-kinase/SNAP23 activation dependent, and is responsible for the secretion of pre-stored Ccl19 by a subpopulation of CD205 <sup>+</sup> /CD172a <sup>+</sup> conventional dendritic cells type 2 and upregulation of BM myeloid progenitor Ccr7 signaling. Mature myeloid Traf6 signaling is anti-inflammatory and necessary for lymph node myeloid cell development. This report unveils the existence and the mechanistic basis of a very early direct traffic of myeloid progenitors from BM to lymphatics during inflammation
MicroRNA-223 dose levels fine tune proliferation and differentiation in human cord blood progenitors and acute myeloid leukemia
A precise understanding of the role of miR-223 in human hematopoiesis and in the pathogenesis of acute myeloid leukemia (AML) is still lacking. By measuring miR-223 expression in blasts from 115 AML patients, we found significantly higher miR-223 levels in patients with favorable prognosis, whereas patients with low miR-223 expression levels were associated with worse outcome. Furthermore, miR-223 was hierarchically expressed in AML subpopulations, with lower expression in leukemic stem cell-containing fractions. Genetic depletion of miR-223 decreased the leukemia initiating cell (LIC) frequency in a myelomonocytic AML mouse model, but it was not mandatory for rapid-onset AML. To relate these observations to physiologic myeloid differentiation, we knocked down or ectopically expressed miR-223 in cord-blood CD34+ cells using lentiviral vectors. Although miR-223 knockdown delayed myeloerythroid precursor differentiation in vitro, it increased myeloid progenitors in vivo following serial xenotransplantation. Ectopic miR-223 expression increased erythropoiesis, T lymphopoiesis, and early B lymphopoiesis in vivo. These findings broaden the role of miR-223 as a regulator of the expansion/differentiation equilibrium in hematopoietic stem and progenitor cells where its impact is dose- and differentiation-stage-dependent. This also explains the complex yet minor role of miR-223 in AML, a heterogeneous disease with variable degree of myeloid differentiation