AKT activation is a feature of CALR mutant myeloproliferative neoplasms

Inhibition of PAK1 generates an ameliorative effect on MPLW515L mouse model of myeloproliferative neoplasms by regulating the differentiation and survival of megakaryocytes

Most thrombopoietin receptor (MPL) mutations result in abnormal megakaryocyte expansion in the spleen or bone marrow (BM), leading to progressive fibrosis. It has been reported that p21 (Rac Family Small GTPase 1 [RAC1])-activated kinase 1 (PAK1) participates in the proliferation and differentiation of megakaryoblasts. PAK1 phosphorylation increased in patients with myeloproliferative neoplasms (MPNs) and murine MPN cells with the Mplw515l mutant gene in this study; however, the function of overactivated PAK1 in MPN cells remains unclear. We found that inhibition of PAK1 caused significant changes in the biological behaviors of MPLW515L mutant cells in vitro, including arrested growth or reduced clonality and increased polyploid DNA and cell apoptosis due to upregulated cleaved caspase 3. In vivo, PAK1 inhibitor treatment caused a slow elevation of leukocytosis and hematocrit (HCT) and a reduction in hepatosplenomegaly in 6133/MPLW515L-transplanted mice, along with reduced tumor cell infiltration and prolonged survival. Further, deletion of PAK1 sustained a relatively normal HCT and platelet count at the beginning of the disease but did not completely alleviate the splenomegaly of MPLW515L mutant mice. Notably, PAK1 knockout attenuated the destruction of splenic structure, and reduced the megakaryocyte burden within the BM. These results suggest that inhibition of PAK1 may be a useful method for treating MPLW515L mutant MPN by intervening megakaryocytes.

The Synergistic Inhibitory Effect of Combining MK-2206 and AZD 6244 in MARIMO Cells Harboring a Calreticulin Gene Mutation

INTRODUCTION

Somatic mutations in the calreticulin (CALR) gene occur in most myeloproliferative neoplasm (MPN) patients who lack Janus kinase 2 or thrombopoietin receptor (MPL) mutations, but the molecular pathogenesis of MPN with mutated CALR is unclear, which limited the further treatment for CALR gene mutant patients.

OBJECTIVES

Previous studies showed that CALR mutations not only activated serine/threonine protein kinase (AKT) in primary mouse bone marrow cells but also mitogen-activated protein kinases (MAPKs) in MARIMO cells harboring a heterozygous 61-bp deletion in CALR exon 9, which were responsible for mutant CALR cell survival, respectively. Hence, we aimed to initially explore the mechanism of AKT activation and observe the synergistic inhibitory effect of combining AKT (MK-2206) and MAPK kinase (AZD 6244) inhibitors in MARIMO cells.

METHODS

We detected the expression of phosphorylated AKT in MARIMO cells treated with inhibitors for 24 or 48 h by western blotting and analyzed cell proliferation, cell cycle, and apoptosis by flow cytometry. We further examined the synergistic inhibitory effect of combining MK-2206 and AZD 6244 in MARIMO cells using the median effect principle of Chou and Talalay.

RESULTS

We found that the AKT was activated in MARIMO cells, and blocking its activity significantly inhibited MARIMO cell growth with downregulation of cyclin D and E, and accelerated cell apoptosis by decreasing Bcl-2 but increasing Bax and cleaved caspase-3 levels in a dose-dependent manner. Further analysis showed that AKT activation was dependent on mammalian target of rapamycin but not on the JAK signaling pathway in MARIMO cells, displaying that inhibition of JAK activity by ruxolitinib (RUX) did not decrease the AKT phosphorylation. Furthermore, the combination of MK-2206 and AZD 6244 produced a significantly synergistic inhibitory effect on MARIMO cells.

CONCLUSIONS

AKT activation is a feature of MARIMO cells and co-targeting of AKT and MAPKs signaling pathways synergistically inhibits MARIMO cell growth.

Activated IL-6 signaling contributes to the pathogenesis of, and is a novel therapeutic target for, CALR-mutated MPNs

Calreticulin (CALR), an endoplasmic reticulum-associated chaperone, is frequently mutated in myeloproliferative neoplasms (MPNs). Mutated CALR promotes downstream JAK2/STAT5 signaling through interaction with, and activation of, the thrombopoietin receptor (MPL). Here, we provide evidence of a novel mechanism contributing to CALR-mutated MPNs, represented by abnormal activation of the interleukin 6 (IL-6)-signaling pathway. We found that UT7 and UT7/mpl cells, engineered by clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) to express the CALR type 1-like (DEL) mutation, acquired cytokine independence and were primed to the megakaryocyte (Mk) lineage. Levels of IL-6 messenger RNA (mRNA), extracellular-released IL-6, membrane-associated glycoprotein 130 (gp130), and IL-6 receptor (IL-6R), phosphorylated JAK1 and STAT3 (p-JAK1 and p-STAT3), and IL-6 promoter region occupancy by STAT3 all resulted in increased CALR DEL cells in the absence of MPL stimulation. Wild-type, but not mutated, CALR physically interacted with gp130 and IL-6R, downregulating their expression on the cell membrane. Agents targeting gp130 (SC-144), IL-6R (tocilizumab [TCZ]), and cell-released IL-6 reduced proliferation of CALR DEL as well as CALR knockout cells, supporting a mutated CALR loss-of-function model. CD34+ cells from CALR-mutated patients showed increased levels of IL-6 mRNA and p-STAT3, and colony-forming unit-Mk growth was inhibited by either SC144 or TCZ, as well as an IL-6 antibody, supporting cell-autonomous activation of the IL-6 pathway. Targeting IL-6 signaling also reduced colony formation by CD34+ cells of JAK2V617F-mutated patients. The combination of TCZ and ruxolitinib was synergistic at very low nanomolar concentrations. Overall, our results suggest that target inhibition of IL-6 signaling may have therapeutic potential in CALR, and possibly JAK2V617F, mutated MPNs.

Cancer Biology of the Endoplasmic Reticulum Lectin Chaperones Calreticulin, Calnexin and PDIA3/ERp57

The lectin chaperones calreticulin (CALR) and calnexin (CANX), together with their co-chaperone PDIA3, are increasingly implicated in studies of human cancers in roles that extend beyond their primary function as quality control facilitators of protein folding within the endoplasmic reticulum (ER). Led by the discovery that cell surface CALR functions as an immunogen that promotes anti-tumour immunity, studies have now expanded to include their potential uses as prognostic markers for cancers, and in regulation of oncogenic signaling that regulate such diverse processes including integrin-dependent cell adhesion and migration, proliferation, cell death and chemotherapeutic resistance. The diversity stems from the increasing recognition that these proteins have an equally diverse spectrum of subcellular and extracellular localization, and which are aberrantly expressed in tumour cells. This review describes key foundational discoveries and highlight recent findings that further our understanding of the plethora of activities mediated by CALR, CANX and PDIA3.