Abundant expression of fibronectin is a major feature of leukemic dendritic cells differentiated from patients with acute myeloid leukemia

Isolation of lymph shows dysregulation of STAT3 and CREB pathways in the spleen and liver during leukemia development in a rat model

BACKGROUND AND AIMS

Acute myeloid leukemia (AML) is a heterogeneous malignant condition characterized by massive infiltration of poorly differentiated white blood cells in the blood stream, bone marrow, and extramedullary sites. During leukemic development, hepatosplenomegaly is expected to occur because large blood volumes are continuously filtered through these organs. We asked whether infiltration of leukemic blasts initiated a response that could be detected in the interstitial fluid phase of the spleen and liver.

MATERIAL AND METHODS

We used a rat model known to mimic human AML in growth characteristics and behavior. By cannulating efferent lymphatic vessels from the spleen and liver, we were able to monitor the response of the microenvironment during AML development.

RESULTS AND DISCUSSION

Flow cytometric analysis of lymphocytes showed increased STAT3 and CREB signaling in spleen and depressed signaling in liver, and proteins related to these pathways were identified with a different profile in lymph and plasma in AML compared with control. Additionally, several proteins were differently regulated in the microenvironment of spleen and liver in AML when compared with control.

CONCLUSION

Interstitial fluid, and its surrogate efferent lymph, can be used to provide unique information about responses in AML-infiltered organs and substances released to the general circulation during leukemia development.

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

Therapeutic resistance of acute myeloid leukemia stem cells, enriched in the CD34(+)38(-)123(+) 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(+)38(-)123(+) progenitors survive through an integrin-dependent activation of glycogen synthase kinase 3β (GSK3β) by serine 9-dephosphorylation. Strikingly, GSK3β-mediated survival was restricted to leukemic progenitors from female patients. GSK3β 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 α(5)β(1)-integrin engagement, was specifically upregulated and controlled GSK3β activation through the phosphatase protein phosphatase 2A (PP2A). In a mirrored manner, survival of adherent progenitors (CD34(+)38(-)) from male but not female healthy donors was partially dependent on this pathway. We conclude that the GSK3β-dependent survival pathway might be sex-specific in normal immature population and flip-flopped upon leukemogenesis. Taken together, our results strengthen GSK3β as a promising target for leukemic stem cell therapy and reveal gender differences as a new parameter in anti-leukemia therapy.

Proinflammatory response of human leukemic cells to dsRNA transfection linked to activation of dendritic cells

Leukemic cells exert immunosuppressive effects that interfere with dendritic cell (DC) function and hamper effective antileukemic immune responses. Here, we sought to enhance the immunogenicity of leukemic cells by loading them with the double-stranded (ds) RNA Toll-like receptor 3 (TLR3) ligand polyriboinosinic polyribocytidylic acid (poly(I:C)), mimicking viral infection of the tumor cells. Given the responsiveness of DC to TLR ligands, we hypothesized that the uptake of poly(I:C)-loaded leukemic cells by immature DC (iDC) would lead to DC activation. Primary acute myeloid leukemia (AML) cells and AML cell lines markedly responded to poly(I:C) electroporation by apoptosis, upregulation of TLR3 expression, enhanced expression of major histocompatibility complex (MHC) and costimulatory molecules and by production of type I interferons (IFN). Upon phagocytosis of poly(I:C)-electroporated AML cells, DC maturation and activation were induced as judged by an increased expression of MHC and costimulatory molecules, production of proinflammatory cytokines and an increase of T helper 1 (T(H)1)-polarizing capacity. These immune effects were suboptimal when AML cells were passively pulsed with poly(I:C), indicating the superiority of poly(I:C) transfection over pulsing. Our results demonstrate that poly(I:C) electroporation is a promising strategy to increase the immunogenicity of AML cells and to convert iDC into activated mature DC following the phagocytosis of AML cells.

Expression of novel markers of pancreatic ductal adenocarcinoma in pancreatic nonductal neoplasms: additional evidence of different genetic pathways

Solid pseudopapillary tumor, pancreatoblastoma, undifferentiated carcinoma with osteoclastic-like giant cells, and acinar cell carcinomas are rare pancreatic nonductal neoplasms. Compared to the significant advances in our understanding of the pathogenesis of pancreatic ductal adenocarcinomas in the last decades, the molecular mechanisms underlying pancreatic nonductal neoplasms are poorly understood. In order to elucidate their molecular pathogenesis, we constructed tissue microarrays to study the expression of some novel pancreatic ductal adenocarcinoma-associated tumor markers in these nonductal pancreatic neoplasms. We analyzed nine markers including tumor suppressor gene (14-3-3 sigma), proliferation marker (topoisomerase II alpha), epithelial markers (prostate stem cell antigen, mesothelin and cytokeratin 19), stromal markers (fascin, hsp47 and fibronectin), and gamma-synuclein whose function is not delineated. In addition, we included tumor suppressor gene DPC4 and oncogene Beta-catenin to further confirm their expression in pancreatic nonductal tumors. Our results showed that in contrast to pancreatic ductal adenocarcinomas that show loss of Dpc4 protein in 55% of cases, loss of Dpc4 expression is absent in pancreatic nonductal neoplasms. Expression of 14-3-3 sigma is frequently seen in both pancreatic nonductal neoplasms (25-100%) and ductal adenocarcinomas (89%). Aberrant nuclear expression of beta-catenin is common in pancreatic nonductal neoplasms, specifically in solid pseudopapillary tumors (88%) and pancreatoblastomas (100%) but is rarely seen in pancreatic ductal adenocarcinomas (<5%). Expression of topoisomerase II alpha is not seen in solid pseudopapillary tumors and undifferentiated carcinomas with osteoclastic-like giant cells but is focally seen in pancreatoblastomas (50%) and acinar cell carcinomas (85%). Expression of PSCA and mesothelin was observed in pancreatic nonductal neoplasms but their expression was seen less frequently (0-50%) and weaker than that in pancreatic ductal adenocarcinomas (60-100%). CK19, a marker of pancreatic ductal adenocarcinomas, is not expressed in pancreatic nonductal neoplasms. Expression of gamma-synuclein as well as stromal markers (fascin, hsp47 and fibronectin) is frequently seen in both. Our findings indicate pancreatic nonductal neoplasms have distinctive patterns of protein expression relative to pancreatic ductal adenocarcinomas and suggest that pancreatic nonductal neoplasms have different genetic pathways from the more common pancreatic ductal adenocarcinomas.