Mechanism of hypercalcemia in adult T-cell leukemia: overexpression of receptor activator of nuclear factor kappaB ligand on adult T-cell leukemia cells

HTLV-1 infected T cells cause bone loss via small extracellular vesicles

Adult T cell leukemia (ATL), caused by infection with human T cell leukemia virus type 1 (HTLV-1), is often complicated by hypercalcemia and osteolytic lesions. Therefore, we studied the communication between patient-derived ATL cells (ATL-PDX) and HTLV-1 immortalized CD4+ T cell lines (HTLV/T) with osteoclasts and their effects on bone mass in mice. Intratibial inoculation of some HTLV/T lead to a profound local decrease in bone mass similar to marrow-replacing ATL-PDX, despite the fact that few HTLV/T cells persisted in the bone. To study the direct effect of HTLV/T and ATL-PDX on osteoclasts, supernatants were added to murine and human osteoclast precursors. ATL-PDX supernatants from hypercalcemic patients promoted formation of mature osteoclasts, while those from HTLV/T were variably stimulatory, but had largely consistent effects between human and murine cultures. Interestingly, this osteoclastic activity did not correlate with expression of osteoclastogenic cytokine RANKL, suggesting an alternative mechanism. HTLV/T and ATL-PDX produce small extracellular vesicles (sEV), known to facilitate HTLV-1 infection. We hypothesized that these sEV also mediate bone loss by targeting osteoclasts. We isolated sEV from both HTLV/T and ATL-PDX, and found they carried most of the activity found in supernatants. In contrast, sEV from uninfected activated T cells had little effect. Analysis of sEV (both active and inactive) by mass spectrometry and electron microscopy confirmed absence of RANKL and intact virus. Viral proteins Tax and Env were only present in sEV from the active, osteoclast-stimulatory group, along with increased representation of proteins involved in osteoclastogenesis and bone resorption. sEV injected over mouse calvaria in the presence of low dose RANKL caused more osteolysis than RANKL alone. Thus, HTLV-1 infection of T cells can cause release of sEV with strong osteolytic potential, providing a mechanism beyond RANKL production that modifies the bone microenvironment, even in the absence of overt leukemia.

Human T-cell Lymphotropic Virus Type 1 (HTLV-1)-Associated Adult T-cell Leukemia/Lymphoma in a Patient Previously Treated for Strongyloidiasis

Adult T-cell leukemia/lymphoma (ATLL) is a rare form of T-cell lymphoma with poor median survival time and limited response to chemotherapy. We present a 45-year-old female from Ghana with generalized body rash, hypercalcemia, lymphadenopathy, and lytic bone lesions. She had a history of strongyloidiasis, treated two years ago, and her serology was positive for the human T-cell lymphotropic virus type 1 (HTLV-1). Histopathology of cervical lymph node and abdominal rash biopsy revealed T-cell lymphoma. We present a literature review on the topic and the challenges of diagnosis. We emphasize the importance of considering HTLV-1-associated ATLL in patients who have been treated for strongyloidiasis in the past and are presenting with rash or lymphadenopathy.

Hypercalcemia in the setting of HTLV-1 infection and a normal PTHrP level

Summary

Human T-cell lymphotropic virus-1 (HTLV-1) causes adult T-cell leukemia and lymphoma (ATLL) and is a rare but important cause of hypercalcemia. A 53-year-old male with HTLV-1-associated myelopathy presented with acute on chronic bilateral lower extremity weakness and numbness. Initial blood work revealed hypercalcemia with corrected calcium of 16.2 mg/dL (8.5-11.5) with normal levels of phosphorus and alkaline phosphatase. Workup for hypercalcemia revealed parathyroid hormone (PTH) of 14 pg/mL (10-65), 25 hydroxy vitamin D at 19.6 ng/mL (30-100), 1,25 dihydroxy vitamin D at 6.7 pg/mL (19.9-79.3), thyroid-stimulating hormone of 1.265 μIU/mL (0.5-5), undetectable PTH-related protein (PTHrP) and lactate dehydrogenase of 433 U/L (100-220). The urine calcium creatinine ratio was 0.388. Reverse transcriptase PCR was positive for HTLV-1 and negative for HTLV-2. Peripheral blood flow cytometry and lymph node biopsy confirmed ATLL. He received treatment with fluids, calcitonin and denosumab after which serum calcium levels fell (nadir: 7.7 mg/dL) and then normalized. Humoral hypercalcemia in this setting is mediated by receptor activator of nuclear factor-kappa B ligand (RANKL), PTHrP and other cytokines. PTHrP levels depend on levels of the TAX gene product, cell type and lymphocyte-specific factors. Thus, a low level, like in our patient, does not rule out HTLV-1 infection/ATLL as the cause of hypercalcemia. Hypercalcemia is known to be responsive to monoclonal antibodies against RANKL given the compound's role in mediating hypercalcemia in these cases.

Learning points

Human T-cell lymphotropic virus-1 infection and adult T-cell leukemia and lymphoma are associated with high rates of hypercalcemia and hypercalcemic crises. Hypercalcemia in these cases is mediated by osteoclastic bone resorption carried out by several agents including receptor activator of nuclear factor-kappa B ligand, parathyroid hormone-related protein (PTHrP), macrophage inflammatory protein 1 alpha, interleukins, etc. A normal PTHRrP does not rule out humoral hypercalcemia of malignancy in this setting, as indicated by this case. Hypercalcemia in such settings is highly responsive to monoclonal antibodies against RANKL given the role the ligand plays in resorptive hypercalcemia.

Hypercalcemia as the Initial Presentation of Acute T-cell Leukemia/Lymphoma

Adult T-cell leukemia/lymphoma (ATLL) is a T-cell malignancy that generally presents with widespread involvement of lymph nodes, peripheral blood, and/or skin. It is an uncommon malignancy linked to the human T-lymphotropic virus 1 (HTLV-1). Herein, we present a case of ATLL that was diagnosed after a patient presented to our hospital with nonspecific symptoms of fatigue and weakness and was subsequently found to have hypercalcemia secondary to his blood malignancy. We engage in a discussion of the etiology, epidemiology, and management of patients with this rare malignancy as well as the mechanisms that result in hypercalcemia.

Roles of the RANKL-RANK Axis in Immunity-Implications for Pathogenesis and Treatment of Bone Metastasis

A substantial amount patients with cancer will develop bone metastases, with 70% of metastatic prostate and breast cancer patients harboring bone metastasis. Despite advancements in systemic therapies for advanced cancer, survival remains poor for those with bone metastases. The interaction between bone cells and the immune system contributes to a better understanding of the role that the immune system plays in the bone metastasis of cancer. The immune and bone systems share various molecules, including transcription factors, signaling molecules, and membrane receptors, which can stimulate the differentiation and activation of bone-resorbing osteoclasts. The process of cancer metastasis to bone, which deregulates bone turnover and results in bone loss and skeletal-related events (SREs), is also controlled by primary cancer-related factors that modulate the intratumoral microenvironment as well as cellular immune process. The nuclear factor kappa B ligand (RANKL) and the receptor activator of nuclear factor kappa B (RANK) are key regulators of osteoclast development, bone metabolism, lymph node development, and T-cell/dendritic cell communication. RANKL is an osteoclastogenic cytokine that links the bone and the immune system. In this review, we highlight the role of RANKL and RANK in the immune microenvironment and bone metastases and review data on the role of the regulatory mechanism of immunity in bone metastases, which could be verified through clinical efficacy of RANKL inhibitors for cancer patients with bone metastases. With the discovery of the specific role of RANK signaling in osteoclastogenesis, the humanized monoclonal antibody against RANKL, such as denosumab, was available to prevent bone loss, SREs, and bone metastases, providing a unique opportunity to target RANKL/RANK as a future strategy to prevent bone metastases.

The Effect of a Histone Deacetylase Inhibitor (AR-42) and Zoledronic Acid on Adult T-Cell Leukemia/Lymphoma Osteolytic Bone Tumors

Simple Summary

Adult T-cell leukemia (ATL) Leukemia is an aggressive, peripheral blood (T-cell) neoplasm associated with human T-cell leukemia virus type 1 (HTLV-1) infection. Recent studies have implicated dysregulated histone deacetylases in ATL pathogenesis. ATL modulates the bone microenvironment of patients and activates osteoclasts (bone resorbing cells) that cause severe bone loss. The objective of this study was to assess the individual and dual effects of AR-42 (HDACi) and zoledronic acid (Zol) on the growth of ATL cells in vitro and in vivo. AR-42 and Zol reduced the viability of ATL cells in vitro. Additionally, Zol and Zol/AR-42 decreased ATL tumor growth and halted osteolysis in bone tumor xenografts in immunodeficient mice in vivo. Our study suggests that dual targeting of ATL cells (using HDACi) and bone osteoclasts (using bisphosphonates) may be exploited as a valuable approach to reduce bone tumor burden and improve the life quality of ATL patients.

Abstract

Adult T-cell leukemia/lymphoma (ATL) is an intractable disease affecting nearly 4% of Human T-cell Leukemia Virus Type 1 (HTLV-1) carriers. Acute ATL has a unique interaction with bone characterized by aggressive bone invasion, osteolytic metastasis, and hypercalcemia. We hypothesized that dual tumor and bone-targeted therapies would decrease tumor burden in bone, the incidence of metastasis, and ATL-associated osteolysis. Our goal was to evaluate dual targeting of both ATL bone tumors and the bone microenvironment using an anti-tumor HDACi (AR-42) and an osteoclast inhibitor (zoledronic acid, Zol), alone and in combination. Our results showed that AR-42, Zol, and AR-42/Zol significantly decreased the viability of multiple ATL cancer cell lines in vitro. Zol and AR-42/Zol decreased tumor growth in vivo. Zol ± AR-42 significantly decreased ATL-associated bone resorption and promoted new bone formation. AR-42-treated ATL cells had increased mRNA levels of PTHrP, ENPP2 (autotaxin) and MIP-1α, and TAX viral gene expression. AR-42 alone had no significant effect on tumor growth or osteolysis in mice. These findings indicate that Zol adjuvant therapy has the potential to reduce growth of ATL in bone and its associated osteolysis.

Sequential Complications of Hypercalcemia, Necrotizing Granulomatous Vasculitis, and Aplastic Anemia Occurring in One Patient with Angioimmunoblastic T-cell Lymphoma

In this case report of a patient with angioimmunoblastic T-cell lymphoma (AITL), we describe the occurrence of three sequential complications that have been reported uncommonly in this disease subtype. Firstly, the patient developed hypercalcemia due to elevated 1,25-didydroxyvitamin D. Although hypercalcemia in AITL is not rare (1-2% incidence), this case was unusual in that the complication developed when disease appeared stable and symptomatically, he was doing well otherwise. Hypercalcemia surprisingly resolved a few months later at a time when his disease appeared to be progressing. A year later, the patient presented with digital ischemia necessitating partial amputation of a finger. Pathological exam revealed granulomatous vasculitis of small and medium arterioles with infiltrating malignant T lymphocytes. Although skin manifestations are common in AITL, necrotizing granulomatous vasculitis with accompanying tumor cells leading to severe digital ischemia appears rare. Subsequently the patient developed profound pancytopenia with bone marrow confirming severe aplastic anemia. To our knowledge only one other case of aplastic anemia has been reported in a patient with AITL. We discuss the diagnostic and management considerations involved in this patient care and review similar reported cases.

Interferon regulatory factor 4 as a therapeutic target in adult T-cell leukemia lymphoma

Background

Adult T-cell leukemia lymphoma (ATLL) is a chemotherapy-resistant malignancy with a median survival of less than one year that will afflict between one hundred thousand and one million individuals worldwide who are currently infected with human T-cell leukemia virus type 1. Recurrent somatic mutations in host genes have exposed the T-cell receptor pathway through nuclear factor κB to interferon regulatory factor 4 (IRF4) as an essential driver for this malignancy. We sought to determine if IRF4 represents a therapeutic target for ATLL and to identify downstream effectors and biomarkers of IRF4 signaling in vivo.

Results

ATLL cell lines, particularly Tax viral oncoprotein-negative cell lines, that most closely resemble ATLL in humans, were sensitive to dose- and time-dependent inhibition by a next-generation class of IRF4 antisense oligonucleotides (ASOs) that employ constrained ethyl residues that mediate RNase H-dependent RNA degradation. ATLL cell lines were also sensitive to lenalidomide, which repressed IRF4 expression. Both ASOs and lenalidomide inhibited ATLL proliferation in vitro and in vivo. To identify biomarkers of IRF4-mediated CD4 + T-cell expansion in vivo, transcriptomic analysis identified several genes that encode key regulators of ATLL, including interleukin 2 receptor subunits α and β, KIT ligand, cytotoxic T-lymphocyte-associated protein 4, and thymocyte selection-associated high mobility group protein TOX 2.

Conclusions

These data support the pursuit of IRF4 as a therapeutic target in ATLL with the use of either ASOs or lenalidomide.

Mouse model recapitulates the phenotypic heterogeneity of human adult T-cell leukemia/lymphoma in bone

Adult T-cell leukemia/lymphoma has a unique relationship to bone including latency in the marrow, and development of bone invasion, osteolytic tumors and humoral hypercalcemia of malignancy. To study these conditions, we established and characterized a novel mouse model of ATL bone metastasis. Patient-derived ATL cell lines including three that do not express HTLV-1 oncoprotein Tax (ATL-ED, RV-ATL, TL-Om1), an in vitro transformed human T-cell line with high Tax expression (HT-1RV), and an HTLV-1 negative T-cell lymphoma (Jurkat) were injected intratibially into NSG mice, and were capable of proliferating and modifying the bone microenvironment. Radiography, μCT, histopathology, immunohistochemistry, plasma calcium concentrations, and qRT-PCR for several tumor-bone signaling mRNAs were performed. Luciferase-positive ATL-ED bone tumors allowed for in vivo imaging and visualization of bone tumor growth and metastasis over time. ATL-ED and HT-1RV cells caused mixed osteolytic/osteoblastic bone tumors, TL-Om1 cells exhibited minimal bone involvement and aggressive local invasion into the adjacent soft tissues, Jurkat cells proliferated within bone marrow and induced minimal bone cell response, and RV-ATL cells caused marked osteolysis. This mouse model revealed important mechanisms of human ATL bone neoplasms and will be useful to investigate biological interactions, potential therapeutic targets, and new bone-targeted agents for the prevention of ATL metastases to bone.

HTLV-1 viral oncogene HBZ drives bone destruction in adult T cell leukemia

Osteolytic bone lesions and hypercalcemia are common, serious complications in adult T cell leukemia/lymphoma (ATL), an aggressive T cell malignancy associated with human T cell leukemia virus type 1 (HTLV-1) infection. The HTLV-1 viral oncogene HBZ has been implicated in ATL tumorigenesis and bone loss. In this study, we evaluated the role of HBZ on ATL-associated bone destruction using HTLV-1 infection and disease progression mouse models. Humanized mice infected with HTLV-1 developed lymphoproliferative disease and continuous, progressive osteolytic bone lesions. HTLV-1 lacking HBZ displayed only modest delays to lymphoproliferative disease but significantly decreased disease-associated bone loss compared with HTLV-1-infected mice. Gene expression array of acute ATL patient samples demonstrated increased expression of RANKL, a critical regulator of osteoclasts. We found that HBZ regulated RANKL in a c-Fos-dependent manner. Treatment of HTLV-1-infected humanized mice with denosumab, a monoclonal antibody against human RANKL, alleviated bone loss. Using patient-derived xenografts from primary human ATL cells to induce lymphoproliferative disease, we also observed profound tumor-induced bone destruction and increased c-Fos and RANKL gene expression. Together, these data show the critical role of HBZ in driving ATL-associated bone loss through RANKL and identify denosumab as a potential treatment to prevent bone complications in ATL patients.

Neoplastic hematological diseases associated with HTLV-1 infection

Adult cell lymphoma/leukemia (ATLL) is a type of lymphoma consisting of T-cells that are related to infection with the human T lymphotropic virus (HTLV-1). Four clinical forms have been described (leukemic, lymphomatous, chronic, smoldering) and the phenotype corresponds to regulatory CD4+ T cells. The histological characteristics are variable, with neoplastic cells showing a size ranging from small to large and atypical nuclei with irregular contours. A series of genetic and molecular alterations have been described, which partially explain the lymphomagenesis of the neoplasm, some of which are also factors related to the clinical course and overall survival. ATLL is a neoplasm with a poor prognosis, but in recent years new targeted therapies have been designed, with encouraging responses. This neoplasm should continue to be studied to improve treatment and evolution.

MEF-2 isoforms' (A-D) roles in development and tumorigenesis

Myocyte enhancer factor (MEF)-2 plays a critical role in proliferation, differentiation, and development of various cell types in a tissue specific manner. Four isoforms of MEF-2 (A-D) differentially participate in controlling the cell fate during the developmental phases of cardiac, muscle, vascular, immune and skeletal systems. Through their associations with various cellular factors MEF-2 isoforms can trigger alterations in complex protein networks and modulate various stages of cellular differentiation, proliferation, survival and apoptosis. The role of the MEF-2 family of transcription factors in the development has been investigated in various cell types, and the evolving alterations in this family of transcription factors have resulted in a diverse and wide spectrum of disease phenotypes, ranging from cancer to infection. This review provides a comprehensive account on MEF-2 isoforms (A-D) from their respective localization, signaling, role in development and tumorigenesis as well as their association with histone deacetylases (HDACs), which can be exploited for therapeutic intervention.

PD-1 Tumor Suppressor Signaling in T Cell Lymphomas

The inhibitory receptor PD-1 is critical to balancing antigen-induced T cell activation; its inhibition is currently being explored to enhance antitumor T cell immunity with certain successful outcomes. However, PD-1 has also emerged as a central tumor suppressor in T cell lymphomas, where the tumor cell originates from a T cell itself. These aggressive cancers are frequently characterized by oncogenic mutations in T cell receptor (TCR) signaling pathways. PD-1 activity within malignant T cells can negatively regulate the PI3K/AKT and PKCθ/NF-κB tumor survival pathways and PD-1 is frequently inactivated in this human malignancy. This review summarizes current insights into oncogenic T cell signaling, discusses tumor-suppressive functions and mechanisms of PD-1 in T cell lymphomagenesis, and addresses potential unwanted effects caused by PD-1 checkpoint inhibition.

NF-κB-dependent RANKL expression in a mouse model of immature T-cell leukemia

Activation of the receptor activator of nuclear factor-κB (RANK) by its ligand (RANKL) is involved in both solid and hematological malignancies, including multiple myeloma, acute myeloid leukemia and B-cell leukemia. Although RANKL expression has been described in normal T cells, a potential role in T-cell leukemia remains undefined. Here, we used a model of immature T-cell leukemia/lymphoma, the TEL-JAK2 transgenic mice, to assess RANKL expression in leukemic cells and its regulatory mechanisms. We found that Rankl mRNA was significantly overexpressed in leukemic T cells when compared to wild-type thymocytes, their nonmalignant counterparts. Moreover, Rankl mRNA and RANKL surface expression in leukemic cells was induced by T-cell receptor (TCR) signaling activation, dependently on the NF-κB signaling pathway. These results indicate that TCR-activated leukemic T cells express high levels of RANKL and are potential inducers of RANK signaling in microenvironmental cells.

Potential anti-lymphoma effect of M-CSFR inhibitor in adult T-cell leukemia/lymphoma

The c-fms proto-oncogene is also known as macrophage colony stimulating factor receptor (M-CSFR) or colony-stimulating factor-1 receptor (CSF-1R), and is expressed on several types of malignant tumor cells and myeloid cells. In the present study, we found that overexpression of M-CSFR was present in adult T-cell leukemia/lymphoma (ATLL) cases. M-CSFR signaling was associated with lymphoma cell proliferation, and M-CSFR inhibition induced apoptosis in lymphoma cells. The ATLL cell line ATL-T expressed M-CSF/CSF-1 and interleukin (IL)-34, which are both M-CSFR ligands. M-CSF and IL-34 expression was seen in ATLL cases, and co-expression of these ligands was detected in 11 of 13 ATLL cases. M-CSFR inhibition suppressed programmed death-1 and -2 ligand in ATL-T cells and macrophages stimulated with conditioned medium from ATL-T cells. Thus, an M-CSFR inhibitor may be useful as additional therapy against ATLL due to direct and indirect mechanisms.

HTLV-1, ATLL, severe hypercalcaemia and HIV-1 co-infection: an overview

HIV and HTLV (Human T-ymphotropic Virus) are the only known retroviruses responsible for causing infection in humans. HTLV-1 and HIV-1 are frequent co-pathogens, however, despite its potential for accelerated progression of HIV disease and the risk of developing adult T-cell lymphoma/leukemia (ATLL), HTLV-1 is seldom considered for investigation in the HIV-1 positive individual. Severe/refractory hypercalcaemia, unresponsive to conventional calcium lowering therapy may complicate up to 70% of cases of ATLL. In addition, HTLV-1 and ATLL have both been associated with a rise in dysfunctional CD4 lymphocytes, thereby conveying a false sense of immune competence in the HIV-1 infected individual.

HTLV-1, ATLL, refractory hypercalcaemia and HIV-1 co-infection

Adult T-cell lymphoma/leukemia (ATLL) is a rare tumour of T-lymphocytes that is associated with human T-lymphotrophic virus type 1 (HTLV-1) infection as well as severe/refractory hypercalcaemia. Human immunodefficiency virus type 1 (HIV-1) infected individuals are at increased risk of acquiring co-infection with HTLV-1. We present the case of a 37 -year -old HIV-1 positive and antiretroviral therapy naive woman who was admitted to the ICU with delirium, a generalised maculopapular rash, severe hypercalcaemia of 4.48 mmol/L (normal < 2.7 mmol/L) and a positive HTLV-1 serology. The diagnosis of ATLL was confirmed on biopsy. Her hypercalcaemic state proved refractory to conventional therapy, but was rapidly corrected with a modified haemodialysis technique using a dialysate with a low low-calcium concentration.

An activating mutation of interferon regulatory factor 4 (IRF4) in adult T-cell leukemia

The human T-cell leukemia virus-1 (HTLV-1) oncoprotein Tax drives cell proliferation and resistance to apoptosis early in the pathogenesis of adult T-cell leukemia (ATL). Subsequently, probably as a result of specific immunoediting, Tax expression is down-regulated and functionally replaced by somatic driver mutations of the host genome. Both amplification and point mutations of interferon regulatory factor 4 (IRF4) have been previously detected in ATL., K59R is the most common single-nucleotide variation of IRF4 and is found exclusively in ATL. High-throughput whole-exome sequencing revealed recurrent activating genetic alterations in the T-cell receptor, CD28, and NF-κB pathways. We found that IRF4, which is transcriptionally activated downstream of these pathways, is frequently mutated in ATL. IRF4 RNA, protein, and IRF4 transcriptional targets are uniformly elevated in HTLV-1-transformed cells and ATL cell lines, and IRF4 was bound to genomic regulatory DNA of many of these transcriptional targets in HTLV-1-transformed cell lines. We further noted that the K59R IRF4 mutant is expressed at higher levels in the nucleus than WT IRF4 and is transcriptionally more active. Expression of both WT and the K59R mutant of IRF4 from a constitutive promoter in retrovirally transduced murine bone marrow cells increased the abundance of T lymphocytes but not myeloid cells or B lymphocytes in mice. IRF4 may represent a therapeutic target in ATL because ATL cells select for a mutant of IRF4 with higher nuclear expression and transcriptional activity, and overexpression of IRF4 induces the expansion of T lymphocytes in vivo.

HTLV-1 viral oncogene HBZ induces osteolytic bone disease in transgenic mice

Adult T-cell leukemia/lymphoma (ATL) is an aggressive T cell malignancy that occurs in HTLV-1 infected patients. Most ATL patients develop osteolytic lesions and hypercalcemia of malignancy, causing severe skeletal related complications and reduced overall survival. The HTLV-1 virus encodes 2 viral oncogenes, Tax and HBZ. Tax, a transcriptional activator, is critical to ATL development, and has been implicated in pathologic osteolysis. HBZ, HTLV-1 basic leucine zipper transcription factor, promotes tumor cell proliferation and disrupts Wnt pathway modulators; however, its role in ATL induced osteolytic bone loss is unknown. To determine if HBZ is sufficient for the development of bone loss, we established a transgenic Granzyme B HBZ (Gzmb-HBZ) mouse model. Lymphoproliferative disease including tumors, enlarged spleens and/or abnormal white cell counts developed in two-thirds of Gzmb-HBZ mice at 18 months. HBZ positive cells were detected in tumors, spleen and bone marrow. Importantly, pathologic bone loss and hypercalcemia were present at 18 months. Bone-acting factors were present in serum and RANKL, PTHrP and DKK1, key mediators of hypercalcemia and bone loss, were upregulated in Gzmb-HBZ T cells. These data demonstrate that Gzmb-HBZ mice model ATL bone disease and express factors that are current therapeutic targets for metastatic and bone resident tumors.

Adult T-cell leukemia: molecular basis for clonal expansion and transformation of HTLV-1-infected T cells

Adult T-cell leukemia (ATL) is an aggressive T-cell malignancy caused by human T-cell leukemia virus type 1 (HTLV-1) that develops through a multistep carcinogenesis process involving 5 or more genetic events. We provide a comprehensive overview of recently uncovered information on the molecular basis of leukemogenesis in ATL. Broadly, the landscape of genetic abnormalities in ATL that include alterations highly enriched in genes for T-cell receptor-NF-κB signaling such as PLCG1, PRKCB, and CARD11 and gain-of function mutations in CCR4 and CCR7 Conversely, the epigenetic landscape of ATL can be summarized as polycomb repressive complex 2 hyperactivation with genome-wide H3K27 me3 accumulation as the basis of the unique transcriptome of ATL cells. Expression of H3K27 methyltransferase enhancer of zeste 2 was shown to be induced by HTLV-1 Tax and NF-κB. Furthermore, provirus integration site analysis with high-throughput sequencing enabled the analysis of clonal composition and cell number of each clone in vivo, whereas multicolor flow cytometric analysis with CD7 and cell adhesion molecule 1 enabled the identification of HTLV-1-infected CD4+ T cells in vivo. Sorted immortalized but untransformed cells displayed epigenetic changes closely overlapping those observed in terminally transformed ATL cells, suggesting that epigenetic abnormalities are likely earlier events in leukemogenesis. These new findings broaden the scope of conceptualization of the molecular mechanisms of leukemogenesis, dissecting them into immortalization and clonal progression. These recent findings also open a new direction of drug development for ATL prevention and treatment because epigenetic marks can be reprogrammed. Mechanisms underlying initial immortalization and progressive accumulation of these abnormalities remain to be elucidated.

Vitamin D-Mediated Hypercalcemia: Mechanisms, Diagnosis, and Treatment

Hypercalcemia occurs in up to 4% of the population in association with malignancy, primary hyperparathyroidism, ingestion of excessive calcium and/or vitamin D, ectopic production of 1,25-dihydroxyvitamin D [1,25(OH)₂D], and impaired degradation of 1,25(OH)₂D. The ingestion of excessive amounts of vitamin D₃ (or vitamin D₂) results in hypercalcemia and hypercalciuria due to the formation of supraphysiological amounts of 25-hydroxyvitamin D [25(OH)D] that bind to the vitamin D receptor, albeit with lower affinity than the active form of the vitamin, 1,25(OH)₂D, and the formation of 5,6-trans 25(OH)D, which binds to the vitamin D receptor more tightly than 25(OH)D. In patients with granulomatous disease such as sarcoidosis or tuberculosis and tumors such as lymphomas, hypercalcemia occurs as a result of the activity of ectopic 25(OH)D-1-hydroxylase (CYP27B1) expressed in macrophages or tumor cells and the formation of excessive amounts of 1,25(OH)₂D. Recent work has identified a novel cause of non-PTH-mediated hypercalcemia that occurs when the degradation of 1,25(OH)₂D is impaired as a result of mutations of the 1,25(OH)₂D-24-hydroxylase cytochrome P450 (CYP24A1). Patients with biallelic and, in some instances, monoallelic mutations of the CYP24A1 gene have elevated serum calcium concentrations associated with elevated serum 1,25(OH)₂D, suppressed PTH concentrations, hypercalciuria, nephrocalcinosis, nephrolithiasis, and on occasion, reduced bone density. Of interest, first-time calcium renal stone formers have elevated 1,25(OH)₂D and evidence of impaired 24-hydroxylase-mediated 1,25(OH)₂D degradation. We will describe the biochemical processes associated with the synthesis and degradation of various vitamin D metabolites, the clinical features of the vitamin D-mediated hypercalcemia, their biochemical diagnosis, and treatment.

RANK-RANKL signalling in cancer

Oncogenic events combined with a favourable environment are the two main factors in the oncological process. The tumour microenvironment is composed of a complex, interconnected network of protagonists, including soluble factors such as cytokines, extracellular matrix components, interacting with fibroblasts, endothelial cells, immune cells and various specific cell types depending on the location of the cancer cells (e.g. pulmonary epithelium, osteoblasts). This diversity defines specific "niches" (e.g. vascular, immune, bone niches) involved in tumour growth and the metastatic process. These actors communicate together by direct intercellular communications and/or in an autocrine/paracrine/endocrine manner involving cytokines and growth factors. Among these glycoproteins, RANKL (receptor activator nuclear factor-κB ligand) and its receptor RANK (receptor activator nuclear factor), members of the TNF and TNFR superfamilies, have stimulated the interest of the scientific community. RANK is frequently expressed by cancer cells in contrast with RANKL which is frequently detected in the tumour microenvironment and together they participate in every step in cancer development. Their activities are markedly regulated by osteoprotegerin (OPG, a soluble decoy receptor) and its ligands, and by LGR4, a membrane receptor able to bind RANKL. The aim of the present review is to provide an overview of the functional implication of the RANK/RANKL system in cancer development, and to underline the most recent clinical studies.

Two cases of primary adult T-cell leukemia/lymphoma of bone: case reports and a review of the literature

Primary bone lymphomas comprise <1 % of all malignant lymphomas, and there have been only a limited number of reports on primary adult T-cell leukemia/lymphoma (ATLL) of bone. Here, we report two cases of primary ATLL of bone. The first case was a 41-year-old woman with multiple bone tumors. She was diagnosed with ATLL of the skull through biopsy and treated with chemotherapy. Although the bone lesions showed transient improvement, the subsequent central nervous system (CNS) invasion of ATLL occurred and she died 7 months after diagnosis. The second case was a 65-year-old man with right coxodynia. He was diagnosed with ATLL through right femoral biopsy, and the lesion improved with chemotherapy. However, CNS invasion of ATLL developed during chemotherapy, and he died 10 months after diagnosis. Both the patients with primary ATLL of the bone reported here experienced CNS invasion. Thus, ATLL treatment should aim to prevent CNS invasion at an early stage.

Mechanisms of enhanced osteoclastogenesis in girls and young women with Turner's Syndrome

Subjects with hypergonadotropic hypogonadism due to Turner's syndrome show low cortical mineral density, osteoporosis and risk of fractures. It is not clear if this bone fragility derives from chromosomal abnormalities or is the result of inadequate bone formation due to estrogen deficiency. The aim of this study was to investigate the cellular mechanisms underlying bone fragility in subjects with Turner's syndrome before induction of puberty and after hormonal replacement therapy (HRT). For this purpose, we have evaluated the osteoclastogenic potential of non-fractioned and T-cell depleted cultures of peripheral blood mononuclear cells (PBMCs) belonging to girls with Turner's syndrome who had not been treated with HRT yet, girls and young women who were on HRT and age-matched controls. Untreated subjects showed high FSH serum levels, whereas the other subjects displayed normal FSH serum levels. T-cell immunophenotype was analyzed through flow cytometry. Biochemical and DXA analyses were performed. Spontaneous osteoclastogenesis in non-fractioned and T-cell depleted cultures of PBMC belonging to girls with high FSH levels was more evident than in cultures of subjects with normal FSH levels. In the former, osteoclastogenesis was sustained by monocytes expressing high levels of c-fms, TNF-α and RANK, and T-cells producing high RANKL and TNF-α; in the latter it was supported by T-cells expressing high RANKL levels. CD4(+)CD25(high) T-cells were reduced in all subjects, whereas CD3(+)/CD16(+)/CD56(+) NKT-cells were increased in those with high FSH levels. High RANKL and CTX levels were detected in the sera. Bone impairment was already detectable by DXA in subjects aged under 10, although it became more evident with aging. In conclusion, our results demonstrated that bone fragility in subjects with Turner's syndrome is associated to enhanced osteoclastogenesis. This process seems to be due to high FSH serum levels before HRT, whereas it is caused by high RANKL during HRT.

Potential role of the OPG/RANK/RANKL axis in prostate cancer invasion and bone metastasis

Receptor activator of NF-κB (RANK), RANK ligand (RANKL) and osteoprotegerin (OPG) are key regulators of bone metabolism under both normal and pathological conditions, including prostate cancer (PCa) bone metastases. However, little is known concerning the expression and function of these regulators in prostate tumor samples and PCa cells and their correlation with invasion and bone metastasis. In the present study, we determined the expression of RANK, RANKL and OPG in 3 human PCa cell lines and 40 PCa patient samples by immunohistochemistry and enzyme-linked immunosorbent assay (ELISA). As controls, samples from 20 patients with benign prostate hyperplasia (BPH) and normal prostate epithelial RWPE2 cells were also included in the analyses. The effects of soluble RANKL (sRANKL) and OPG as well as RANK knockdown on PCa invasion were examined in Transwell assays. Immunohistochemical staining detected little RANK, OPG and RANKL expression in hyperplasia prostate while the percentages of positivity were increased to 50, 45 and 52.5%, respectively, in prostate tumor tissues. OPG and sRANKL levels in the prostate tumor samples as measured by ELISA were ~10-fold that in the BPHs (P<0.01) and the levels were higher in aggressive tumors than non-aggressive ones (P<0.05). The sRANKL level in the serum of PCa patients was the same as that in the patients with BPH, yet the serum OPG levels correlated with the tissue levels (R2=0.620, P<0.01, which both showed a 10-fold increase in PCa over BPH (P<0.01) with higher levels in aggressive PCa than non-aggressive ones (P<0.05). Consistent with the tissue analyses, expression levels of RANK mRNA and protein were detected in multiple human PCa cell lines by RT-PCR and western blotting, respectively. The treatment of PCa cells with RANKL significantly increased the number of invaded cells (P<0.01), which was suppressed by the decoy receptor OPG. RANK siRNA transfection dramatically dampened the stimulatory effect of RANKL on PCa cell invasion. Our findings indicate that the expression of RANK, RANKL and OPG may be used as diagnostic markers to identify patients at high risk for aggressive PCa and that the effective suppression of PCa cell migration by OPG via the blockage of RANKL activity represents a potential therapeutic strategy for interfering with prostate tumor metastasis and progression to bone.

Bone disease in multiple myeloma: pathophysiology and management

Myeloma bone disease (MBD) is a devastating complication of multiple myeloma (MM). More than 80% of MM patients suffer from destructive bony lesions, leading to pain, fractures, mobility issues, and neurological deficits. MBD is not only a main cause of disability and morbidity in MM patients but also increases the cost of management. Bone destruction and lack of bone formation are main factors in the development of MBD. Some novel factors are found to be involved in the pathogenesis of MBD, eg, receptor activator of nuclear factor kappa-B ligand (RANKL), osteoprotegerin (OPG) system (RANKL/OPG), Wingless (Wnt), dickkopf-1 (Wnt/DKK1) pathway. The addition of novel agents in the treatment of MM, use of bisphosphonates and other supportive modalities such as radiotherapy, vertebroplasty/kyphoplasty, and surgical interventions, all have significant roles in the treatment of MBD. This review provides an overview on the pathophysiology and management of MBD.

Role of osteoclasts in regulating hematopoietic stem and progenitor cells

Bone marrow (BM) cavities are utilized for hematopoiesis and to maintain hematopoietic stem cells (HSCs). HSCs have the ability to self-renew as well as to differentiate into multiple different hematopoietic lineage cells. HSCs produce their daughter cells throughout the lifespan of individuals and thus, maintaining HSCs is crucial for individual life. BM cavities provide a specialized microenvironment termed “niche” to support HSCs. Niches are composed of various types of cells such as osteoblasts, endothelial cells and reticular cells. Osteoclasts are unique cells which resorb bones and are required for BM cavity formation. Loss of osteoclast function or differentiation results in inhibition of BM cavity formation, an osteopetrotic phenotype. Osteoclasts are also reportedly required for hematopoietic stem and progenitor cell (HSPC) mobilization to the periphery from BM cavities. Thus, lack of osteoclasts likely results in inhibition of HSC maintenance and HSPC mobilization. However, we found that osteoclasts are dispensable for hematopoietic stem cell maintenance and mobilization by using three independent osteoclast-less animal models. In this review, I will discuss the roles of osteoclasts in hematopoietic stem cell maintenance and mobilization.

Adult T-cell leukemia cells overexpress Wnt5a and promote osteoclast differentiation

Adult T-cell leukemia/lymphoma (ATL) is etiologically linked to infection with the human T-cell leukemia/lymphoma virus type 1 (HTLV-I). ATL is classified into 4 distinct clinical diseases: acute, lymphoma, chronic, and smoldering. Acute ATL is the most aggressive form, representing 60% of cases and has a 4-year survival of < 5%. A frequent complication and cause of death in acute ATL patients is the presence of lytic bone lesions and hypercalcemia. We analyzed the Wnt/β-catenin pathway because of its common role in cancer and bone remodeling. Our study demonstrated that ATL cells do not express high levels of β-catenin but displayed high levels of LEF-1/TCF genes along with elevated levels of β-catenin (LEF-1/TCF target genes) responsive genes. By profiling Wnt gene expression, we discovered that ATL patient leukemia cells shifted expression toward the noncanonical Wnt pathway. Interestingly, ATL cells overexpressed the osteolytic-associated genes-Wnt5a, PTHLH, and RANKL. We further show that Wnt5a secreted by ATL cells favors osteoclast differentiation and expression of RANK. Our results suggest that Wnt5a is a major contributing factor to the increase in osteolytic bone lesions and hypercalcemia found in ATL patients. Anti-Wnt5a therapy may prevent or reduce osteolytic lesions found in ATL patients and improve therapy outcome.

Molecular hallmarks of adult T cell leukemia

The molecular hallmarks of adult T cell leukemia (ATL) comprise outstanding deregulations of signaling pathways that control the cell cycle, resistance to apoptosis, and proliferation of leukemic cells, all of which have been identified by early excellent studies. Nevertheless, we are now confronted the therapeutic difficulties of ATL that is a most aggressive T cell leukemia/lymphoma. Using next-generation strategies, emerging molecular characteristics such as specific surface markers and an additional catalog of signals affecting the fate of leukemic cells have been added to the molecular hallmarks that constitute an organizing principle for rationalizing the complexities of ATL. Although human T cell leukemia virus type 1 is undoubtedly involved in ATL leukemogenesis, most leukemic cells do not express the viral protein Tax. Instead, cellular gene expression changes dominate homeostasis disorders of infected cells and characteristics of ATL. In this review, we summarize the state of the art of ATL molecular pathology, which supports the biological properties of leukemic cells. In addition, we discuss the recent discovery of two molecular hallmarks of potential generality; an abnormal microRNA pattern and epigenetic reprogramming, which strongly involve the imbalance of the molecular network of lymphocytes. Global analyses of ATL have revealed the functional impact of crosstalk between multifunctional pathways. Clinical and biological studies on signaling inhibitory agents have also revealed novel oncogenic drivers that can be targeted in future. ATL cells, by deregulation of such pathways and their interconnections, may become masters of their own destinies. Recognizing and understanding of the widespread molecular applicability of these concepts will increasingly affect the development of novel strategies for treating ATL.

Regulators of osteoclast differentiation and cell-cell fusion

Osteoclasts are multinuclear giant cells derived from osteoclast/macrophage/dendritic cell common progenitor cells. The most characteristic feature of osteoclasts is multinucleation resulting from cell-cell fusion of mononuclear osteoclasts. Osteoclast cell-cell fusion is considered essential for re-organization of the cytoskeleton, such as the actin-ring and ruffled boarder to seal the resorbing area and to secret protons, respectively, to resorb bone; the fusion process is thus critical for osteoclast function. Various molecules, such as E-cadherin and macrophage fusion receptor (MFR), have been identified as regulators of osteoclast or macrophage cell-cell fusion. Laboratory production of osteoclasts used to be performed in a co-culture of osteoclast progenitors with osteoblastic cells, but recent advances in the identification of nuclear factor of kappa B ligand (RANKL) enabled the isolation of osteoclast-specific molecules involving osteoclast cell-cell fusion and differentiation regulators from purified osteoclast mRNA, since osteoclasts can be formed without osteoblasts. The essential cell-cell fusion regulator, dendritic cell-specific transmembrane protein (DC-STAMP), was isolated by a cDNA subtractive screen between mononuclear macrophages and RANKL-induced multinuclear osteoclasts. The cell-cell fusion of osteoclasts and foreign body giant cells (FBGCs) was completely abrogated in DC-STAMP-deficient mice in vivo and in vitro. Bone resorbing activity was significantly reduced but was still detected in DC-STAMP-deficient osteoclasts. DC-STAMP expression is positively regulated by two transcriptional factors: nuclear factor of activated T cells 1 (NFATc1) and c-Fos, both of which are essential for osteoclast differentiation. Furthermore, a novel osteoclastogenesis-regulating pathway involving two transcriptional repressors [B cell lymphoma 6 (Bcl6) and B lymphocyte-induced maturation protein 1 (Blimp1)] under RANKL stimulation has been discovered. The expression of osteoclastic genes such as DC-STAMP, NFATc1, and Cathepsin K, as well as osteoclast differentiation, was inhibited by Bcl6. Bcl6-deficient mice showed enhanced osteoclastogenesis and reduced bone mass, whereas osteoclast-specific Blimp1-conditional knockout mice showed elevated Bcl6 expression, osteoclastic gene expression, and osteoclast differentiation and increased bone mass. In this review, recent advances in our understanding of the regulators of osteoclast differentiation and cell-cell fusion are discussed.

Clinical Trials and Treatment of ATL

ATL is a distinct peripheral T-lymphocytic malignancy associated with human T-cell lymphotropic virus type I (HTLV-1). The diversity in clinical features and prognosis of patients with this disease has led to its subtype-classification into four categories, acute, lymphoma, chronic, and smoldering types, defined by organ involvement, and LDH and calcium values. In case of acute, lymphoma, or unfavorable chronic subtypes (aggressive ATL), intensive chemotherapy like the LSG15 regimen (VCAP-AMP-VECP) is usually recommended if outside of clinical trials, based on the results of a phase 3 trial. In case of favorable chronic or smoldering ATL (indolent ATL), watchful waiting until disease progression has been recommended, although the long-term prognosis was inferior to those of, for instance, chronic lymphoid leukemia. Retrospective analysis suggested that the combination of interferon alpha and zidovudine was apparently promising for the treatment of ATL, especially for types with leukemic manifestation. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is also promising for the treatment of aggressive ATL possibly reflecting graft versus ATL effect. Several new agent trials for ATL are ongoing and in preparation, including a defucosylated humanized anti-CC chemokine receptor 4 monoclonal antibody, IL2-fused with diphtheria toxin, histone deacetylase inhibitors, a purine nucleoside phosphorylase inhibitor, a proteasome inhibitor, and lenalidomide.

Effects of parathyroid hormone-related protein and macrophage inflammatory protein-1α in Jurkat T-cells on tumor formation in vivo and expression of apoptosis regulatory genes in vitro

Parathyroid hormone-related protein (PTHrP) and macrophage inflammatory protein-1α (MIP-1α) have been implicated in the pathogenesis of adult T-cell leukemia/lymphoma, but their effects on T-cells have not been well studied. Here we analyzed the functions of PTHrP and MIP-1α on T-cell growth and death both in vitro and in vivo by overexpressing either factor in human Jurkat T-cells. PTHrP or MIP-1α did not affect Jurkat cell growth in vitro, but PTHrP increased their sensitivity to apoptosis. Importantly, PTHrP and MIP-1α decreased both tumor incidence and growth in vivo. To investigate possible mechanisms, polymerase chain reaction (PCR) arrays and real-time reverse transcription (RT)-PCR assays were performed. Both PTHrP and MIP-1α increased the expression of several factors including signal transducer and activator of transcription 4, tumor necrosis factor α, receptor activator of nuclear factor κB ligand and death-associated protein kinase 1, and decreased the expression of inhibitor of DNA binding 1, interferon γ and CD40 ligand in Jurkat cells. In addition, MIP-1α also increased the expression of transcription factor AP-2α and PTHrP increased expression of the vitamin D3 receptor. These data demonstrate that PTHrP and MIP-1α exert a profound antitumor effect presumably by increasing the sensitivity to apoptotic signals through modulation of transcription and apoptosis factors in T-cells.

Pathogenesis of Metastatic Calcification and Acute Pancreatitis in Adult T-Cell Leukemia under Hypercalcemic State

Human T-cell leukemia virus type-1 (HTLV-1) is the causative agent of adult T-cell leukemia (ATL). Hypercalcemia is common in patients with ATL. These patients rarely develop metastatic calcification and acute pancreatitis. The underlying pathogenesis of this condition is osteoclast hyperactivity with associated overproduction of parathyroid hormone-related protein, which results in hypercalcemia in association with bone demineralization. The discovery of the osteoclast differentiation factor receptor activator of nuclear factor-κB ligand (RANKL), its receptor RANK, and its decoy receptor osteoprotegerin (OPG), enhanced our understanding of the mechanisms of ATL-associated hypercalcemia. Macrophage inflammatory protein-1-α, tumor necrosis factor-α, interleukin-1, and interleukin-6 are important molecules that enhance the migration and differentiation of osteoclasts and the associated enhanced production of RANKL for osteoblast formation. In this paper, we focus on metastatic calcification and acute pancreatitis in ATL, highlighting recent advances in the understanding of the molecular role of the RANKL/RANK/OPG system including its interaction with various cytokines and calciotropic hormones in the regulation of osteoclastogenesis for bone resorption in hypercalcemic ATL patients.

Osteoprotegerin and RANKL in the pathogenesis of rheumatoid arthritis-induced osteoporosis

Osteoporosis represents an important cause of morbidity in adult rheumatoid arthritis (RA) patients who exhibit increased fracture risk. It is thought that osteoclast and its dysfunction which mediated by many cytokines are the principal pathogenesis of this bone disease, although the mechanisms are still not fully understood. Osteoprotegerin (OPG) and receptor activator of nuclear factor-kappa B ligand (RANKL) have been revealed in the pathogenesis of primary osteoporosis and other metabolic bone diseases. Thus, the aim of this study was to investigate the possible role of the OPG/RANKL system in RA-related bone loss. A total of 64 Chinese patients with RA and 60 healthy control subjects were involved. Serum levels of OPG and RANKL were measured by ELISA. BMD of nondominant forearm, lumbar spine(L(1-4)) and proximal femur, including femoral neck, Wards triangle, greater trochanter were assessed using dual-energy X-ray absorptiometry. RA patients had a higher incidence of osteoporosis (23/64, 35.9%) than that in healthy controls (9/60, 15.0%) (P < 0.0001). They displayed lower BMD values than controls at positions of all detected region. Compared with healthy controls, RA group showed significantly higher serum levels of RANKL (48.4 ± 12.5 vs. 23.0 ± 11.2 pmol/l, P < 0.0001), lower serum levels of OPG (106.2 ± 40.6 vs. 231.6 ± 65.6 pg/ml, P < 0.0001), and OPG/RANKL ratio (2.4 ± 0.7 vs. 7.0 ± 1.1, P < 0.0001). Multiple linear regression analysis revealed that in RA group, plasma rheumatoid factor concentration (β = -0.187, P = 0.031), swollen joint count (β = 0.567, P = 0.029), BMD at forearm (β = 0.324, P = 0.002), femoral Wards triangle (β = 0.370, P < 0.0001), and lumbar spine (β = 0.313, P = 0.003) were the contributors for serum OPG (R ( 2 ) = 0.718, P < 0.0001). Age (β = 0.241, P = 0.042) and BMD at femoral Wards triangle (β = -0.441, P < 0.0001) and lumbar spine (β = -0.320, P = 0.013) were the determinants for serum RANKL (R ( 2 ) = 0.616, P < 0.0001), while swollen joint count (β = 1.029, P = 0.019) and BMD at femoral neck (β = 0.285, P = 0.042) for serum OPG/RANKL ratio (R ( 2 ) = 0.279, P < 0.011). Analysis of logistic regression showed age (P = 0.004, OR = 1.156, 95% CI: 1.047-1.276) and the level of C-reactive protein (P = 0.028, OR = 1.019, CI 95%: 1.002-1.036) in peripheral blood of RA were the risk factors for the occurrence of osteoporosis in RA, while OPG/RANKL ratio (P = 0.007, OR = 0.035, CI 95%: 0.003-0.400) was the unique protective factor. These data suggest that, in Chinese RA patients, an altered modulation of the OPG/RANKL system resulting in increased RANKL and decreased OPG in peripheral blood, could contribute to the bone loss characteristic and the generation of osteoporosis in these patients. Changes of ratio of OPG/RANKL might be a protective mechanism against the accelerated bone loss in RA.

Over-expression of CCL3 MIP-1alpha in a blastoid mantle cell lymphoma with hypercalcemia

We analyzed a case with the blastoid variant of mantle cell lymphoma (MCL-BV), a rare subtype of B-cell lymphoma, presenting with marked hypercalcemia at diagnosis. Enzyme-linked immunosorbent assay (ELISA) showed elevated serum levels of interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), macrophage inflammatory protein-1alpha (MIP-1alpha), and type I collagen telopeptide, but not parathyroid hormone, calcitriol or parathyroid hormone-related peptide at diagnosis, suggesting local osteoclastic hypercalcemia in this case. By reverse transcription polymerase chain reaction (RT-PCR) analysis, we found predominant expression of mRNA for MIP-1alpha in addition to those for receptor-activator of nuclear-factor kappa B ligand (RANKL), TNF-alpha, and IL-6 in lymphoma cells obtained from the patient. Furthermore, recombinant MIP-1alpha significantly stimulated (3)H-thymidine uptake by isolated MCL cells in vitro. Treatment with intravenous fluids, bisphosphonate, and methylprednisolone followed by combination chemotherapy promptly corrects the hypercalcemia and successfully induced complete remission, which was accompanied by a decrease of these cytokines in the serum, including MIP-1alpha. In the present case, MIP-1alpha, an osteoclast-activating factor produced by mantle lymphoma cells, may contribute to the development of hypercalcemia. It likely acts through RANKL expression in tumor cells and/or stroma cells, as indicated in multiple myeloma (MM) and adult T-cell leukemia/lymphoma (ATLL). Furthermore, MIP-1alpha is also involved in the development of an aggressive phenotype on MCL by stimulating proliferation of these lymphoma cells. In summary, the present study demonstrated that MIP-1alpha is an important factor in the development of both hypercalcemia and an aggressive phenotype in some types of B-cell lymphoma.

Osteolytic bone resorption in adult T-cell leukemia/lymphoma

Adult T-cell leukemia/lymphoma (ATLL) is caused by human T lymphotropic virus type 1 (HTLV-1). Patients with ATLL frequently develop humoral hypercalcemia of malignancy (HHM) resulting from increased osteoclastic bone resorption. Our goal was to investigate the mechanisms of ATLL-induced osteoclastic bone resorption. Murine calvaria co-cultured with HTLV-1-infected cells directly or conditioned media from cell cultures had increased osteoclast activity that was dependent on RANKL, indicating that factors secreted from ATLL cells had a stimulatory effect on bone resorption. Factors released from resorbing bone stimulated proliferation of HTLV-1-infected T-cells. Parathyroid hormone-related protein (PTHrP) and macrophage inflammatory protein-1alpha (MIP-1alpha), both osteoclast stimulators, were expressed in HTLV-1-infected T-cell lines. Interestingly, when HTLV-1-infected T-cells were co-cultured with pre-osteoblasts, the expression of osteoprotegerin (OPG), an osteoclast inhibitory factor, was significantly down-regulated in the pre-osteoblasts. When OPG was added into the ex vivo osteoclastogenesis assay induced by HTLV-1-infected T-cells, osteoclastogenesis was strongly inhibited. In addition, HTLV-1-infected T-cells inhibited expression of early osteoblast genes and induced late genes. These regulators will serve as future therapeutic targets for the treatments of HHM in ATLL.

Expression of a protein involved in bone resorption, Dkk1, is activated by HTLV-1 bZIP factor through its activation domain

Background

Human T-cell leukemia virus type 1 (HTLV-1) is the etiologic agent of adult T-cell leukemia, a malignancy characterized by uncontrolled proliferation of virally-infected CD4+ T-cells. Hypercalcemia and bone lesions due to osteoclast-mediated bone resorption are frequently associated with more aggressive forms of the disease. The HTLV-1 provirus contains a unique antisense gene that expresses HTLV-1 basic leucine zipper (bZIP) factor (HBZ). HBZ is localized to the nucleus where it regulates levels of transcription by binding to certain cellular transcriptional regulators. Among its protein targets, HBZ forms a stable complex with the homologous cellular coactivators, p300 and CBP, which is modulated through two N-terminal LXXLL motifs in the viral protein and the conserved KIX domain in the coactivators.

Results

To determine the effects of these interactions on transcription, we performed a preliminary microarray analysis, comparing levels of gene expression in cells with wild-type HBZ versus cells with HBZ mutated in its LXXLL motifs. DKK1, which encodes the secreted Wnt signaling inhibitor, Dickkopf-1 (Dkk1), was confirmed to be transcriptionally activated by HBZ, but not its mutant. Dkk1 plays a major role in the development of bone lesions caused by multiple myeloma. In parallel with the initial findings, activation of Dkk1 expression by HBZ was abrogated by siRNA-mediated knockdown of p300/CBP or by a truncated form of p300 containing the KIX domain. Among HTLV-1-infected T-cell lines tested, the detection of Dkk1 mRNA partially correlated with a threshold level of HBZ mRNA. In addition, an uninfected and an HTLV-1-infected T-cell line transfected with an HBZ expression vector exhibited de novo and increased DKK1 transcription, respectively. In contrast to HBZ, The HTLV-1 Tax protein repressed Dkk1 expression.

Conclusions

These data indicate that HBZ activates Dkk1 expression through its interaction with p300/CBP. However, this effect is limited in HTLV-1-infected T-cell lines, which in part, may be due to suppression of Dkk1 expression by Tax. Consequently, the ability of HBZ to regulate expression of Dkk1 and possibly other cellular genes may only be significant during late stages of ATL, when Tax expression is repressed.

Haematological emergencies managing hypercalcaemia in adults and children with haematological disorders

Hypercalcaemia is a common metabolic complication of malignant disease often requiring emergency intervention. Although it is more frequently associated with solid tumours, malignancy-associated hypercalcaemia (MAH) is seen in a significant number of patients with blood diseases. Its association with myeloma and adult T-cell leukaemia/lymphoma is well recognized but the incidence of hypercalcaemia in other haematological neoplasms, affecting adults and children, is less clearly defined. Haematologists need to be familiar with the clinical manifestations of, the differential diagnosis to be considered and the most effective management strategies that are currently available for MAH. The key components of management of MAH include aggressive rehydration, specific therapy to inhibit bone resorption and, crucially, treatment of the underlying malignancy. Bisphosphonates have revolutionized the management of MAH over the last 20 years, however the elucidation of molecular pathways implicated in MAH is facilitating the development of more targeted approaches to treatment.

Osteoclastogenesis in children with 21-hydroxylase deficiency on long-term glucocorticoid therapy: the role of receptor activator of nuclear factor-kappaB ligand/osteoprotegerin imbalance

CONTEXT

Children with 21-hydroxylase deficiency (21-OHD) need chronic glucocorticoid (cGC) therapy to replace congenital deficit of cortisol synthesis. cGC therapy is the most frequent and severe form of drug-induced osteoporosis, and different mechanisms have been proposed to explain its pathogenesis.

OBJECTIVE

We investigated the osteoclastogenic potential of peripheral blood mononuclear cells (PBMCs) from 18 children with 21-OHD on cGC therapy and 25 controls who never received GCs. We also evaluated the presence of circulating osteoclast precursors (OCPs) and the role of T cells in osteoclast formation.

RESULTS

Spontaneous osteoclastogenesis, without adding macrophage-colony stimulating factor and receptor activator of nuclear factor-kappaB ligand (RANKL), and significantly higher osteoclasts resorption activity occurred in 21-OHD patients. Conversely, macrophage-colony stimulating factor and RANKL were essential to trigger and sustain osteoclastogenesis in controls. Furthermore, in 21-OHD patients, we identified a significant percentage of CD11b-CD51/CD61 and CD51/61-RANK-positive cells, which are OCPs strongly committed. Additionally, we demonstrated a T cell-dependent osteoclastogenesis from 21-OHD patients' PBMCs. T cells from patients expressed high levels of RANKL and low levels of osteoprotegerin (OPG) with respect to controls. Moreover, 21-OHD patients had higher soluble RANKL and lower OPG serum levels compared with controls; thus, soluble RANKL to OPG ratio was significantly higher in patients than controls.

CONCLUSIONS

The present study showed for the first time a high osteoclastogenic potential of PBMCs from 21-OHD patients on cGC therapy. This spontaneous osteoclastogenesis seems to be supported by both the presence of circulating OCPs and factors released by T cells.