Modeling Acute Promyelocytic Leukemia in the Mouse: New Insights in the Pathogenesis of Human Leukemias

Characteristics of Prognostic Programmed Cell Death-Related Long Noncoding RNAs Associated With Immune Infiltration and Therapeutic Responses to Colon Cancer

Programmed cell death (PCD) plays an important role in the onset and progression of various cancers. The molecular events surrounding the occurrence of abnormally expressed long noncoding RNAs (lncRNAs) leading to colon cancer (CC) have become a focus. We comprehensively evaluated the roles of PCD-related lncRNAs in the clinical management of CC and their immune responses. Therefore, we screened 41 prognostic PCD-related lncRNAs in The Cancer Genome Atlas database using co-expression analysis and assigned patients to groups according to the results of cluster analysis. The immune response and functions of cluster 2 were substantially suppressed, which might explain the poor prognosis in this group. A prognostic model comprising eight PCD-related lncRNAs was developed, and its effectiveness was verified using an external database. High-and low-risk groups had different epigenetic modifications and changes in immune cell infiltration. Patients in the high-risk group were resistant to immunotherapy and various chemotherapeutic drugs. Studies in vitro and in vivo further confirmed a carcinogenic role of the lncRNA U62317.4. Our findings of the prognostic value of PCD-related lncRNAs revealed their important roles in immune response disorders, thus providing valuable insights into the clinical management and molecular mechanisms of CC.

Retinoic Acid Receptors in Acute Myeloid Leukemia Therapy

Retinoic acid (RA) signaling pathways regulate fundamental biological processes, such as cell proliferation, development, differentiation, and apoptosis. Retinoid receptors (RARs and RXRs) are ligand-dependent transcription factors. All-trans retinoic acid (ATRA) is the principal endogenous ligand for the retinoic acid receptor alpha (RARA) and is produced by the enzymatic oxidation of dietary vitamin A, whose deficiency is associated with several pathological conditions. Differentiation therapy using ATRA revolutionized the outcome of acute promyelocytic leukemia (APL), although attempts to replicate these results in other cancer types have been met with more modest results. A better knowledge of RA signaling in different leukemia contexts is required to improve initial designs. Here, we will review the RA signaling pathway in normal and malignant hematopoiesis, and will discuss the advantages and the limitations related to retinoid therapy in acute myeloid leukemia.

HIF-2α, acting via miR-191, is involved in angiogenesis and metastasis of arsenite-transformed HBE cells

Arsenic is a well established human carcinogen that causes diseases of the lung. Some studies have suggested that hypoxia-inducible factors (HIFs) and microRNAs (miRNAs) are involved in human lung cancer; however, their molecular mechanisms that causally contribute to arsenite-caused malignant transformation of cells remain unclear. To elucidate the mechanisms of angiogenesis and metastasis of lung cancer caused by arsenite, we investigated the role of HIF-2α regulation of miRNA-191 (miR-191) in the angiogenic and metastatic properties of human bronchial epithelial (HBE) cells transformed by arsenite. In HBE cells, HIF-2α binds to the hypoxia response element (HRE) in the promoter region of miR-191 and initiates transcription of miR-191. Blocking of HIF-2α with siRNA inhibited the up-regulation of miR-191, Wilms' tumor 1 (WT1) protein, matrix metalloproteinase 9 (MMP-9), vascular endothelial growth factor (VEGF), and the down-regulation of brain acid-soluble protein 1 (BASP1). In arsenite-transformed HBE (T-HBE) cells, down-regulation of HIF-2α by siRNA blocked the process of angiogenesis and decreased their neoplastic properties and metastatic capacity, which were reversed by over-expression of miR-191 or by up-regulating WT1. Thus, HIF-2α up-regulates WT1 via miR-191, both of which are involved in the angiogenesis and metastasis of T-HBE cells. The results present a better understanding of the processes involved in lung cancer caused by arsenite exposure.

P38 MAP kinase functions as a switch in MS-275-induced reactive oxygen species-dependent autophagy and apoptosis in human colon cancer cells

MS-275 is a synthetic benzamide derivative of the histone deacetylase inhibitor and is currently in phase I/II clinical trials. Many reports have shown that the anti-tumor activity of MS-275 in several types of cancer is mainly attributable to its capacity to induce the apoptotic death of tumor cells. It remains unclear if autophagy is involved in MS-275 treatment of cancer cells. Here, we first show that MS-275 induces human colon cancer cell HCT116 autophagy as well as apoptosis. Short-term treatment (24h) induced HCT116 cells to undergo autophagy with dependence on intracellular reactive oxygen species production and ERK activation. The activated reactive oxygen species/ERK signal promoted Atg7 protein expression, which triggered MS-275-induced cancer cell autophagy. However, after prolonged treatment with MS-275 (over 48h), autophagic cells turned apoptotic, which was also dependent on reactive oxygen species generation. Interestingly, we found that p38 MAP kinase played a vital role in the switch from autophagy to apoptosis in MS-275-induced human colon cancer cells. High expression of p38 induced cell autophagy, but low expression resulted in apoptosis. In addition, observations in vivo are strongly consistent with the in vitro results. Therefore, these findings extend our understanding of the action of MS-275 in inducing cancer cell death and suggest that it may be a promising clinical chemotherapeutic agent with multiple effects.

Microarray analysis of oxidative stress regulated genes in mesencephalic dopaminergic neuronal cells: relevance to oxidative damage in Parkinson's disease

Oxidative stress and apoptotic cell death have been implicated in the dopaminergic cell loss that characterizes Parkinson's disease. While factors contributing to apoptotic cell death are not well characterized, oxidative stress is known to activate an array of cell signaling molecules that participate in apoptotic cell death mechanisms. We investigated oxidative stress-induced cytotoxicity of hydrogen peroxide (H2O2) in three cell lines, the dopaminergic mesencephalon-derived N27 cell line, the GABAergic striatum-derived M213-20 cell line, and the hippocampal HN2-5 cell line. N27 cells were more sensitive to H2O2-induced cell death than M213-20 and HN2-5 cells. H2O2 induced significantly greater increases in caspase-3 activity in N27 cells than in M213-20 cells. H2O2-induced apoptotic cell death in N27 cells was mediated by caspase-3-dependent proteolytic activation of PKCdelta. Gene expression microarrays were employed to examine the specific transcriptional changes in N27 cells exposed to 100 microM H2O2 for 4 h. Changes in genes encoding pro- or anti-apoptotic proteins included up-regulation of BIK, PAWR, STAT5B, NPAS2, Jun B, MEK4, CCT7, PPP3CC, and PSDM3, while key down-regulated genes included BNIP3, NPTXR, RAGA, STK6, YWHAH, and MAP2K1. Overall, the changes indicate a modulation of transcriptional activity, chaperone activity, kinase activity, and apoptotic activity that appears highly specific, coordinated and relevant to cell survival. Utilizing this in vitro model to identify novel oxidative stress-regulated genes may be useful in unraveling the molecular mechanisms underlying dopaminergic degeneration in Parkinson's disease.

High-penetrance mouse model of acute promyelocytic leukemia with very low levels of PML-RARalpha expression

Transgenic mice expressing PML-RARalpha in early myeloid cells under control of human cathepsin G regulatory sequences all develop a myeloproliferative syndrome, but only 15% to 20% develop acute promyelocytic leukemia (APL) after a latent period of 6 to 14 months. However, this transgene is expressed at very low levels in the bone marrow cells of transgenic mice. Because the transgene includes only 6 kb of regulatory sequences from the human cathepsin G locus, we hypothesized that sequences required for high-level expression of the transgene might be located elsewhere in the cathepsin G locus and that a knock-in model might yield much higher expression levels and higher penetrance of disease. We, therefore, targeted a human PML-RARalpha cDNA to the 5' untranslated region of the murine cathepsin G gene, using homologous recombination in embryonic stem cells. This model produced a high-penetrance APL phenotype, with more than 90% of knock-in mice developing APL between 6 and 16 months of age. The latent period and phenotype of APL (including a low frequency of an interstitial deletion of chromosome 2) was similar to that of the previous transgenic model. Remarkably, however, the expression level of PML-RARalpha in bone marrow cells or APL cells was less than 3% of that measured in the low-penetrance transgenic model. Although the explanation for this result is not yet clear, one hypothesis suggests that very low levels of PML-RARalpha expression in early myeloid cells may be optimal for the development of APL in mice.

How acute promyelocytic leukaemia revived arsenic

Despite its many therapeutic qualities, arsenic trioxide has been more commonly remembered as Madame Bovary's poison than as an anticancer drug. The ability of arsenic trioxide to treat acute promyelocytic leukaemia has radically changed this view, providing new insights into the pathogenesis of this malignancy and raising hopes that arsenicals might be useful in treating other cancers.

Altered myelopoiesis and the development of acute myeloid leukemia in transgenic mice overexpressing cyclin A1

A mammalian A-type cyclin, cyclin A1, is highly expressed in testes of both human and mouse and targeted mutagenesis in the mouse has revealed the unique requirement for cyclin A1 in the progression of male germ cells through the meiotic cell cycle. While very low levels of cyclin A1 have been reported in the human hematopoietic system and brain, the sites of elevated levels of expression of human cyclin A1 were several leukemia cell lines and blood samples from patients with hematopoietic malignances, notably acute myeloid leukemia. To evaluate whether cyclin A1 is directly involved with the development of myeloid leukemia, mouse cyclin A1 protein was overexpressed in the myeloid lineage of transgenic mice under the direction of the human cathepsin G (hCG) promoter. The resulting transgenic mice exhibited an increased proportion of immature myeloid cells in the peripheral blood, bone marrow, and spleen. The abnormal myelopoiesis developed within the first few months after birth and progressed to overt acute myeloid leukemia at a low frequency ( approximately 15%) over the course of 7-14 months. Both the abnormalities in myelopoiesis and the leukemic state could be transplanted to irradiated SCID (severe combined immunodeficient) mice. The observations suggest that cyclin A1 overexpression results in abnormal myelopoiesis and is necessary, but not sufficient in the cooperative events inducing the transformed phenotype. The data further support an important role of cyclin A1 in hematopoiesis and the etiology of myeloid leukemia.