Importance of receptor usage, Fli1 activation, and mouse strain for the stem cell specificity of 10A1 murine leukemia virus leukemogenicity

A Novel Chalcone Derivative Regulates the Expression and Phosphorylation of ERK1/2 by Inhibiting Fli-1 Promoter Activity for Preventing the Malignant Progression of Erythroleukemia

Acute erythroleukemia is a rare form of acute myeloid leukemia recognized by its distinct phenotypic attribute of erythroblasts proliferation. In this study, in vitro experiments showed that a newly synthesized chalcone (ZH-254) inhibited cell proliferation, caused apoptosis, arrested the cell cycle in the G1 phase, and downregulated Fli-1 expression by inhibiting Fli-1 promoter activity. In vivo experiments showed that ZH-254 could effectively alleviate splenomegaly and prolong the survival of erythroleukemia mice. RT-PCR and Western blot analysis showed that ZH-254 could regulate the expression of Fli-1 target genes and G1-phase-related cell cycle proteins, including Rb, Bcl-2, Bax, ERK1/2, Gata-1, P110, SHIP-1, p-ERK1, CDK4, C-myc, Cyclin D1, Smad-3, GSK-3, and p21. Among them, the compound most significantly regulated the expression and phosphorylation of ERK1, the target gene of Fli-1 involved in regulating cell proliferation and apoptosis. Thus, ZH-254 restricts the malignancy of erythroleukemia by causing the inactivation of Fli-1 expression via suppressing its promoter activity, further regulating the expression and phosphorylation of ERK1- and G1-phase-related genes. These results reveal the critical role of Fli-1 in the growth and survival of various hematological malignancies and point to chalcone derivatives as lead compounds for the development of anti-Fli-1 drugs for the treatment of erythroleukemia with overexpression of Fli-1.

Protease-sensitive prion species in neoplastic spleens of prion-infected mice with uncoupling of PrP(Sc) and prion infectivity

Prion diseases are fatal neurodegenerative disorders. An important step in disease pathophysiology is the conversion of cellular prion protein (PrP(C)) to disease-associated misfolded conformers (PrP(Sc)). These misfolded PrP variants are a common component of prion infectivity and are detectable in diseased brain and lymphoreticular organs such as spleen. In the latter, PrP(Sc) is thought to replicate mainly in follicular dendritic cells within spleen follicles. Although the presence of PrP(Sc) is a hallmark for prion disease and serves as a main diagnostic criterion, in certain instances the amount of PrP(Sc) does not correlate well with neurotoxicity or prion infectivity. Therefore, it has been proposed that prions might be a mixture of different conformers and aggregates with differing properties. This study investigated the impact of disruption of spleen architecture by neoplasia on the abundance of different PrP species in spleens of prion-infected mice. Although follicular integrity was completely disturbed, titres of prion infectivity in neoplastic spleens were not significantly altered, yet no protease-resistant PrP(Sc) was detectable. Instead, unique protease-sensitive prion species could be detected in neoplastic spleens. These results indicate the dissociation of PrP(Sc) and prion infectivity and showed the presence of non-PrP(Sc) PrP species in spleen with divergent biochemical properties that become apparent after tissue architecture disruption.

Persistent retroviral infection with MoMuLV influences neuropathological signature and phenotype of prion disease

A fundamental step in pathophysiology of prion diseases is the conversion of the host encoded prion protein (PrP(C)) into a misfolded isoform (PrP(Sc)) that accumulates mainly in neuronal but also non-neuronal tissues. Prion diseases are transmissible within and between species. In a subset of prion diseases, peripheral prion uptake and subsequent transport to the central nervous system are key to disease initiation. The involvement of retroviruses in this process has been postulated based on the findings that retroviral infections enhance the spread of prion infectivity and PrP(Sc) from cell to cell in vitro. To study whether retroviral infection influences the phenotype of prion disease or the spread of prion infectivity and PrP(Sc) in vivo, we developed a murine model with persistent Moloney murine leukemia retrovirus (MoMuLV) infection with and without additional prion infection. We investigated the pathophysiology of prion disease in MoMuLV and prion-infected mice, monitoring temporal kinetics of PrP(Sc) spread and prion infectivity, as well as clinical presentation. Unexpectedly, infection of MoMuLV challenged mice with prions did not change incubation time to clinical prion disease. However, clinical presentation of prion disease was altered in mice infected with both pathogens. This was paralleled by remarkably enhanced astrogliosis and pathognomonic astrocyte morphology in the brain of these mice. Therefore, we conclude that persistent viral infection might act as a disease modifier in prion disease.

Homing and invasiveness of MLL/ENL leukemic cells is regulated by MEF2C

Acute myelogenous leukemia is driven by leukemic stem cells (LSCs) generated by mutations that confer (or maintain) self-renewal potential coupled to an aberrant differentiation program. Using retroviral mutagenesis, we identified genes that generate LSCs in collaboration with genetic disruption of the gene encoding interferon response factor 8 (Irf8), which induces a myeloproliferation in vivo. Among the targeted genes, we identified Mef2c, encoding a MCM1-agamous-deficiens-serum response factor transcription factor, and confirmed that overexpression induced a myelomonocytic leukemia in cooperation with Irf8 deficiency. Strikingly, several of the genes identified in our screen have been reported to be up-regulated in the mixed-lineage leukemia (MLL) subtype. High MEF2C expression levels were confirmed in acute myelogenous leukemia patient samples with MLL gene disruptions, prompting an investigation of the causal interplay. Using a conditional mouse strain, we demonstrated that Mef2c deficiency does not impair the establishment or maintenance of LSCs generated in vitro by MLL/ENL fusion proteins; however, its loss led to compromised homing and invasiveness of the tumor cells. Mef2c-dependent targets included several genes encoding matrix metalloproteinases and chemokine ligands and receptors, providing a mechanistic link to increased homing and motility. Thus, MEF2C up-regulation may be responsible for the aggressive nature of this leukemia subtype.