Severe acute respiratory syndrome coronavirus (SARS-CoV) causes a lung disease with high mortality. In addition, osteonecrosis and bone abnormalities with reduced bone density have been observed in patients following recovery from SARS, which were partly but not entirely explained by the short-term use of steroids. Here, we demonstrate that human monocytes, potential precursors of osteoclasts, partly express angiotensin converting enzyme 2 (ACE2), a cellular receptor of SARS-CoV, and that expression of an accessory protein of SARS-CoV, 3a/X1, in murine macrophage cell line RAW264.7 cells, enhanced NF-kappaB activity and differentiation into osteoclast-like cells in the presence of receptor activator of NF-kappaB ligand (RANKL). Furthermore, human epithelial A549 cells expressed ACE2, and expression of 3a/X1 in these cells up-regulated TNF-alpha, which is known to accelerate osteoclastogenesis. 3a/X1 also enhanced RANKL expression in mouse stromal ST2 cells. These findings indicate that SARS-CoV 3a/X1 might promote osteoclastogenesis by direct and indirect mechanisms.

Neutrophils, basophils, and monocytes are continuously produced in bone marrow via myelopoiesis, circulate in blood, and are eventually removed from circulation to maintain homeostasis. To quantitate the kinetics of myeloid cell movement during homeostasis, we applied 5-bromo-2'-deoxyuridine pulse labeling in healthy rhesus macaques () followed by hematology and flow cytometry analyses. Results were applied to a mathematical model, and the blood circulating half-life and daily production, respectively, of each cell type from macaques aged 5-10 y old were calculated for neutrophils (1.63 ± 0.16 d, 1.42 × 10 cells/l/d), basophils (1.78 ± 0.30 d, 5.89 × 10 cells/l/d), and CD14CD16 classical monocytes (1.01 ± 0.15 d, 3.09 × 10 cells/l/d). Classical monocytes were released into the blood circulation as early as 1 d after dividing, whereas neutrophils remained in bone marrow 4-5 d before being released. Among granulocytes, neutrophils and basophils exhibited distinct kinetics in bone marrow maturation time and blood circulation. With increasing chronological age, there was a significant decrease in daily production of neutrophils and basophils, but the half-life of these granulocytes remained unchanged between 3 and 19 y of age. In contrast, daily production of classical monocytes remained stable through 19 y of age but exhibited a significant decline in half-life. These results demonstrated relatively short half-lives and continuous replenishment of neutrophils, basophils, and classical monocytes during homeostasis in adult rhesus macaques with compensations observed during increasing chronological age.

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Expression of human T-cell leukemia virus type-1 (HTLV-1) in adult T-cell leukemia (ATL) cells is known to be marginal in vivo and inducible in short-term culture. In this study, we demonstrated that withdrawal of interleukin (IL)-2 from IL-2-dependent ATL cell lines resulted in induction of HTLV-1 mRNA and protein expression, and that viral induction was associated with phosphorylation of the stress kinase p38 and its downstream CREB. Pharmacological inhibitors of the p38 pathway suppressed viral expression induced by IL-2 depletion. These results indicate that the stress-induced p38 pathway might up-regulate HTLV-1 gene expression through at least CREB activation.

Infection of erythroid cells by Friend spleen focus-forming virus (SFFV) leads to acute erythroid hyperplasia in mice due to expression of its unique envelope glycoprotein, gp55. Erythroid cells expressing SFFV gp55 proliferate in the absence of their normal regulator, erythropoietin (Epo), because of interaction of the viral envelope protein with the erythropoietin receptor and a short form of the receptor tyrosine kinase Stk (sf-Stk), leading to constitutive activation of several signal transduction pathways. Our previous in vitro studies showed that phosphatidylinositol 3-kinase (PI3-kinase) is activated in SFFV-infected cells and is important in mediating the biological effects of the virus. To determine the role of PI3-kinase in SFFV-induced disease, mice deficient in the p85␣ regulatory subunit of class IA PI3-kinase were inoculated with different strains of SFFV. We observed that p85␣ status determined the extent of erythroid hyperplasia induced by the sf-Stk-dependent viruses SFFV-P (polycythemia-inducing strain of SFFV) and SFFV-A (anemia-inducing strain of SFFV) but not by the sf-Stk-independent SFFV variant BB6. Our data also indicate that p85␣ status determines the response of mice to stress erythropoiesis, consistent with a previous report showing that SFFV uses a stress erythropoiesis pathway to induce erythroleukemia. We further showed that sf-Stk interacts with p85␣ and that this interaction depends upon sf-Stk kinase activity and tyrosine 436 in the multifunctional docking site. Pharmacological inhibition of PI3-kinase blocked proliferation of primary erythroleukemia cells from SFFV-infected mice and the erythroleukemia cell lines derived from them. These results indicate that p85␣ may regulate sf-Stk-dependent erythroid proliferation induced by SFFV as well as stress-induced erythroid hyperplasia.The Friend spleen focus-forming virus (SFFV) is a highly pathogenic retrovirus that induces rapid erythroblastosis in susceptible strains of mice (for a review, see reference 42). Friend SFFV is a replication-defective virus with deletions in its env gene, giving rise to a unique glycoprotein, SFFV gp55. This unique glycoprotein confers pathogenicity to the virus; a vector encoding SFFV gp55 alone is sufficient to induce erythroblastosis in susceptible strains of mice (49). The Fv-2 gene encodes one of the key susceptibility factors for SFFV-induced erythroid disease (18, 37), as follows: the receptor tyrosine kinase Stk/RON, a member of the Met family of receptor tyrosine kinases (11-12). Susceptibility to SFFV-induced disease is associated with expression of a short form of the receptor tyrosine kinase Stk, termed sf-Stk, that is transcribed from an internal promoter within the Stk gene of Fv-2-susceptible (Fv-2 ss ) mice but not Fv-2-resistant (Fv-2 rr ) mice (37) and is abundantly expressed in erythroid cells (11). Infection of erythroid cells with the polycythemia-inducing strain of SFFV (SFFV-P) induces erythropoietin (Epo)-independent proliferation and differentiation, whereas erythroid cells in...