Coronaviruses assemble and obtain their envelope at membranes of the intermediate compartment between the endoplasmic reticulum and Golgi complex. Like other enveloped viruses, coronavirus assembly is presumably dependent on protein localization and protein-protein as well as protein-RNA interactions. We have used the bovine coronavirus (BCV) as a model to study interactions between the viral proteins in virus-infected cells that are important for coronavirus assembly. BCV is a prototype for the coronaviruses that express an additional major structural protein, the hemagglutinin esterase (HE), in addition to the spike(S) glycoprotein, membrane (M) glycoprotein, and nucleocapsid (N) protein. Complexes consisting of the M, S, and HE proteins were detected in virus-infected cells by coimmunoprecipitations. Kinetic analyses demonstrated that S protein and HE each quickly formed a complex with M protein after synthesis, whereas heterocomplexes consisting of all three proteins formed more slowly. The kinetics of HE biosynthesis revealed that the half-life of oligomerization was ϳ30 min, which correlated with the appearance of complexes consisting of M, HE, and S proteins, suggesting that oligomerization and/or conformational changes may be important for the S-M-HE protein complexes to form. Only HE dimers were found associated with the heterocomplexes consisting of all three proteins. S-M-HE protein complexes were detected prior to processing of the oligosaccharide chains on HE, indicating that these protein complexes formed in a premedial Golgi compartment before trimming of sugar chains. Transient coexpressions and double-labeling immunofluorescence demonstrated that HE and S proteins colocalized with M protein. This was further supported by coimmunoprecipitation of specific HE-M and S-M protein complexes from transfected cells, indicating that these proteins can form complexes in the absence of other viral proteins.

Interestingly, the addition of an anti-IL-2R-␣ monoclonal antibody profoundly inhibited IL-9 expression, suggesting optimal expression of IL-9 was dependent on IL-2 signaling in these patients. To determine whether there would be autonomous proliferation of ATL leukemic cells, we purified leukemic cells from patients with smoldering/chronic ATL. Purified leukemic cells cultured alone produced IL-2/ IL-9, and the downstream Janus kinase/ signal transducer and activator of transcription pathway was activated. However, the leukemic cells did not proliferate independently, but required coculture with autologous monocytes to induce proliferation. Moreover, interaction between leukemic cells and monocytes was contact dependent, and major histocompatibility complex class II expression may have contributed to this interaction. In conclusion, our data provide evidence that there is autocrine/paracrine cytokine stimulation of leukemic cell proliferation in patients with smoldering/chronic ATL that could be targeted for treatment. IntroductionAdult T-cell leukemia (ATL) that is caused by human T-cell lymphotropic virus I (HTLV-1) is an aggressive malignancy of CD4-and CD25-expressing leukemia, and lymphoma cells. ATL is a heterogeneous disease that can be divided broadly into 4 stages: smoldering, chronic, lymphoma, and acute-type ATL. The common clinical manifestations of ATL are skin lesions, hypercalcemia, immunologic anergy to antigen stimulation, and cells with "flowerlike" nuclei in the circulation. Smoldering/chronic ATL patients have normal or mildly increased white blood cell counts with a variable number of leukemic cells in the circulation and are generally associated with a better prognosis. Patients with acutetype ATL have organ dysfunction associated with circulating leukemic cells and are generally associated with a poor prognosis. The mechanisms underlying the progression from smoldering/chronic stage to the acute stage are unknown; however, the accumulation of molecular mutations is thought to play a role in this progression.Although the pathogenesis of ATL is unknown, the virally encoded regulatory protein, HTLV-1 Tax, seems to play a central role in the initial leukemogenesis of ATL. Hasegawa et al demonstrated that overexpression of Tax in immature thymocytes induced leukemia/lymphoma in mice with clinical, pathologic, and immunologic features characteristic of ATL after a long latency. 1 Subsequently, Ohsugi et al 2 showed that Tax is able to promote oncogenesis not only with immature T cells, but also with mature T cells. Both experiments highlighted the importance of Tax in the initial development of ATL.Beyond the in vivo mouse models, numerous in vitro studies have demonstrated the essential role of Tax in ATL initiation and shed light on the mechanism of Tax-mediated cellular transformation. 3 Tax deregulates the expression of genes involved in cellular proliferation, cell-cycle control, and apoptosis through physical interaction with cellular elements, including transcription factors such as nuc...

The etiologic agent of adult T-cell leukemia (ATL) is human T cell lymphotropic virus type I (HTLV-I). The HTLV-I proteinTax alters gene expression, including those of cytokines and their receptors, which plays an important role in early stages of ATL. Here we demonstrate that expression of interleukin-9 (IL-9) is activated by Tax via an NF-B motif in its proximal promoter, whereas IL-9 receptor-␣ (IL-9R␣) expression is not induced by Tax. However, supporting a role for IL-9/IL-9R␣ in ATL, a neutralizing monoclonal antibody directed toward IL-9R␣ inhibited ex vivo spontaneous proliferation of primary ATL cells from several patients. Fluorescence-activated cell sorter analysis of freshly isolated peripheral blood mononuclear cells from these patients revealed high level expression of IL-9R␣ on their CD14-expressing monocytes. Furthermore, purified T cells or monocytes alone from these patients did not proliferate ex vivo, whereas mixtures of these cell types manifested significant proliferation through a contact-dependent manner. Taken together, our data suggest that primary ATL cells, via IL-9, support the action of IL-9R␣/CD14-expressing monocytes, which subsequently support the ex vivo spontaneous proliferation of malignant T cells. In summary, these data support a role for IL-9 and its receptor in ATL by a paracrine mechanism. (Blood. 2008; 111:5163-5172) IntroductionAdult T-cell leukemia (ATL) is a highly aggressive neoplasm characterized by a clonal expansion of CD4 ϩ lymphocytes and by a monoclonal integration of human T cell lymphotropic virus type I (HTLV-I) provirus(es) in the tumor cells. 1,2 HTLV-I is a type C retrovirus endemic in southern Japan, the Caribbean basin, Central and Southern Africa, and South America. 3,4 Less than 5% of HTLV-I-infected persons develop either ATL or a chronic inflammatory disease of the central nervous system termed HTLV-Iassociated myelopathy/tropical spastic paraparesis (HAM/TSP). Although the precise mechanisms of ATL leukemogenesis remain unclear, it has been suggested that the transformation of T cells in the early stages of the disease is mediated by the HTLV-I Tax protein (p40). Tax activates long terminal repeat-directed transcription by recruiting members of the cAMP response element-binding/ and activating transcription factors family to the viral promoter. In addition, Tax activates other cellular transcription factors, such as NF-B. Tax is associated with the expression of cellular genes, 5 including the cytokine 6-10 and cytokine receptor genes. 7,[11][12][13] It has been suggested that the dysregulation of cytokines and their receptors in HTLV-I-infected persons may play an important role in the early course of disease via autocrine stimulation. 9,11 Interleukin-9 (IL-9) is a T cell-derived cytokine with pleiotropic activities on various cell types. 14-16 IL-9 is mainly expressed by activated CD4 ϩ T cells. 17 The functions of IL-9 are mediated through the IL-9 receptor (IL-9R), which is a member of the hematopoietin receptor superfamily. 18 The IL-9 recept...