Cyclic AMP, beta-1 integrins, and human T-cell leukemia virus type 1-associated syncytium formation: Cellular effectors of pathology

Human T-cell leukemia virus type 1 (HTLV-1) is associated with a spectrum of pathologies, including HTLV-1-associated myelopathy, which are characterized by extensive inflammation and tissue lesions. In vitro, the HTLV-1-immortalized MT-2 cell line forms polynuclear syncytia when mixed with susceptible uninfected cells. This fusion is independent of viral transmission or productive infection. This thesis examines the causes of cellular susceptibility to HTLV-1-associated fusion, and the roles of cellular adhesion molecules and signaling pathways in this process.; Results in our laboratory indicate that K562 cells lose their immunity to HTLV-1 mediated fusion when they are made to express VCAM-1 (KVCAM cells) (Hildreth et al. 1997). Increasing cyclic AMP (cAMP) levels or activating adenylate cyclase with forskolin were found to increase the average number of syncytia between MT-2 and KVCAM cells by 70% (p = 0.000) or 85% (p = 0.000), respectively. Inhibition of adenylate cyclase with 2'3 '-dideoxyadenosine (23DOA) reduced HTLV-1 syncytium formation by 54% (p = 0.000). Modulation of fusion is not due to changes in viral protein expression or adhesion molecule expression, although fusion did require de novo protein synthesis. Inhibition of adenylate cyclase by 23DOA in KVCAM cells resulted in a reduction of colocalization between VCAM-1 and GM-1 to levels seen on nonfusogenic PM-1 cells. These results suggest that VCAM-1 requires appropriate lipid context to confer susceptibility to HTLV-1-mediated fusion, and that adenylate cyclase activity is essential to maintaining that context in KVCAM cells.; The association of VCAM-1 expression and susceptibility to HTLV-1-mediated fusion in KVCAM cells suggests that the VCAM-1 counter-receptor beta1 integrin may also have a role in HTLV-1-mediated fusion. beta1 integrin cross-linking agents were tested for their ability to modulate fusion. The anti-CD29 mAb 4B4 blocked adhesion of MT-2 cells to VCAM-1, but also enhanced HTLV-1 syncytium formation by 88% (p = 0.027). Fibronectin substrate enhanced fusion by 49% (p = 0.035), but enhancement was reversed by 4134, indicating that beta1 integrin cross-linking, rather than 1:1 integrin-ligand binding, is associated with enhancement of HTLV-1-mediated fusion.; Together, these results suggest significant roles for adenylate cyclase and beta1 integrin-associated signaling in HTLV-1 pathogenesis.