Kaposi's sarcoma (KS)-associated herpesvirus (KSHV; also called human herpesvirus 8) is believed to be the etiologic agent of Kaposi's sarcoma, multicentric Castleman's disease, and AIDS-associated primary effusion lymphoma. KSHV infection of human dermal microvascular endothelial cells (DMVEC) in culture results in the conversion of cobblestone-shaped cells to spindle-shaped cells, a characteristic morphological feature of cells in KS lesions. All spindle-shaped cells in KSHV-infected DMVEC cultures express the latency-associated nuclear protein LANA1, and a subfraction of these cells undergo spontaneous lytic cycle induction that can be enhanced by tetradecanoyl phorbol acetate (TPA) treatment. To study the cellular response to infection by KSHV, we used two different gene array screening systems to examine the expression profile of either 2,350 or 9,180 human genes in infected compared to uninfected DMVEC cultures in both the presence and absence of TPA. In both cases, between 1.4 and 2.5% of the genes tested were found to be significantly upregulated or downregulated. Further analysis by both standard and real-time reverse transcription-PCR procedures directly confirmed these results for 14 of the most highly upregulated and 13 of the most highly downregulated genes out of a total of 37 that were selected for testing. These included strong upregulation of interferon-responsive genes such as interferon response factor 7 (IRF7) and myxovirus resistance protein R1, plus upregulation of exodus 2 beta-chemokine, RDC1 alpha-chemokine receptor, and transforming growth factor beta3, together with strong downregulation of cell adhesion factors alpha(4)-integrin and fibronectin plus downregulation of bone morphogenesis protein 4, matrix metalloproteinase 2, endothelial plasminogen activator inhibitor 1, connective tissue growth factor, and interleukin-8. Significant dysregulation of several other cytokine-related genes or receptors, as well as endothelial cell and macrophage markers, and various other genes associated with angiogenesis or transformation was also detected. Western immunoblot and immunohistochemical analyses confirmed that the cellular IRF7 protein levels were strongly upregulated during the early lytic cycle both in KSHV-infected DMVEC and in the body cavity-based lymphoma BCBL1 PEL cell line.