TAT and Kaposi's sarcoma: The synergistic effects of HIV Tat and KSHV in modulating KS formation that have been identified include the following: (i) increasing KSHV infectivity in endothelial cells (21); (ii) increasing the expression (22), signaling activity (23, 24), and tumorigenicity (24) of vGPCR; (iii) promoting viral interleukin-6 (vIL-6)-induced angiogenesis and tumorigenesis (25); and (iv) enhancing K1-induced cell proliferation and angiogenesis (26).