Furthermore, the HIV-1 Tat protein acts as a tumor-promoting cofactor: secreted within KS lesions, Tat stimulates proliferation, migration, and invasion of tumor-derived endothelial cells, synergizing with HHV-8 vGPCR to activate the NF-AT and NF-κB pathways. The gene discussed is NFKB1; the disease is Kaposi's sarcoma.