ID1 and Kaposi's sarcoma: LANA up-regulated Id expression through constitutively sustaining the activation of the BMP-Smad1-Id signaling pathway, and thus contributed to the oncogenicity of KMM cells in vitro and in vivo. These studies have identified a novel viral oncogenic signaling pathway, and our data indicate that small inhibitors targeting BMP-Smad1-Id signaling pathway could be promising candidates for the treatment of KS.