Kaposi's sarcoma (KS) is the major neoplastic manifestation of AIDS. Prior data indicate that KS spindle cell growth and spread can be driven by cytokines like IL-6, oncostatin M, VEGF and bFGF as well as the HIV gene product TAT. HIV-1 TAT can bind to the FLK-1/KDR receptor for the vascular endothelial growth factor (VEGF), and contains a classical RGD sequence which may activate surface integrin receptors for fibronectin and vitronectin. Furthermore, the Kaposi's sarcoma herpes virus (KSHV)/human herpes virus type 8 (HHV-8) appears to be a """"""""molecular pirate"""""""" whose open reading frames encode homologs of IL-6, the chemokine MIP1 and an activated IL-8 chemokine receptor. Despite extensive studies on modulation of KS cell growth by these soluble mediators, relatively little is known about their signal transduction pathways. To that end, we have begun to characterize cytokine, chemokine and TAT signaling pathways in a permanent KS spindle cell line with authentic properties of primary cells. We observed that the related adhesion focal tyrosine kinase (RAFTK), a newly discovered signaling molecule, prominently participates in all three pathways, and transmits signals to the transcriptional apparatus and the cytoskeleton. Our overall aim is to characterize signal transduction pathways in KS spindle cells that mediate their growth and spread using RAFTK as a primary focus of study. We are assisted in these studies by having specific reagents against RAFTK as well as dominant-negative RAFTK mutants. We will seek first to identify the signaling molecules that associate with cytokine, chemokine and TAT surface receptors, then study how these molecules connect to RAFTK, and proceed to characterize mediators downstream of RAFTK which lead to cytoskeletal and transcriptional activation. This structured approach to characterize cytokine, chemokine and TAT signaling pathways and their functional roles in KS spindle cells should provide insight into the mechanisms of KS growth and spread.
