Polyomavirus causes a broad spectrum of tumors. Because it requires cellular S phase to replicate, polyoma has evolved diverse mechanisms by which transforming gene products (T antigens) promote cell cycle progression. Since these mechanisms target normal cell components of growth control, information gained here is generally relevant to the problem of neoplasia. This work involves aspects of each of the 3 transforming gene products. An N-terminal J domain common all 3 T antigens connects them to chaperone systems. J function is clearly different for different T antigens. LT regulates Rb tumor suppressors by both J dependent and J independent mechanisms; experiments will determine the range of Rb family functions that LT affects by each mechanism. Sequences in Rb required for J inactivation will be determined. Experiments on p130, an Rb family member associated with cell cycle withdrawal will determine the basis for, and consequences of LT induced phosphorylation. We will probe the structure and function of J domains in large T(LT) and small T(ST) to differentiate sequences required for large T(LT) regulation of tumor suppressors of the retinoblastoma susceptibility (Rb) gene family from those connected to small T(ST) regulation of protein phosphatase 2A(PP2A). The contributions of the J domain structure to virus replication will be dissected. Cellular J domains will be tested to determine whether they regulate normal cellular gene expression. Novel functions in LT that regulate cell growth and gene expression will be mapped, and their cellular targets determined. Large T phosphorylation sites will be determined and tested to determine whether they regulate interactions with the tumor suppressors. Middle T (MT) is critical for tumor induction. Novel sites of tyrosine phosphorylation will be mapped and their function tested by mutation. The cellular proteins interacting with those sites will be determined. Since the ability of MT to cause tumors and to promote cell survival is strongly connected to interaction with phosphatidylinositol 3-kinase (PI3K), the connection between MT function and PDK1, a newly discovered initial target of inositol phospholipids, will be examined.
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