The Pur protein family: clues to function from recent studies on cancer and AIDS.

The Pur protein family consists of four known members in humans, the prototype gene for which is strongly conserved throughout evolution. Several investigations have now implicated Pur alpha in pathways of inhibition of oncogenic transformation. Clues to the potential importance of Pur family members in cancer are derived from observations of genetic alterations of both Pur alpha and Pur beta in myelodysplastic syndrome progressing to acute myelogenous leukemia. A role for newly-discovered Pur gamma in neoplasia is also beginning to emerge as studies have indicated that cellular levels of two Pur gamma isoforms are elevated in certain tumors. A variety of studies have now implicated Pur alpha in development of blood cells and cells of the central nervous system. Clues to the functions of Pur alpha, a key family member, have recently been derived from studies of the interactions of HIV-1 and JC virus (JCV) in AIDS. JCV causes an opportunistic infection in the brains of certain HIV-1-infected individuals. Pur alpha can influence this viral interaction through functional associations with the Tat protein and TAR RNA of HIV-1, and with large T-antigen and DNA regulatory regions of JCV. Evidence is now strong that Pur alpha interacts with both DNA and RNA and that an important aspect of its function is to recruit regulatory proteins to specific nucleic acid sequences in processes as diverse as DNA replication, gene transcription, RNA transport in the cytoplasm and compartmentalized mRNA translation.