A tumor necrosis factor alpha- and interleukin 6-inducible protein that interacts with the small subunit of DNA polymerase delta and proliferating cell nuclear antigen

A cDNA encoding a protein of 36 kDa, polymerase delta-interacting protein 1 (PDIP1), that interacts with the small subunit (p50) of DNA polymerase del ta (pol delta) was identified in a two-hybrid screen of a HepG2 cDNA librar y by using p50 as bait. The interaction of PDIP1 with p50 was confirmed by pull-down assays, and a similar assay was used to demonstrate that PDIP1 in teracts directly with the proliferating cell nuclear antigen (PCNA). PCNA a nd p50 bound to PDIP1 simultaneously, and PDIP1 stimulated pol delta activi ty in vitro in the presence, but not the absence, of PCNA, suggesting that PDIP1 also interacts functionally with both p50 and PCNA. Subcellular local ization studies demonstrated that PDIP1 is a nuclear protein that colocaliz es with PCNA at replication foci. A putative PCNA-binding motif was identif ied within the C terminus of PDIP1, and a synthetic peptide containing this PCNA-binding motif was shown to bind PCNA by far-Western analysis. Norther n analysis demonstrated that PDIP1 rnRNA is present in a wide variety of hu man tissues. PDIP1 was found to be highly homologous to a previously identi fied protein, B12 [Wolf, F. W., Marks, R. M., Sarma. V., Byers, M. G., Katz , R. W., Shows, T. B. & Dixit, V. M. (1992) J. BioL Chem. 267,1317-1326], o ne of the early response genes induced by tumor necrosis factor alpha. PDIP 1 synthesis can also be induced by tumor necrosis factor alpha and by IL-6, cytokines essential for liver regeneration after loss of hepatic tissue. I t is suggested that PDIP1 provides a link between cytokine activation and D NA replication in liver as well as in other tissues.