Reactivity of anti-proliferating cell nuclear antigen (PCNA) murine monoclonal antibodies and human autoantibodies to the PCNA multiprotein complexesinvolved in cell proliferation

Proliferating cell nuclear Ag (PCNA) occurs as a component of multiprotein complexes during cell proliferation. We found the complexes to react with m urine anti-PCNA mAbs, but not with anti-PCNA Abs in lupus sera. The complex es were purified from rabbit thymus extract by affinity chromatography usin g anti-PCNA mAbs (TOB7, TO17, and TO30) and analyzed by ELISA, immunoprecip itation, immunoblotting, and HPLC gel filtration. That PCNA was complexed w ith other proteins was demonstrated by its copurification with a group of p roteins excluded by an HPLC G3000 SW column. Although immunoblot analysis s howed the mAbs to react exclusively with the 34-kDa PCNA polypeptide, they nonetheless immunoprecipitated the same group of proteins, confirming the i nteraction of the isolated PCNA with other proteins. Anti-PCNA sera, includ ing AK, which reacts with biologically functional sites on PCNA, did not re act with complexed PCNA, but did react with it once it was dissociated from the complexes. PCNA complexes in turn reacted with murine anti-DNA mAbs, a s well as with Abs against p21, replication protein A, DNA helicase Il, cyc lin-dependent kinases 4 and 5, and topoisomerase I. These findings suggest that the PCNA complexes purified using anti-PCNA mAbs comprise the "protein machinery" for DNA replication and cell cycle regulation. They also sugges t that anti-PCNA mAbs are useful tools with which to characterize the prote in-protein interactions within PCNA complexes, as wen as the autoimmune res ponses to proteins interacting with PCNA, which may shed light on the mecha nisms of autoantibody production in lupus patients.