Amplification of MDM2 has been described in a variety of human cancers. Prognostic studies have revealed that abnormal MDM2 expression correlates with poor prognosis. Many of the consequences of mdm2/p53 interactions have been investigated, and mdm2-p53 dependent events characterized. In contrast, understanding of mdm2-p53 independent activities is comparatively in it's infancy amongst these the ability of mdm2 to bind RNA. However, although the significance of this activity has been the subject of some speculation, the precise role and impact of this function upon cell replication or apoptosis has yet to be fully defined. These studies have been obstructed by a lack of specific reagents able to interfere with this reaction. As a prelude to further exploring the significance of mdm2 RNA binding we report the inhibition of mdm2 RNA binding activity by newly produced MDM2 monoclonal antibodies anti-h-mdm2 F4-14 and F2-2. A variety of MDM2 specific antibodies have been produced and applied in research without complete knowledge of their reactivity profiles, but in the face of the growing number of mdm2 RNA isoforms, the results of such studies can be difficult to interpret. Each of the RNA binding inhibitory antibodies produced in this study was found to be reactive with full length MDM2 protein expressed in tumor cell lysates, transfected NIH3T3 cell lysates and via eukaryotic cell free rabbit reticulocyte in vitro translation. Antibody F4-14, the most potently inhibitory antibody, reacts strongly with the full length MDM2 together with protein isoforms A, B, C and D. In contrast, antibody F2-2 reacts only with full-length MDM2 protein. The ability of h-mdm2-F4-14 and to a lesser extent F2-2 to inhibit RNA binding presents the possibility of modulating human mdm2s ability to bind RNA, compromise this function and present opportunities to investigate in more detail the biological significance of this activity.

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