Identification of novel parafibromin protein partners using a proteomic approach

Authors

• PR Adikaram
• J Zhang
• M Pandey
• WF Simonds

Abstract

Parafibromin is a tumor suppressor protein encoded by the CDC73 gene. Mutations in this gene have been linked to Hyperparathyroidism-Jaw Tumor Syndrome (HPT-JT), parathyroid cancer and other disorders. Parafibromin, together with Paf1, Leo1, Ctr9 and WDR61, comprise the human Paf1 Complex, which interacts with RNA Polymerase II and regulates transcription and other cellular processes. Despite the identification of these parafibromin-interacting protein partners, whether, and the extent to which, they account for parafibromin’s tumor suppressor function is not clearly understood. Also unknown is the effect of starvation on parafibromin interactions. Previous experiments in flies suggested that heterozygous mutation of hyrax, the parafibromin homolog, conferred starvation resistance. In this study, we use a proteomic approach to identify novel parafibromin protein partners to understand its tumor suppressor function and effects of starvation. We overexpressed epitope-tagged wild-type parafibromin and the known HPT-JT-associated missense mutation L95P-parafibromin in mammalian cells and performed affinity purifications. We also purified parafibromin from cells that were grown in nutrient-present or starved medium for two hours. Eluates from the purifications were analyzed by mass spectrometry. All Paf1 Complex proteins were identified from numerous mass spectrometric experiments and served as internal controls. Several proteins that have repeatedly appeared in the analyses are being evaluated as potential interaction partners. A rough quantitative comparison of peptides from normal and starved cells was used to identify parafibromin partners that interact under different nutrition conditions. Further experimentation will be used to identify and validate novel parafibromin protein partners to help us understand parafibromin’s tumor suppressor role.

Scientific Focus Area: Cancer Biology

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