The nucleolus, a subnuclear organelle, is a site for ribosome biogenesis during cellular growth. Considerable efforts have been invested in deciphering the makeup of nucleolar resident proteins and how they contribute to nucleolar functions. Despite the many advances made in determining the composition of the nucleolar proteome, it is still unclear how most of this resident nucleolar proteins function. Poly (ADP-ribose)polymerase 1 (PARP1) is one of the many resident nucleolar proteins whose function in the nucleolus is not clearly defined. PARP1 utilizes nicotinamide adenine dinucleotide (NAD+) as a substrate to generate (ADP) ribose (ADPr) to modify acceptor proteins. Interestingly, it is estimated that about 50% of total PARP1 is found in the nucleolus. Loss of PARP1 activity causes mislocalization of nucleolar specific proteins, which may cause loss of an intact nucleolar structure. The question whether PARP1's regulation of nucleolar integrity impacts nucleolar functions remains unknown. This proposal aims to expand on our previously reported observation by investigating the role of PARP1 in nucleolar structure and functions, specifically ribosome biogenesis. To achieve our objectives, we will utilize confocal microscopy and immunofluorescence to examine localization of nucleolar specific proteins in salivary glands from Drosophila larvae with compromised PARP1 activity. Northern blot of rRNA transcripts will be used to analyze the effect of disrupting PARP1 activity on rRNA processing and modification. We will examine the incorporation of fluorescence tagged RpL22 and RpL23 ribosomal proteins into the translation machinery in flies with compromised PARP1 activity using polysome gradient, immunoprecipitation, and Western blot analysis.
PARP1 activity has become an important clinical target in the war against cancer, yet aside from its presence in the nucleolus, very little is known about its influence in this important subnuclear structure. This proposal will uncover a novel and exciting role for PARP1, which may have significant impact on cancer treatment regimens.