Perinucleolar compartment and transformation.

The perinucleolar compartment (PNC) is a sub-nuclear structure that preferentially localizes to the nucleolar periphery. The PNC is found predominantly in transformed cells both in vitro and in vivo. PNC prevalence (the percentage of cells containing at least one PNC) positively correlates with the progression of breast cancer and patient survival. PNCs are highly enriched with newly synthesized RNA polymerase III transcripts and RNA-binding proteins. The structural integrity of the PNC is dependent upon the transcription of these RNAs and a critical level of the polypyrimidine tract binding (PTB) protein, as assayed by the localization of other PNC-associated proteins. These observations suggest a model in which the PNC is a dynamic, functional organelle that forms under specific physiological conditions favoring cellular transformation and might be involved in the metabolism of RNA polymerase III transcripts.