Emeritus Professor and Consultant Pathologist, NIRTLD, Masih Daneshvari Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
The nucleolus is an intranuclear membrane-less organelle. It is involved in ribosome biogenesis and protein synthesis. When the demand for protein synthesis increases in cell growth and proliferation (e.g., tumors), the cell upregulates ribosome biogenesis. Changes in nucleolar size and number have been recognized as known features of many tumor types. Recent evidence suggests that overproduction of ribosome, decreased ribosome biogenesis, and quantitative and qualitative changes in the nucleolus function, may result in oncogenesis. Today, it is clear that the nucleolus is involved in processes other than ribosome biogenesis. Other functions of the nucleolus include detecting and responding to endogenous and exogenous stress, maintaining genome stability, and regulating cell cycle progression, telomere function, cellular senescence, gene expression, and chromatin structure. Alterations in many of these fundamental nucleolar processes may contribute to the formation of cancer cell phenotypes. This phenomenon suggests that normal nucleolar functions are a safeguard against the development of malignancies and have potential therapeutic effects, as reported in non-small-cell lung carcinoma and other malignancies.