Rearrangement of nuclear ribonucleoproteins and extrusion of nucleolus-like bodies during apoptosis induced by hypertonic stress

Short-term hypertonic (HT) stress induces apoptotic cell death in human EUE cells in culture, as observed by electron microscopy, agarose-gel electrophoresis of low-molecular-weight DNA, DNA flow cytometry and annexin-V-propidium iodide double-staining. During HT-induced apoptosis, nuclear ribonucleoprotein (RNP)-containing structures undergo rearrangement, with the formation of Heterogeneous Ectopic RNP-Derived Structures (HERDS) which pass into the cytoplasm, as already reported for other examples of spontaneous and drug-induced apoptosis. Of special interest was the observation that nucleoluslike bodies (NLBs) which resemble morphologically nuclear functional nucleoli may be extruded into the cytoplasm of apoptotic cells and are observed inside the cytoplasmic fragments blebbing- out at the cell surface; these NLBs still contain immunodetectable nucleolar proteins (such as fibrillarin). This is an additional example of RNPcontaining structures of nuclear origin which are extruded from the nucleus, in an almost “native” form, during apoptosis.