ULTRASTRUCTURAL DISTRIBUTION OF THE DEATH-DOMAIN-CONTAINING MYD88 PROTEIN IN HELA-CELLS

MyD88, a protein implicated in interleukin-1 signaling, was localized in HeLa cells transiently transfected with an epitope-tagged (flag) ve rsion of MyD88. Overexpression of MyD88 can induce apoptosis. We have analyzed the fine structural intracellular distribution of MyD88 using immunoelectron microscopy. MyD88 is localized to the nucleus and to t he cytoplasm as revealed by immunofluorescence visualization. Ultrastr uctural immunocytochemistry shows that, in the cytoplasm, this protein is associated with fibrillar aggregates containing beta-actin. In the nucleus, MyD88 was found in fibrillar domains present only in cells n ot yet displaying morphological signs of apoptosis. These domains are not derived from nucleoli and do not constitute an accumulation site o f splicing factors. We suggest that such structures could be involved in the formation of the apoptotic bodies and/or in the modification of the nuclear structure and of nucleocytoplasmic trafficking during apo ptosis. (C) 1998 Academic Press.