ANNEXINS-II, ANNEXINS-IV, ANNEXINS-V AND ANNEXINS-VI RELOCATE IN RESPONSE TO RISES IN INTRACELLULAR CALCIUM IN HUMAN FORESKIN FIBROBLASTS

Annexins are a family of proteins implicated in a number of cellular p rocesses involving calcium. We studied annexins I, II, IV, V and VI an d found that they are all present in human foreskin fibroblasts and, f rom immunocytochemical studies, have distinct locations in the cell, O nly annexin IV and annexin V have unstructured cytoplasmic staining pa tterns consistent with predominantly cytosolic locations, Annexin VI p artially colocalizes with the endoplasmic reticulum, In contrast, anne xins I and II are both associated with the plasma membrane with annexi n II having a very homogeneous staining compared with the punctate pat tern observed for annexin I. Annexins I, IV and V are all present in t he nucleus at higher concentrations than in the cytoplasm, Treatment o f cells with the calcium ionophore A23187 to raise intracellular calci um, results in relocations of annexin II, IV, V and VI, Intranuclear a nnexins IV and V relocate to the nuclear membrane whereas the cytosoli c pools of these annexins relocate to the plasma membrane, Annexin II relocates to granular structures at the plasma membrane whereas annexi n VI relocates to a more homogeneous distribution on the plasma membra ne, These results are consistent with an important role for annexins i n mediating the calcium signal at the plasma membrane and within the n uclei of fibroblasts.