ANNEXIN-I AND ANNEXIN-II SHOW DIFFERENCES IN SUBCELLULAR-LOCALIZATIONAND DIFFERENTIATION-RELATED CHANGES IN HUMAN EPIDERMAL-KERATINOCYTES

The annexins are a family of calcium-dependent phospholipid-binding pr oteins whose in vitro properties have led tee a number of hypotheses s uggesting their cellular functions, including membrane fusion in exocy tosis and endocytosis. To investigate the topography and possible func tions of these proteins we compared the subcellular localization of an nexins I, Il, IV and VI in skin sections and in cultured. epidermal ke ratinocytes by immunostaining. We found that annexin I staining was in a granular pattern in the monolayer epithelial cells but in an envelo pe pattern in the stratified keratinocytes. This finding corroborates previous reports that annexin I crosslinks to form cornified envelopes in the mid-epidermis and explains the absence of staining above that level. It is unlikely that this protein is related to exocytosis in th e granular layer of the epidermis, In comparison, annexin II staining was also granular and was detected in all nucleated epidermal cells as bands at the cell periphery, However, only annexin II was detected ex tracellularly among the top layer of cultured cells, The intracellular linear envelope pattern of annexin I and the intracellular pattern of annexin II suggest their interactions with the membrane cytoskeleton in other biological functions, Taken together, both annexins undergo d ifferent differentiation-related changes, While methanol fixation enha nced staining of annexin I, it diminished staining of annexin II. Thei r opposite responses to methanol fixative suggests a different molecul ar organization of the two annexins with phospholipid in the cell memb rane, Annexins IV and VI were predominantly confined to dermal cells i ncluding ductal and myoepithelial cells and were not detected in cultu red keratinocytes using either cold methanol fixative or prefixation l abeling.