Alternative subcellular locations of keratinocyte basonuclin.

Basonuclin is a zinc finger protein present in the basal cell layer of the epidermis and in hair follicles. Human basal epidermal cells are often heterogeneous with respect to a nuclear or cytoplasmic location of basonuclin and the protein may be concentrated in either compartment. In mouse and rat epidermis, although clusters of basonuclin may be seen in some basal cell nuclei, the protein is mainly concentrated in the cytoplasm. When epidermis whose basal cells contain predominantly cytoplasmic basonuclin is disaggregated and the cells are cultivated in the presence of supporting 3T3 cells, the basonuclin of the growing keratinocyte colonies is strongly concentrated in the cell nuclei. Transfer of the cells to culture medium without supporting 3T3 cells results in a predominantly cytoplasmic concentration of the basonuclin. This translocation is reversible, since addition of supporting 3T3 cells restores most basonuclin to the nucleus. The nuclear location is associated with more rapid cell growth. We conclude that different states of the keratinocyte require greater or less activity of basonuclin, and the subcellular location of the protein is probably related to the magnitude of its action on the cells.