Iuchi S, Green H
Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston MA 02115, USA.
Proc Natl Acad Sci U S A. 1997 Jul 22;94(15):7948-53. doi: 10.1073/pnas.94.15.7948.
Basonuclin is a zinc-finger protein found in basal cells of the epidermis. In human keratinocyte cultures, basonuclin is susceptible to serine-phosphorylation and the addition of the phosphatase inhibitor, okadaic acid, promotes accumulation of basonuclin in the cytoplasm. The region of basonuclin containing the nuclear localization signal of basonuclin is necessary for nuclear localization of the protein and Ser-541, located immediately C-terminal to the nuclear localization signal, is the principal phosphorylation site in vitro. A nearly complete basonuclin transiently expressed in cultured keratinocytes localizes predominantly in the nucleus, but substitution of aspartic acid for Ser-541 promotes cytoplasmic localization. The same substitution of Ser-537 has a similar but weaker effect. Substitution of both serine residues by alanine leads to nuclear localization. These results show that nuclear localization of basonuclin depends on serine dephosphorylation, primarily of Ser-541. Different subcellular locations of basonuclin in different keratinocyte subtypes are therefore most likely to be controlled by the state of phosphorylation of Ser-541.
锌指蛋白存在于表皮基底细胞中。在人角质形成细胞培养物中，锌指蛋白易于发生丝氨酸磷酸化，添加磷酸酶抑制剂冈田酸可促进锌指蛋白在细胞质中积累。锌指蛋白中包含其核定位信号的区域对于该蛋白的核定位是必需的，位于核定位信号紧邻C端的Ser-541是体外主要的磷酸化位点。在培养的角质形成细胞中瞬时表达的几乎完整的锌指蛋白主要定位于细胞核，但将Ser-541替换为天冬氨酸会促进其细胞质定位。将Ser-537进行相同替换有类似但较弱的效果。将两个丝氨酸残基都替换为丙氨酸会导致核定位。这些结果表明，锌指蛋白的核定位取决于丝氨酸去磷酸化，主要是Ser-541的去磷酸化。因此，锌指蛋白在不同角质形成细胞亚型中的不同亚细胞定位很可能受Ser-541磷酸化状态的控制。
