Elucidation of the link between the control of cell-cell adhesion by regulations of cell polarity and cell proliferation and differentitation

LAP(富亮氨酸重复序列(LRR)和PSD-95/DLG/ZO-1(PDZ))家族蛋白包括Scribble、Let-413、Erbin、Densin-180和Lano，参与细胞极性的调节。据报道，LAP蛋白的LRR结构域调节其基侧膜的定位，并对其功能至关重要。为了进一步剖析Erbin的质膜定位机制，我们将Erbin的各种突变体导入培养细胞中，并观察了Erbin在细胞内的定位。当在氨基(N)末端缺失1-32个氨基酸残基的LRR区突变体在细胞中过表达时，突变体不定位于质膜，而定位于细胞质。我们发现Erbin N-末端的半胱氨酸14和16在体内是棕榈酰化的。半胱氨酸14和/或半胱氨酸16转变为丝氨酸的突变体没有在质膜上定位，这表明Erbin的棕榈酰化是其质膜定位所必需的。Erbin过表达的1-196个氨基酸片段没有LRR的后半部分，是棕榈酰化的，但不定位在质膜上。这些结果表明，Erbin的质膜定位既需要棕榈酰化，也需要LRR。

LAP(leucine-rich repeats(LRR) and PSD-95/Dlg/ZO-1(PDZ)) family proteins, including Scribble, LET-413, ERBIN, Densin-180, and Lano, are involved in the regulation of cell polarity. The LRR domains of LAP proteins were reported to mediate their basolateral membrane localization and to be essential for their function. To further dissect the mechanism of the plasma membrane localization of ERBIN, we introduced various mutants of ERBIN into cultured cells and observed the intracellular localization. When an LRR domain mutant lacking amino acid residues 1-32 at the amino(N) terminal region was overexpressed in cells, the mutant did not localize at the plasma membrane, but localized in the cytoplasm. We found that cysteines 14 and 16 at the N-terminal region of ERBIN are in vivo palmitoylated. Overexpression of the mutants in which cysteine 14 and/or cysteine 16 were changed to serines did not localize at the plasma membrane, indicating that the palmitoylation of ERBIN is necessary for its plasma membrane localization. The overexpressed 1-196 amino acids fragment of ERBIN, which lacked the latter half of LRR, was palmitoylated but did not localize at the plasma membrane. These results suggest that both palmitoylation and LRR are required for the plasma membrane localization of ERBIN.