Specific sequences in p120ctn determine subcellular distribution of its multiple isoforms involved in cellular adhesion of normal and malignant epithelial cells.
Specific sequences in p120ctn determine subcellular distribution of its multiple isoforms involved in cellular adhesion of normal and malignant epithelial cells.
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发表时间：
2002-04
影响因子：
4
通讯作者：
S. Aho;Laura Levänsuo;O. Montonen;C. Kari;U. Rodeck;J. Uitto
中科院分区：
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作者：
S. Aho;Laura Levänsuo;O. Montonen;C. Kari;U. Rodeck;J. Uitto
P120连环蛋白(P120ctn)属于Armadillo家族蛋白，与细胞间黏附和信号转导密切相关。由于选择性剪接和多个翻译起始密码子，一个基因可以表达几种p120ctn亚型。所有p120ctn亚型共享中央Armadillo重复结构域，但具有不同的N-末端和C-末端。人们对不同亚型的生物学功能知之甚少。在这项研究中，我们研究了各种p120ctn亚型在表皮来源的培养细胞中的分布及其表达的后果。免疫组织化学分析和Western blotting分析表明，黑素细胞和黑色素瘤细胞主要表达长亚型1A，而角质形成细胞主要表达短亚型，尤其是3A，它以钙依赖的方式定位于细胞-细胞黏附连接。在正常角质形成细胞和黑素细胞中检测到的最短亚型4A通常从鳞状细胞癌或黑色素瘤细胞中缺失。C端选择性剪接的外显子B存在于p120ctn转录本中，但在来自这些器官的几个肿瘤组织中缺失。为了测试p120ctn亚型是否具有不同的生物学功能，我们将表达载体瞬时导入黑色素瘤细胞(1205-Lu)和永生化角质形成细胞(HaCaT)。事实上，p120ctn的不同结构域负责其不同的生物学功能。显性分枝表型同样由异构体1A、2A和3A诱导，而最短的异构体4A则完全缺乏这种能力。此外，外显子B编码的序列，如在异构体1AB中，足以消除由异构体1A诱导的分枝表型。分枝表型的诱导与p120ctn异构体1A、2A和3A的核定位有关，而排除在核外的4A和1AB亚型不诱导分枝表型。N-末端序列包含8个酪氨酸残基中的7个，最近被认为是潜在的被Src激酶磷酸化的候选序列，是核定位和分支表型形成所必需的。最后，导致分枝表型的p120ctn亚型的表达与E-钙粘蛋白在HaCaT细胞中的细胞重新定位有关。总的来说，我们已经确定了p120ctn N末端的序列，这些序列是核定位和p120ctn诱导的分支表型的先决条件。肿瘤细胞中p120ctn胞浆池的缺失提示了这种异构体在正常细胞和组织中的重要功能。
P120 catenin (p120ctn) belongs to the Armadillo family of proteins, which is implicated in cell-cell adhesion and signal transduction. Owing to alternative splicing and multiple translation initiation codons, several p120ctn isoforms can be expressed from a single gene. All p120ctn isoforms share the central Armadillo repeat domain but have divergent N- and C-termini. Little is known about the biological functions of the different isoforms. In this study, we examined the distribution of various p120ctn isoforms and the consequences of their expression in cultured cells of epidermal origin. Immunohistochemical analysis and western blotting revealed that melanocytes and melanoma cells primarily express the long isoform 1A, whereas keratinocytes express shorter isoforms, especially 3A, which localize to cell-cell adhesion junctions in a calcium-dependent manner. The shortest isoform 4A, which was detected in normal keratinocytes and melanocytes, was generally lost from cells derived from squamous cell carcinomas or melanomas. The C-terminal alternatively spliced exon B was present in the p120ctn transcripts in the colon, intestine and prostate, but was lost in several tumor tissues derived from these organs. To test whether p120ctn isoforms serve in distinct biological functions, we transiently transfected the expression constructs into melanoma cells (1205-Lu) and immortalized keratinocytes (HaCaT). Indeed, distinct domains of p120ctn are responsible for its different biological functions. The prominent branching phenotype was induced equally by isoforms 1A, 2A and 3A, whereas the shortest isoform 4A, which was devoid of the N-terminal domain, completely lacked this ability. Also, the exon-B-encoded sequences, as in the isoform 1AB, were sufficient to abolish the branching phenotype as induced by the isoform 1A. The induction of the branching phenotype cosegregated with the nuclear localization of the p120ctn isoforms 1A, 2A and 3A, whereas the isoforms 4A and 1AB, which were excluded from the nucleus, did not induce the branching phenotype. The N-terminal sequences that contain seven out of eight tyrosine residues, recently characterized as potential candidates for phosphorylation by Src kinase, are required for the nuclear localization and for the formation of the branching phenotype. Finally, expression of the p120ctn isoforms, which caused the branching phenotype, was associated with cellular relocalization of E-cadherin in HaCaT cells. Collectively, we have identified sequences within the p120ctn N-terminus that are prerequisites for both nuclear localization and the p120ctn-induced branching phenotype. Loss of the cytoplasmic pool of p120ctn from tumor cells suggests an important function for such isoforms in normal cells and tissues.