Glineur C, Bailly M, Ghysdael J
INSERM U186/CNRS UA 1160, Institut Pasteur, Lille, France.
Oncogene. 1989 Oct;4(10):1247-54.
The c-erbA alpha progenitor of the v-erbA oncogene of avian erythroblastosis virus (AEV) encodes a nuclear receptor for the thyroid hormone triiodothyronine (T3) which acts as a ligand-dependent transcription factor. As previously reported (Goldberg et al., EMBO J., 7, 2425-2433), the 46 kd chicken c-erbA alpha-encoded T3 receptor (ck-ErbA alpha) is phosphorylated at two major sites. Only one of these sites (Ser28/Ser29) is retained in the v-erbA-encoded P75gag-v-erbA protein. We report here the identification of the second phosphorylation site of ck-ErbA alpha as a single serine residue localized at position 12. We propose that casein kinase II, a protein kinase distributed in the cytosolic and nuclear compartments of a number of different tissues, is responsible for serine 12 phosphorylation on the following grounds. First, serine 12 is part of a sequence containing multiple acidic amino-acids, a feature common to all sites phosphorylated by casein kinase II in physiological substrates. Second, ck-ErbA alpha was found to be phosphorylated by purified casein kinase II in vitro at the same site, as defined by two-dimensional mapping experiments, as that observed in vivo. Third, conversion of serine 12 into an unphosphorylatable alanine residue by site directed mutagenesis abolishes the phosphorylation of ck-ErbA alpha by casein kinase II in vitro. Phosphorylation of serine 12 is likely to play a role in the modulation of ErbA alpha function since both serine 12 and the casein kinase II phosphorylation sequence motif are phylogenetically conserved in all known members of the c-erbA alpha gene family encoding T3 binding proteins. The codon specifying serine 12 in ck-ErbA alpha being precisely the point where recombination between gag and ck-c-erbA alpha occurred to generate v-erbA, our results furthermore suggest that deletion of serine 12 could contribute to the oncogenic activation of v-erbA.
禽成红细胞增多症病毒（AEV）的v-erbA癌基因的c-erbAα前体编码一种甲状腺激素三碘甲状腺原氨酸（T3）的核受体，该受体作为一种依赖配体的转录因子发挥作用。如先前报道（Goldberg等人，《欧洲分子生物学组织杂志》，7，2425 - 2433），46kd的鸡c-erbAα编码的T3受体（ck-ErbAα）在两个主要位点被磷酸化。这些位点中只有一个（Ser28/Ser29）保留在v-erbA编码的P75gag-v-erbA蛋白中。我们在此报告，ck-ErbAα的第二个磷酸化位点被鉴定为位于第12位的单个丝氨酸残基。基于以下理由，我们提出酪蛋白激酶II（一种分布于许多不同组织的胞质和核区室的蛋白激酶）负责丝氨酸12的磷酸化。首先，丝氨酸12是包含多个酸性氨基酸的序列的一部分，这是酪蛋白激酶II在生理底物中磷酸化的所有位点共有的特征。其次，通过二维图谱实验确定，体外纯化的酪蛋白激酶II在与体内观察到的相同位点使ck-ErbAα磷酸化。第三，通过定点诱变将丝氨酸12转化为不可磷酸化的丙氨酸残基，消除了酪蛋白激酶II在体外对ck-ErbAα的磷酸化作用。丝氨酸12的磷酸化可能在ErbAα功能的调节中起作用，因为丝氨酸12和酪蛋白激酶II磷酸化序列基序在所有已知的编码T3结合蛋白的c-erbAα基因家族成员中在系统发育上都是保守的。ck-ErbAα中指定丝氨酸12的密码子恰好是gag与ck-c-erbAα之间发生重组以产生v-erbA的位点，我们的结果进一步表明丝氨酸12的缺失可能有助于v-erbA的致癌激活。
