Linggi B, Cheng Q C, Rao A R, Carpenter G
Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232-0146, USA.
Oncogene. 2006 Jan 5;25(1):160-3. doi: 10.1038/sj.onc.1209003.
The ErbB-4 receptor tyrosine kinase homo- and heterodimerizes following heregulin binding, which provokes increased levels of tyrosine autophosphorylation. Unique to the ErbB family, ErbB-4 is then proteolytically cleaved by alpha- and gamma-secretase to produce an 80 kDa intracellular domain (s80 ICD) fragment. This fragment is found in both the cytoplasm and nucleus of many normal and cancer cells and can interact with transcription factors in the cytoplasm and nucleus. Since the s80 ICD lacks ectodomain sequences known to play a major role in dimerization of ErbB family members, we asked whether the s80 ICD is an active tyrosine kinase. Here, we demonstrate that the s80 ICD is a constitutively active tyrosine kinase and can form homodimers. The s80 ICD is autophosphorylated in cells and can phosphorylate an exogenous substrate in vitro. Also, the s80 ICD can coassociate and dimers are detected by chemical crosslinking. This is the first example of constitutive kinase activation and dimerization totally within the cytoplasmic domain of an ErbB receptor and suggests that the s80 ICD may function to phosphorylate substrates in the cytoplasm or nucleus.
在这里，表皮生长因子（HRG）结合后，ErbB-4受体酪氨酸激酶会发生同源和异源二聚化，这会导致酪氨酸自身磷酸化水平升高。ErbB-4是ErbB家族特有的，随后会被α-和γ-分泌酶进行蛋白水解切割，产生一个80 kDa的细胞内结构域（s80 ICD）片段。在许多正常细胞和癌细胞的细胞质和细胞核中都能发现这个片段，并且它可以与细胞质和细胞核中的转录因子相互作用。由于s80 ICD缺乏已知在ErbB家族成员二聚化中起主要作用的胞外结构域序列，我们不禁要问s80 ICD是否是一种活性酪氨酸激酶。在这里，我们证明s80 ICD是一种组成型活性酪氨酸激酶，并且可以形成同源二聚体。s80 ICD在细胞中会发生自身磷酸化，并且在体外可以磷酸化外源性底物。此外，s80 ICD可以共同结合，并且通过化学交联检测到二聚体。这是ErbB受体细胞质结构域内完全组成型激酶激活和二聚化的首个例子，表明s80 ICD可能在细胞质或细胞核中磷酸化底物发挥作用。
