Wu T T, Castle J D
Department of Cell Biology, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908, USA.
Mol Biol Cell. 1998 Jul;9(7):1661-74. doi: 10.1091/mbc.9.7.1661.
Secretory carrier membrane proteins (SCAMPs) are ubiquitously expressed proteins of post-Golgi vesicles. In the presence of the tyrosine phosphatase inhibitor vanadate, or after overexpression in Chinese hamster ovary (CHO) cells, SCAMP1 and SCAMP3 are phosphorylated selectively on tyrosine residue(s). Phosphorylation is reversible after vanadate washout in situ or when isolated SCAMP3 is incubated with the recombinant tyrosine phosphatase PTP1B. Vanadate also causes the partial accumulation of SCAMP3, but not SCAMP1, in "patches" at or near the cell surface. A search for SCAMP kinase activities has shown that SCAMPs 1 and 3, but not SCAMP2, are tyrosine phosphorylated in EGF-stimulated murine fibroblasts overexpressing the EGF receptor (EGFR). EGF catalyzes the progressive phosphorylation of the SCAMPs up to 1 h poststimulation and may enhance colocalization of the EGFR and SCAMP3 within the cell interior. EGF also induces SCAMP-EGFR association, as detected by coimmunoprecipitation, and phosphorylation of SCAMP3 is stimulated by the EGFR in vitro. These results suggest that phosphorylation of SCAMPs, either directly or indirectly, may be functionally linked to the internalization/down-regulation of the EGFR.
分泌载体膜蛋白（SCAMPs）是高尔基体后囊泡中普遍表达的蛋白质。在酪氨酸磷酸酶抑制剂钒酸盐存在的情况下，或者在中国仓鼠卵巢（CHO）细胞中过表达后，SCAMP1和SCAMP3在酪氨酸残基上被选择性磷酸化。在原位洗脱钒酸盐后，或者将分离的SCAMP3与重组酪氨酸磷酸酶PTP1B一起孵育时，磷酸化是可逆的。钒酸盐还会导致SCAMP3在细胞表面或其附近的“斑块”中部分积累，但不会导致SCAMP1积累。对SCAMP激酶活性的研究表明，在过表达表皮生长因子受体（EGFR）的表皮生长因子（EGF）刺激的小鼠成纤维细胞中，SCAMP1和3会发生酪氨酸磷酸化，但SCAMP2不会。EGF在刺激后1小时内催化SCAMPs的逐步磷酸化，并可能增强EGFR和SCAMP3在细胞内的共定位。通过共免疫沉淀检测发现，EGF还诱导SCAMP与EGFR结合，并且在体外，EGFR刺激SCAMP3的磷酸化。这些结果表明，SCAMPs的磷酸化，无论是直接还是间接的，都可能在功能上与EGFR的内化/下调相关。
