Vilk G, Saulnier R B, St Pierre R, Litchfield D W
Department of Biochemistry, Health Sciences Center, University of Western Ontario, London, Ontario N6A 5C1, Canada.
J Biol Chem. 1999 May 14;274(20):14406-14. doi: 10.1074/jbc.274.20.14406.
Protein kinase CK2 (formerly casein kinase II) exhibits elevated expression in a variety of cancers, induces lymphocyte transformation in transgenic mice, and collaborates with Ha-Ras in fibroblast transformation. To systematically examine the cellular functions of CK2, human osteosarcoma U2-OS cells constitutively expressing a tetracycline-regulated transactivator were stably transfected with a bidirectional plasmid encoding either catalytic isoform of CK2 (i.e. CK2alpha or CK2alpha') together with the regulatory CK2beta subunit in order to increase the cellular levels of either CK2 isoform. To interfere with either CK2 isoform, cells were also transfected with kinase-inactive CK2alpha or CK2alpha' (i. e. GK2alpha (K68M) or CK2alpha'(K69M)) together with CK2beta. In these cells, removal of tetracycline from the growth medium stimulated coordinate expression of catalytic and regulatory CK2 subunits. Increased expression of active forms of CK2alpha or CK2alpha' resulted in modest decreases in cell proliferation, suggesting that optimal levels of CK2 are required for optimal proliferation. By comparison, the effects of induced expression of kinase-inactive CK2alpha differed significantly from the effects of induced expression of kinase-inactive CK2alpha'. Of particular interest is the dramatic attenuation of proliferation that is observed following induction of CK2alpha'(K69M), but not following induction of CK2alpha(K68M). These results provide evidence for functional specialization of CK2 isoforms in mammalian cells. Moreover, cell lines exhibiting regulatable expression of CK2 will facilitate efforts to systematically elucidate its cellular functions.
蛋白激酶CK2（以前称为酪蛋白激酶II）在多种癌症中表达升高，可诱导转基因小鼠的淋巴细胞转化，并在成纤维细胞转化中与Ha-Ras协同作用。为了系统地研究CK2的细胞功能，将组成型表达四环素调节反式激活因子的人骨肉瘤U2-OS细胞稳定转染双向质粒，该质粒编码CK2的任一催化亚型（即CK2α或CK2α'）以及调节性CK2β亚基，以提高任一CK2亚型的细胞水平。为了干扰任一CK2亚型，细胞还被转染了激酶失活的CK2α或CK2α'（即GK2α(K68M)或CK2α'(K69M)）以及CK2β。在这些细胞中，从生长培养基中去除四环素可刺激催化性和调节性CK2亚基的协同表达。CK2α或CK2α'活性形式的表达增加导致细胞增殖适度下降，表明最佳的CK2水平是最佳增殖所必需的。相比之下，激酶失活的CK2α诱导表达的效果与激酶失活的CK2α'诱导表达的效果有显著差异。特别有趣的是，诱导CK2α'(K69M)后观察到增殖显著减弱，但诱导CK2α(K68M)后未观察到这种情况。这些结果为CK2亚型在哺乳动物细胞中的功能特化提供了证据。此外，表现出可调节CK2表达的细胞系将有助于系统地阐明其细胞功能。
