Smits P H, Smits H L, Minnaar R P, Hemmings B A, Mayer-Jaekel R E, Schuurman R, van der Noordaa J, ter Schegget J
Department of Medical Microbiology, University of Amsterdam, The Netherlands.
EMBO J. 1992 Dec;11(12):4601-6. doi: 10.1002/j.1460-2075.1992.tb05562.x.
Previous results indicated that SV40 small t is essential for SV40-induced transformation of diploid cells but dispensable for the transformation of cells with a deletion on the short arm of chromosome 11 (del-11 cells). From these results we concluded that del-11 cells contain a cellular 'SV40 small t-like' factor, which is able to transactivate the HPV16 long control region (LCR) and to complement SV40 large T in transformation. Since SV40 small t and the regulatory 55 kDa subunit (PR55) of protein phosphatase 2A (PP2A), have been shown to inhibit the enzyme activity of PP2A, the PR55 beta subunit could be the putative 'small t-like' factor. In accordance with this hypothesis, we show that the PR55 beta subunit is highly expressed in del-11 but not in diploid cells and is able to trans-activate the HPV16 LCR in diploid cells. Moreover, inhibition of PP2A by okadaic acid resulted in trans-activation of the HPV16 LCR in diploid cells. Alignment of PR55 and SV40 small t showed a common four amino acid motif DKGG. We present evidence that the integrity of this motif is necessary for the PP2A-mediated ability of SV40 small t to trans-activate the HPV16 LCR.
先前的结果表明，SV40小t抗原对于SV40诱导的二倍体细胞转化至关重要，但对于11号染色体短臂缺失的细胞（del-11细胞）的转化则并非必需。从这些结果我们得出结论，del-11细胞含有一种细胞内的“SV40小t样”因子，它能够反式激活人乳头瘤病毒16型（HPV16）长控制区（LCR）并在转化过程中补充SV40大T抗原的功能。由于SV40小t抗原和蛋白磷酸酶2A（PP2A）的55 kDa调节亚基（PR55）已被证明可抑制PP2A的酶活性，因此PR55β亚基可能是假定的“小t样”因子。根据这一假设，我们发现PR55β亚基在del-11细胞中高表达，但在二倍体细胞中不表达，并且能够在二倍体细胞中反式激活HPV16 LCR。此外，冈田酸对PP2A的抑制导致二倍体细胞中HPV16 LCR的反式激活。PR55和SV40小t抗原的比对显示出一个共同的四氨基酸基序DKGG。我们提供的证据表明，该基序的完整性对于SV40小t抗原通过PP2A介导反式激活HPV16 LCR的能力是必需的。
