Barbosa M S, Edmonds C, Fisher C, Schiller J T, Lowy D R, Vousden K H
Laboratory of Cellular Oncology, National Cancer Institute, NIH Bethesda, MD 20892.
EMBO J. 1990 Jan;9(1):153-60. doi: 10.1002/j.1460-2075.1990.tb08091.x.
Some genital human papillomavirus (HPV) types, such as 16 and 18, are highly associated with malignant cervical tumors while others, such as HPV 6, are only rarely found in these malignancies. The E7 oncoproteins of HPV 6, 16 and 18 each have a 17 amino acid region with striking homology to adenovirus E1a and SV40 LT. E1a, LT and the E7 oncoprotein of HPV16 all bind the cellular Rb protein in vitro, and for E1a and LT this region of homology contains sequences essential for interaction with Rb. We have now found that in HPV 16 E7 this region (amino acids 21-37) contains two separate biochemical activities, each of which contributes to E7-mediated transformation. Rb binding was localized to the N terminus of this region, while the C terminus was shown to serve as a substrate for casein kinase (CK) II, which phosphorylated serine-31 and serine-32. Replacement of the two serines by non-phosphorylatable amino acids led to a reduction in transforming activity and abolished phosphorylation but did not affect Rb binding. Rb binding and CK II phosphorylation were also examined for the E7 proteins of HPV 6 and HPV 18. HPV 16 and 18 E7 bound similar amounts of Rb, but HPV 6 E7 consistently bound less. Phosphorylation rates also varied, with HPV 18 E7 being 2-fold faster than HPV 16 E7, which in turn was 2-fold faster than HPV 6 E7. We conclude that Rb binding and phosphorylation of E7 by CKII are independent activities which are required for efficient transformation by E7 and that these activities correlate directly with the relative oncogenic potential of these viruses.
某些生殖器人乳头瘤病毒（HPV）类型，如16型和18型，与宫颈恶性肿瘤高度相关，而其他类型，如HPV 6型，在这些恶性肿瘤中很少见。HPV 6、16和18的E7癌蛋白各自有一个17个氨基酸的区域，与腺病毒E1a和SV40大T抗原具有显著的同源性。E1a、大T抗原和HPV16的E7癌蛋白在体外均能结合细胞Rb蛋白，对于E1a和大T抗原，这个同源区域包含与Rb相互作用所必需的序列。我们现在发现，在HPV 16 E7中，这个区域（氨基酸21 - 37）包含两种独立的生化活性，每种活性都有助于E7介导的转化。Rb结合定位于该区域的N端，而C端被证明是酪蛋白激酶（CK）II的底物，CK II使丝氨酸31和丝氨酸32磷酸化。用不可磷酸化的氨基酸取代这两个丝氨酸导致转化活性降低并消除了磷酸化，但不影响Rb结合。我们还检测了HPV 6和HPV 18的E7蛋白的Rb结合和CK II磷酸化情况。HPV 16和18 E7结合的Rb量相似，但HPV 6 E7始终结合较少。磷酸化速率也有所不同，HPV 18 E7的磷酸化速率比HPV 16 E7快2倍，而HPV 16 E7又比HPV 6 E7快2倍。我们得出结论，Rb结合和CKII对E7的磷酸化是独立的活性，是E7有效转化所必需的，并且这些活性与这些病毒的相对致癌潜力直接相关。
