Santin A D, Hermonat P L, Ravaggi A, Chiriva-Internati M, Pecorelli S, Parham G P
Department of Obstetrics and Gynecology, University of Arkansas for the Medical Sciences, Little Rock 72205-7199, USA.
Cancer. 1998 Dec 1;83(11):2346-52. doi: 10.1002/(sici)1097-0142(19981201)83:11<2346::aid-cncr14>3.0.co;2-g.
Human papillomavirus (HPV) infection represents the most important risk factor for cervical carcinoma. Levels of expression of E6 and E7 transforming oncoproteins of high risk HPV genotypes (i.e., HPV-16 and HPV-18) have been linked specifically to the mitotic activity of cervical carcinoma and appear to be necessary for maintaining the malignant phenotype. However, E6/E7 viral proteins recently have been reported to be effective tumor rejection antigens in animal models and humans. Radiation treatment represents a standardized and effective modality for contemporary cervical carcinoma therapy. However, although the physiologic and cellular changes associated with high doses of irradiation have been well documented it has been shown only recently that an increased synthesis of specific cellular proteins is observed after irradiation. In this study, the authors analyzed the effects of high doses of gamma irradiation on the expression of E6/E7 oncoproteins in HPV-16-infected cervical carcinoma cell lines. In addition, the effects of radiation on major histocompatibility complex (MHC) restriction elements also were studied.
The effect of high doses of gamma irradiation (i.e., 1250, 2500, 5000, and 10,000 centigray [cGy]) on the kinetics of E6/E7 oncoprotein expression in two HPV-16 positive cervical carcinoma cell lines (i.e., CaSki and SiHa) was evaluated by Northern blot analysis. In addition, the effect of radiation on the expression of MHC molecules also was studied by Northern blot and fluorescence activator cell sorter (FACS) analysis.
Dose ranging from 1250 (sublethal) to 10,000 (lethal) cGy significantly increased the expression of E6/E7 oncoproteins as well as MHC Class I molecules in CaSki and SiHa cell lines when compared with untreated tumor cells. Both cell lines showed increased mRNA expression for MHC Class I molecules in a dose-dependent manner. E6/E7 oncoproteins also were up-regulated in a dose-dependent manner in the CaSki cell line, whereas in the SiHa cell line their expression plateau at 5000 cGy. When the kinetics of radiation-induced up-regulation of E6/E7 were studied, persistent up-regulation of the viral oncoproteins was noted for all doses of irradiation, with the lower and sublethal doses (i.e., 1250-2500 cGy) inducing the most significant enhancement.
High doses of irradiation can induce a significant and long-lasting up-regulation of E6/E7 oncogenes and MHC Class I restriction elements on HPV positive cervical carcinoma cell lines. These effects by themselves suggest that irradiation could enhance local tumor immunogenicity in patients receiving radiation therapy. However, in contrast to this possible beneficial effect, sublethal tumor irradiation (up-regulating E6/E7 transforming oncoproteins) also could confer a significant growth advantage to radiation-resistant tumor cells. These findings, combined with the previously reported acquisition of a radiation-induced drug resistance, could provide a biologic basis for the poor prognosis of patients with cervical carcinoma recurrence after radiation therapy.
人乳头瘤病毒（HPV）感染是宫颈癌最重要的危险因素。高危型HPV基因型（即HPV - 16和HPV - 18）的E6和E7转化癌蛋白的表达水平与宫颈癌的有丝分裂活性密切相关，并且似乎是维持恶性表型所必需的。然而，最近有报道称E6/E7病毒蛋白在动物模型和人类中是有效的肿瘤排斥抗原。放射治疗是当代宫颈癌治疗的一种标准化且有效的方式。然而，尽管与高剂量辐射相关的生理和细胞变化已有充分记录，但直到最近才发现辐射后会观察到特定细胞蛋白的合成增加。在本研究中，作者分析了高剂量γ射线辐射对HPV - 16感染的宫颈癌细胞系中E6/E7癌蛋白表达的影响。此外，还研究了辐射对主要组织相容性复合体（MHC）限制元件的影响。
通过Northern印迹分析评估高剂量γ射线辐射（即1250、2500、5000和10000厘戈瑞[cGy]）对两种HPV - 16阳性宫颈癌细胞系（即CaSki和SiHa）中E6/E7癌蛋白表达动力学的影响。此外，还通过Northern印迹和荧光激活细胞分选仪（FACS）分析研究了辐射对MHC分子表达的影响。
与未处理的肿瘤细胞相比，剂量范围从1250（亚致死）到10000（致死）cGy的辐射显著增加了CaSki和SiHa细胞系中E6/E7癌蛋白以及MHC I类分子的表达。两种细胞系中MHC I类分子的mRNA表达均呈剂量依赖性增加。CaSki细胞系中E6/E7癌蛋白也呈剂量依赖性上调，而在SiHa细胞系中，其表达在5000 cGy时达到平台期。当研究辐射诱导的E6/E7上调动力学时，发现所有辐射剂量下病毒癌蛋白均持续上调，其中较低和亚致死剂量（即1250 - 2500 cGy）诱导的增强最为显著。
高剂量辐射可诱导HPV阳性宫颈癌细胞系中E6/E7癌基因和MHC I类限制元件显著且持久地上调。这些效应本身表明辐射可增强接受放射治疗患者的局部肿瘤免疫原性。然而，与这种可能的有益效应相反，亚致死剂量的肿瘤辐射（上调E6/E7转化癌蛋白）也可能赋予耐辐射肿瘤细胞显著的生长优势。这些发现，结合先前报道的辐射诱导的耐药性，可为放射治疗后宫颈癌复发患者预后不良提供生物学基础。
