Li Mengsen, Li Hui, Li Chaoying, Zhou Sheng, Guo Liyuan, Liu Han, Jiang Wei, Liu Xinhua, Li Pingfeng, McNutt Michael A, Li Gang
Department of Biochemistry and Molecular Biology, Peking University Health Science Center, Beijing, China.
Int J Cancer. 2009 Jun 15;124(12):2845-54. doi: 10.1002/ijc.24272.
Although there is increasing evidence that alpha fetoprotein (AFP) may function as regulatory factor in the growth of tumor cells, the precise mechanism is still unclear. In the current study, we investigated the role of the cytoplasmic AFP in caspase-3-mediated signaling of apoptosis. Our results showed that low doses of TNF-related apoptosis-inducing ligand (TRAIL) elevated the activity of caspase-8, but not caspase-3. Caspase-3 colocalized and interacted with AFP in the cytoplasm of Bel 7402 cells, and translocated into nuclei in association with the occurrence of apoptosis while cells were under cotreatment with all-trans retinoic acid (ATRA) or TRAIL. AFP was able to form complexes with caspase-3 and block onward transmission of signaling from caspase-8. Knockdown of AFP increased the sensitivity of Bel 7402 cells to TRAIL, and thereby, triggered caspase-3 signaling. No intermolecule interaction occurred between AFP and caspase-8, nor was caspase-8 activity altered after AFP knockdown, demonstrating the selectivity of AFP in interfering with the apoptotic signaling pathway. The effect of AFP on caspase-3 was further confirmed by transfection of the AFP gene into HLE cells (AFP negative). We conclude that ATRA or TRAIL resistance in AFP producing hepatoma is at least, in part, attributable to the high level of the cytoplasmic AFP. Therefore, it is possible that the combination of AFP gene silencing together with ATRA/TRAIL cotreatment will benefit the enhancement of the chemotherapeutic efficiency of these agents on tumors.
尽管越来越多的证据表明甲胎蛋白（AFP）可能在肿瘤细胞生长中作为调节因子发挥作用，但其确切机制仍不清楚。在本研究中，我们调查了细胞质AFP在半胱天冬酶-3介导的凋亡信号传导中的作用。我们的结果表明，低剂量的肿瘤坏死因子相关凋亡诱导配体（TRAIL）可提高半胱天冬酶-8的活性，但不能提高半胱天冬酶-3的活性。在Bel 7402细胞的细胞质中，半胱天冬酶-3与AFP共定位并相互作用，并在细胞与全反式维甲酸（ATRA）或TRAIL联合处理时，随着凋亡的发生而转位到细胞核中。AFP能够与半胱天冬酶-3形成复合物，并阻断来自半胱天冬酶-8的信号进一步传递。敲低AFP可增加Bel 7402细胞对TRAIL的敏感性，从而触发半胱天冬酶-3信号传导。AFP与半胱天冬酶-8之间未发生分子间相互作用，AFP敲低后半胱天冬酶-8的活性也未改变，这表明AFP在干扰凋亡信号通路方面具有选择性。将AFP基因转染到HLE细胞（AFP阴性）中进一步证实了AFP对半胱天冬酶-3的作用。我们得出结论，产生AFP的肝癌细胞对ATRA或TRAIL耐药至少部分归因于细胞质AFP的高水平。因此，AFP基因沉默与ATRA/TRAIL联合处理相结合可能有利于提高这些药物对肿瘤的化疗效率。
