Department of Medical Research, National Taiwan University Hospital, Taipei, Taiwan.
PLoS One. 2013;8(2):e55705. doi: 10.1371/journal.pone.0055705. Epub 2013 Feb 1.
Previously, we reported that cancerous inhibitor of protein phosphatase 2A (CIP2A) mediates the apoptotic effect of bortezomib in hepatocellular carcinoma (HCC). Here, we report a proteasome-independent mechanism by which bortezomib induces autophagy in HCC. Our data indicate that bortezomib activated autophagy in a dose- and time- dependent manner in HCC cell lines including Huh-7, Sk-Hep1, and Hep3B. Bortezomib downregulated CIP2A, phospho-Akt (P-Akt) and phospho-4EBP1 (P-4EBP1) in a dose- and time-dependent manner in all tested HCC cells. Ectopic expression of CIP2A abolished the effect of bortezomib on autophagy. Co-treatment of bortezomib and calyculin A, a PP2A inhibitor, reduced the effect of bortezomib on P-Akt, P-4EBP1, and autophagy. Increased phosphorylation of either Akt or 4EBP1 by ectopic overexpression protected cells from bortezomib-induced autophagy. Furthermore, we examined the effect of ΔBtz, a bortezomib derivative that closely resembles bortezomib structurally but has no proteasome activity, in HCC. Interestingly, ΔBtz demonstrated similar effects to bortezomib on autophagy, CIP2A, P-Akt and P-4EBP1, suggesting that the effect of bortezomib on autophagy is independent of proteasome inhibition. Moreover, our in vivo data showed that both bortezomib and ΔBtz inhibited tumor growth, downregulated CIP2A, P-Akt and induced autophagy in Huh-7 tumors. In conclusion, bortezomib induces autophagy in HCC through a CIP2A-PP2A-Akt-4EBP1 pathway.
先前，我们报道了癌性蛋白磷酸酶 2A 抑制剂（CIP2A）介导硼替佐米在肝癌（HCC）中的凋亡作用。在这里，我们报告了硼替佐米在 HCC 中诱导自噬的一种蛋白酶体非依赖性机制。我们的数据表明，硼替佐米以剂量和时间依赖的方式在 HCC 细胞系（包括 Huh-7、Sk-Hep1 和 Hep3B）中激活自噬。硼替佐米以剂量和时间依赖的方式在所有测试的 HCC 细胞中下调 CIP2A、磷酸化 Akt（P-Akt）和磷酸化 4EBP1（P-4EBP1）。CIP2A 的异位表达消除了硼替佐米对自噬的影响。硼替佐米与 calyculin A（一种 PP2A 抑制剂）联合治疗降低了硼替佐米对 P-Akt、P-4EBP1 和自噬的作用。通过异位过表达增加 Akt 或 4EBP1 的磷酸化可保护细胞免受硼替佐米诱导的自噬。此外，我们研究了结构上与硼替佐米非常相似但无蛋白酶体活性的硼替佐米衍生物 ΔBtz 在 HCC 中的作用。有趣的是，ΔBtz 在自噬、CIP2A、P-Akt 和 P-4EBP1 方面表现出与硼替佐米相似的作用，表明硼替佐米对自噬的作用独立于蛋白酶体抑制。此外，我们的体内数据表明，硼替佐米和 ΔBtz 均抑制 Huh-7 肿瘤的生长，下调 CIP2A、P-Akt 并诱导自噬。总之，硼替佐米通过 CIP2A-PP2A-Akt-4EBP1 通路诱导 HCC 中的自噬。
