Department of Surgery, Jefferson Pancreas, Biliary and Related Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania, United States of America.
PLoS One. 2010 Nov 29;5(11):e15455. doi: 10.1371/journal.pone.0015455.
The expression of protein phosphatase 32 (PP32, ANP32A) is low in poorly differentiated pancreatic cancers and is linked to the levels of HuR (ELAV1), a predictive marker for gemcitabine response. In pancreatic cancer cells, exogenous overexpression of pp32 inhibited cell growth, supporting its long-recognized role as a tumor suppressor in pancreatic cancer. In chemotherapeutic sensitivity screening assays, cells overexpressing pp32 were selectively resistant to the nucleoside analogs gemcitabine and cytarabine (ARA-C), but were sensitized to 5-fluorouracil; conversely, silencing pp32 in pancreatic cancer cells enhanced gemcitabine sensitivity. The cytoplasmic levels of pp32 increased after cancer cells are treated with certain stressors, including gemcitabine. pp32 overexpression reduced the association of HuR with the mRNA encoding the gemcitabine-metabolizing enzyme deoxycytidine kinase (dCK), causing a significant reduction in dCK protein levels. Similarly, ectopic pp32 expression caused a reduction in HuR binding of mRNAs encoding tumor-promoting proteins (e.g., VEGF and HuR), while silencing pp32 dramatically enhanced the binding of these mRNA targets. Low pp32 nuclear expression correlated with high-grade tumors and the presence of lymph node metastasis, as compared to patients' tumors with high nuclear pp32 expression. Although pp32 expression levels did not enhance the predictive power of cytoplasmic HuR status, nuclear pp32 levels and cytoplasmic HuR levels associated significantly in patient samples. Thus, we provide novel evidence that the tumor suppressor function of pp32 can be attributed to its ability to disrupt HuR binding to target mRNAs encoding key proteins for cancer cell survival and drug efficacy.
蛋白磷酸酶 32（PP32，ANP32A）在低分化胰腺癌中的表达较低，与 HuR（ELAV1）水平相关，HuR 是吉西他滨反应的预测标志物。在胰腺癌细胞中，pp32 的外源性过表达抑制细胞生长，支持其作为胰腺癌肿瘤抑制因子的长期公认作用。在化疗敏感性筛选试验中，过表达 pp32 的细胞对核苷类似物吉西他滨和阿糖胞苷（ARA-C）具有选择性耐药性，但对 5-氟尿嘧啶敏感；相反，沉默胰腺癌细胞中的 pp32 增强了吉西他滨的敏感性。癌细胞用某些应激源（包括吉西他滨）处理后，pp32 的细胞质水平增加。pp32 过表达减少了 HuR 与编码吉西他滨代谢酶脱氧胞苷激酶（dCK）的 mRNA 的结合，导致 dCK 蛋白水平显著降低。同样，异位 pp32 表达导致 HuR 与促进肿瘤的蛋白（如 VEGF 和 HuR）的 mRNA 结合减少，而沉默 pp32 则显著增强了这些 mRNA 靶标的结合。与核内 pp32 高表达的患者肿瘤相比，核内 pp32 低表达与高级别肿瘤和淋巴结转移的存在相关。尽管 pp32 表达水平并未增强细胞质 HuR 状态的预测能力，但在患者样本中，核内 pp32 水平和细胞质 HuR 水平显著相关。因此，我们提供了新的证据表明，pp32 的肿瘤抑制功能可归因于其破坏 HuR 与编码癌症细胞存活和药物疗效的关键蛋白的靶 mRNA 结合的能力。
