Suppression of apoptosis following hormone-retractory prostate cancer.

肾细胞癌是一种独特的实体瘤，即使在晚期也偶尔会出现自发消退，其潜在机制尚不清楚。为了探讨促凋亡分子caspase-1在肾癌生长调控中的潜在作用，我们从小鼠肾癌细胞系Renca中建立了外源性caspase-1的表达载体。在体外，caspase-1的过表达不会影响Renca细胞在指数期的生长，但会在50-75%融合时诱导细胞死亡，而对照组细胞只有在达到100%融合时才发生凋亡。当移植到同基因BALB/c小鼠的侧翼时，过表达caspase-1的Renca细胞不能有效地建立实体瘤的生长，仅在11只动物中有7只(41%)形成可测量的肿瘤，而对照细胞在6只动物中形成肿瘤(100%)。Caspase-1高表达细胞形成的肿瘤在直径达到5~10 mm后生长明显减慢，组织学检查发现大量TUNEL染色阳性的凋亡细胞。有趣的是，在对照细胞的肿瘤中没有检测到内源性caspase-1，当重新培养并暴露于去甲基化试剂5-aza-2‘-deoxcytidine时，这些对照细胞重新表达caspase-1。此外，用5-氮杂-2‘-脱氧胞苷处理人肾癌DELL系ACHN后，caspase-1的表达也恢复了，这在治疗前没有检测到。这些数据表明，通过DNA甲基化沉默caspase-1可能参与了一些作为实体瘤生长的肾细胞癌的发生。

Renal cell cancer is a unique solid tumor which occasionally shows spontaneous regression even at an advanced stage, of which underlying mechanism is not well understood. To investigate a potential role of a pro-apoptotic molecule caspase-1 in the growth regulation of renal cell cancer, we created transfectants expressing exogenous caspase-1 from a murine renal cancer cell line Renca Overexpression of caspase-1 did not affect growth of Renca cells in vitro at their exponential phase, but induced apoptotic cell death at 50-75% confluence, while control bells underwent apoptosis only after reaching 100% confluence. When implanted to the flank of a syngeneic BALB/c mouse, caspase-1 overexpressing Renca cells did not effectively establish growth as a solid tumor, forming a measurable tumor in only 7 of 11 (41%) animals, while control cells formed a tumor in 6 of 6 (100%) animals. The growth of tumors from caspase-1 overexpressing cells markedly slowed down after reaching 5-10 mm in diameter, and histological examination of such tumors revealed numerous apoptotic cells positively stained by TUNEL assay. Interestingly, endogenous caspase-1 was not detected in the tumors from control cells, which re-expressed caspase-1 when re-cultured and exposed to a demethylation reagent 5-aza-2'-deoxycytidine. Furthermore, treatment of a human renal cancer dell line ACHN with 5-aza-2'-deoxycytidine also recovered caspase-1 expression, which was not detected before treatment. These data suggest that silencing of caspase-1 through DNA methylation may be involved in the oncogenesis of some renal cell cancers growing as a solid tumor.