Suppression of apoptosis following hormone-retractory prostate cancer.

肾细胞癌是一种独特的实体瘤，即使在晚期也偶尔显示自发消退，其潜在机制尚不清楚。为了研究促凋亡分子caspase-1在肾细胞癌生长调节中的潜在作用，我们从鼠肾癌细胞系Renca中创建了表达外源性caspase-1的转染子。caspase-1的过表达在体外不影响处于指数期的Renca细胞的生长，但在50-75%汇合时诱导凋亡性细胞死亡，而对照钟细胞仅在达到100%融合后才发生凋亡。当植入同基因BALB/c小鼠的侧腹时，过表达caspase-1的Renca细胞没有有效地建立实体瘤生长，仅在11只动物中的7只（41%）中形成可测量的肿瘤，而对照细胞在6只动物中形成肿瘤（100%）。caspase-1过表达细胞的肿瘤生长在直径达到5-10 mm后明显减慢，并且这种肿瘤的组织学检查显示大量凋亡细胞通过TUNEL测定呈阳性染色。有趣的是，在来自对照细胞的肿瘤中未检测到内源性半胱天冬酶-1，当再培养并暴露于去甲基化试剂5-氮杂-2 '-脱氧胞苷时，对照细胞重新表达半胱天冬酶-1。此外，用5-氮杂-2 '-脱氧胞苷治疗人肾癌细胞系ACHN也恢复了半胱天冬酶-1的表达，这在治疗前没有检测到。这些数据表明，通过DNA甲基化沉默半胱天冬酶-1可能参与一些肾细胞癌生长为实体瘤的肿瘤发生。

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.