Hammerhead ribozyme-mediated cleavage of the human insulin-like growth factor-II ribonucleic acid in vitro and in prostate cancer cells

Insulin-like growth factor (IGF)-II plays an important role in fetal growth and development. IGFs are potent mitogens for a variety of cancer cells. A paracrine/autocrine role of TGF-II in the growth of breast and prostate ca ncer cells has been suggested. To test the role of IGF-II in cancer cell gr owth, hammerhead ribozymes targeted to human IGF-II RNA were constructed. S ingle (R)- and double (RR)-ribozymes were catalytically active in vitro whe reas mutant ribozymes (Ai or MM) did not cleave IGF-II RNA. RR was more act ive than R. In human prostate cancer PC-3 cells, both R and RR similarly su ppressed IGF-II messenger RNA (mRNA) levels (similar to 40%) compared with the level in parental or M-expressing PC-3 cells. Polymerase II and III pro moter-driven R similarly suppressed IGF-II mRNA levels. Suppression of IGF- II mRNA levels by R was associated with suppression of IGF-II protein level s. R- (or RR-) expressing PC-3 cells did not grow under serum-starved condi tions and showed prolonged doubling times in the presence of 10% FCS compar ed with those of parental or M-expressing cells. These results substantiate d that IGF-II plays a critical role in prostate cancer cell growth.