Hypersensitivity of NIH3T3 cells transformed by H-RAS gene to DNA-topoisomerase-I inhibitors

✍ Scribed by Tatsuo Ohira; Kazuto Nishio; Fumihiko Kanzawa; Tomoyuki Ishida; Yuichiro Ohe; Hitoshi Arioka; Yasunori Funayama; Hayato Ogasawara; Harubumi Kato; Nagahiro Saijo

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: French
• Weight: 736 KB
• Volume: 67
• Category: Article
• ISSN: 0020-7136
• DOI: 10.1002/(sici)1097-0215(19960904)67:5<702::aid-ijc19>3.0.co;2-6

✦ Synopsis

We examined the effects of the introduction of H-ras oncogene into murine cell line NIH3T3 on growth inhibition by topoisomerase-I (topo-I) inhibitors. The H-ras-transformed cells (pT22-3) showed approximately I 2-fold increased sensitivity to a novel topo-l inhibitor, NB-506 [6-N-formylamino-I2,I3dihydro-I, I I -dihydroxy-I3-(p-D -glucopyranosyl)-5H-indolo(2,3a)pyrrolo(3,4-c) carbazole-5,7(6H)-dione], compared with the parental NIH3T3 cells. pT22-3 also showed increased sensitivity to other topo-l inhibitors such as camptothecin (approx. 3.0fold) and CPT-I I (irinotecan, approx. 3.0-fold). Transformation of NIH3T3 by another oncogene (erbB2) did not affect their sensitivity to these topo-l inhibitors. pT22-3 had approximately 32-fold higher topo-l activity than NIH3T3, but the same topo-l content. In a cell-free system, topo-l activity was increased 2-fold by addition of the H-ras protein precipitated from pT22-3 cells. Top0 I in the nuclear extract of pT22-3 was eluted easily by low concentrations of NaCl compared with that of NIH3T3, suggesting a qualitative change in pT22-3 top0 1. Increased phosphorylation of top0 I was observed in pT22-3. Furthermore, NB-506 decreased the amount of the GTP-bound form of the H-ras product in pT22-3 cells. These results suggest that the high growth-inhibitory effect of a topo-l inhibitor, NB-506, on H-ras-transformed NIH3T3 cells is due to the H-ras-mediated signal-transduction pathway.