Suppression of oncogenic transformation by hypothemycin associated with accelerated cyclin D1 degradation through ubiquitin-proteasome pathway.
Hypothemycin was originally isolated as an antifungal metabolite of Hypomyces trichothecoides. Here we report that treatment on v-K-ras-transformed NIH3T3 cells (DT cells) with hypothemycin caused drastic decrease in amount of cyclin D1 protein with concomitant prolongation of G1 phase in their cell cycle. Analysis using hypothemycin-resistant mutant of Schizosaccharomyces pombe (S. pombe) was carried out to show that S. pombe rhp6+ (homologue of Saccharomyces cerevisiae RAD6) and mammalian ubiquitin-conjugating enzyme 2 (ubc2) are the targets of hypothemycin or its downstream molecules in ubiquitin-conjugation process. Furthermore, in the presence of lactacystin, a specific inhibitor for proteasome, hypothemycin greatly enhanced the accumulation of multi-ubiquitinated form of cyclin D1 in DT cells. Therefore, it is indicated that hypothemycin facilitates ubiquitinating process of cyclin D1. In terms of malignant phenotype, hypothemycin inhibited anchorage-independent growth and reverted the morphology of DT cells. On the contrary, their morphology still remained transformed in the additional presence of lactacystin. Our results suggest that cyclin D1 is a key molecule working downstream in ras-signaling and that the transformation can be inhibited by the compound which can activate ubiquitin-proteasome pathway including degradation of cyclin D1.
Shionogi Research Laboratories, Shionogi & Co., Ltd., Osaka, Japan. hikaru.sonoda@shionogi.co.jp
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Sonoda
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Omi
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Hojo
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Nishida
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Omura
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Sugita
D016475:3T3 Cells; D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D000970:Antineoplastic Agents / Q000302:isolation & purification / Q000494:pharmacology*; D015153:Blotting, Western; D002461:Cell Line, Transformed; D002471:Cell Transformation, Neoplastic / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D019938:Cyclin D1 / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D018076:DNA, Complementary / Q000096:biosynthesis / Q000302:isolation & purification; D015536:Down-Regulation; D016193:G1 Phase / Q000187:drug effects; D051379:Mice; D003904:Mitosporic Fungi / Q000737:chemistry; D009097:Multienzyme Complexes / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D012097:Repressor Proteins / Q000235:genetics; D012568:Schizosaccharomyces / Q000201:enzymology; D014452:Ubiquitins / Q000235:genetics / Q000378:metabolism*; D015025:Zearalenone / Q000031:analogs & derivatives
D000970:Antineoplastic Agents; D018076:DNA, Complementary; D009097:Multienzyme Complexes; D012097:Repressor Proteins; D014452:Ubiquitins; C120440:hypothemycin; C067713:lactacystin; D019938:Cyclin D1; D015025:Zearalenone; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000111:Acetylcysteine