Labdane type diterpenes down-regulate the expression of c-Myc protein, butnot of Bcl-2, in human leukemia T-cells undergoing apoptosis

Sclareol (1) and ent-3 beta -hydroxy-13-epi-manoyl oxide (2) belong to the labdane type diterpenes. They were isolated from the leaves and from the fr uits of Cistus creticus subsp. creticus, and were found to be active agains t human leukemic cell lines. Compound 2 was converted to its thiomidazolide derivative (3). Compounds I and 3 were found to induce apoptotic cell deat h in human T cell leukemia lines and to interfere with their cell cycle, ar resting cells at G(0/1) phase. Apoptosis can involve the activation and/or suppression of critical genes such as c-myc whose reduction or its inapprop riate expression can be associated with induction of cell death and bcl-2 w hose activation prevents apoptosis in the latter case. In order to detect a ny concomitant effect (1 and 3) upon c-myc and bcl-2 oncogene expression, w e performed Western blot analysis to determine the levels of expression of these two genes upon treatment with the above compounds. Western blot analy sis showed that of c-myc proto-oncogene levels were markedly reduced before massive apoptosis ensued in H33AJ-JA1 and MOLT3 cells, while bcl-2 express ion remained unaffected. Thus, induction of apoptosis due to compounds I an d 3 in these T cell leukemic cell lines is preceded by c-myc down regulatio n and furthermore sustained bcl-2 expression does not rescue cells from apo ptosis under the conditions used. (C) 2001 Elsevier Science Ltd. All rights reserved.