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Downregulation of topoisomerase I in differentiating human intestinal epithelial cells
Author(s) -
Ulukan Hulya,
Muller Mark T.,
Swaan Peter W.
Publication year - 2001
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/ijc.1463
Subject(s) - downregulation and upregulation , topoisomerase , microbiology and biotechnology , cancer research , biology , pathology , medicine , enzyme , gene , genetics , biochemistry
To better understand the increased sensitivity of proliferating intestinal epithelial cells to topoisomerase I (topo I) poisons, we examined differentiation of a human intestinal cell line (Caco‐2) in the presence of camptothecin (CPT) and its analogs irinotecan (CPT‐11) and topotecan (TPT). The prodrug CPT‐11 exerts its antitumor activity after transformation to SN‐38. We show that cleavable complex formation in vivo (on genomic DNA) induced by CPT or SN‐38 is 4‐ to 7‐fold reduced in fully differentiated cells relative to undifferentiated cells. TPT‐induced cleavable complexes, however, are reduced by 30‐fold. In contrast, CPT‐11‐driven cleavable complexes did not change during cell differentiation. In general, cytotoxicity closely paralleled cleavable complex formation, as attested to by the four‐ to 6‐fold decrease in cytotoxicity in fully differentiated cells treated with CPT and SN‐38 compared with proliferating cells. Topo I activity and polypeptide levels decreased 4‐fold over the course of differentiation. This reduction occurs as Caco‐2 cells approach G 1 and simultaneously differentiate. In contrast, human diploid fibroblasts do not show a reduction in topo I when entering G 1 ; therefore, topo I downregulation is a differentiation‐specific event in the Caco‐2 cell line. Cleavable complex formation and cytotoxicity induced by CPT and SN‐38 correlate with topo I level and activity in cells at different stages in their differentiation. Thus, high target levels correspond closely with drug sensitivity and since proliferating cells contain larger amounts of topo I, we conclude that epithelial crypt cells probably succumb to chemotherapy involving topo I poisons. © 2001 Wiley‐Liss, Inc.