Leukemic cell-surface CD13/aminopeptidase N and resistance to apoptosis mediated by endothelial cells.
BACKGROUND
Attachment of leukemic cells to vascular endothelial cells induces the vascular endothelial cells to release endothelial cell-derived interleukin 8 (endothelial IL-8), which then induces leukemic cells to undergo apoptosis. NB4, a human promyelocytic leukemic cell line that expresses high levels of cell-surface CD13/aminopeptidase N, does not undergo endothelial IL-8-induced apoptosis. Consequently, we investigated the relationship between cell-surface aminopeptidase activity and endothelial IL-8 induction of apoptosis in various leukemic cell lines.


METHODS
CD13/aminopeptidase N activity and IL-8-induced apoptosis were examined in leukemic cell lines. Endothelial IL-8-induced apoptosis was examined further in NB4 cells, K562 cells (human chronic myelogenous leukemic cells expressing low levels of CD13/aminopeptidase N), CD13/aminopeptidase N-transfected K562 (K562/CD13) cells that overexpress aminopeptidase, and mock-transfected K562 cells (vector only). These cells were also cocultured with a vascular endothelial cell layer to investigate the association between aminopeptidase activity and apoptosis in this system. All statistical tests were two-sided.


RESULTS
Endothelial IL-8 induced apoptosis in K562 cells but not in K562/CD13 cells. A combination of an aminopeptidase inhibitor (such as bestatin) and endothelial IL-8 induced apoptosis in NB4 cells and K562/CD13 cells (2.88-fold difference [95% confidence interval [CI] = 1.82-fold to 3.94-fold], P =.004 for bestatin-treated NB4 cells and 4.31-fold difference [95% CI = 3.52-fold to 5.10-fold], P<.001 for bestatin-treated K562/CD13 cells). When aminopeptidase activity in NB4 cells was modulated by aminopeptidase inhibitors, a statistically significant correlation was found between aminopeptidase activity and the proportion of apoptotic cells induced by endothelial IL-8 (r = -.837, P<.001 by Pearson's correlation coefficient; r = -.697, P =.013 by Spearman's correlation analysis by ranks). K562/CD13 cells cocultured with vascular endothelial cells did not undergo apoptosis, but the addition of bestatin resulted in the induction of apoptosis in K562/CD13 cells (2.70-fold difference [95% CI = 1.77-fold to 3.63-fold], P<.001). Bestatin treatment increased the level of IL-8 mRNA in and the amount of IL-8 secreted by vascular endothelial cells.


CONCLUSIONS
High levels of cell-surface CD13/aminopeptidase N appear to allow leukemic cells to resist endothelial IL-8-induced apoptosis. The combination of endothelial IL-8 and bestatin induce leukemic cells expressing high levels of CD13/aminopeptidase N to undergo apoptosis. Bestatin may be useful for treating patients with leukemia.
Mishima
Yuji
Y
Biochemical Research Laboratory, Morinaga Milk Industry Co. Ltd., Kanagawa, Japan.
Matsumoto-Mishima
Yuko
Y
Terui
Yasuhito
Y
Katsuyama
Misa
M
Yamada
Muneo
M
Mori
Masaki
M
Ishizaka
Yukihito
Y
Ikeda
Kazuma
K
Watanabe
Jun-ichiro
J
Mizunuma
Nobuyuki
N
Hayasawa
Hirotoshi
H
Hatake
Kiyohiko
K
D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D015152:Blotting, Northern; D018826:CD13 Antigens / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000502:physiology*; D005455:Fluorescent Antibody Technique; D006801:Humans; D020287:In Situ Nick-End Labeling; D016209:Interleukin-8 / Q000378:metabolism* / Q000494:pharmacology / Q000502:physiology*; D020014:K562 Cells / Q000473:pathology; D007930:Leucine / Q000031:analogs & derivatives* / Q000494:pharmacology; D007938:Leukemia / Q000473:pathology*; D014162:Transfection; D014471:Umbilical Veins
D000903:Antibiotics, Antineoplastic; D016209:Interleukin-8; D018826:CD13 Antigens; D007930:Leucine; C012211:ubenimex