10997587

pubmed:Citation

1

The functional role of the cyclin-dependent kinase inhibitor (CDKI) p21CIP1 in differentiation of human myelomonocytic leukemia cells (U937) exposed to low concentrations of the antimetabolite 1-beta-D-arabino-furanosylcytosine (ara-C) was examined utilizing a cell line stably expressing a p21CIP1 antisense construct. Continuous exposure to 50 nM ara-C led to marked induction of p21CIP1 at 48-72 h in empty-vector control cells but not in their antisense-expressing counterparts (p21AS/F4 and B8). Such treatment induced expression of the myelomonocytic differentiation marker CD11b in approximately 35% of control cells, but no evidence of maturation was noted in antisense-expressing lines. However, antisense-expressing cells exposed to low concentrations of ara-C exhibited a reciprocal increase in apoptosis, manifested by the appearance of cells with classic morphologic features and hypodiploid quantities of DNA, reduced mitochondrial membrane potential (deltapsim), an increase in cytochrome c release into the cytosol, cleavage/activation of procaspases-9 and -3, and degradation of PARP and p27Kip1. Whereas empty-vector control cells exposed to 50 nM ara-C exhibited a decline in Bcl-2 expression, dephosphorylation of pRb, and an initial accumulation in S-phase, antisense-expressing cells did not. However, c-Myc down-regulation induced by low concentrations of ara-C was, if anything, more complete in antisense-expressing cells. Exposure of control but not antisense-expressing cells to ara-C led to phosphorylation/activation of MAP kinase at 24 h; moreover, the specific MEK/MAP kinase inhibitor PD98059 enhanced low-dose ara-C-mediated apoptosis only in wild-type cells. Lastly, exposure to 50 nM ara-C for 72 h resulted in detectable levels of cytoplasmic p21CIP1, a phenomenon associated with resistance to apoptosis, only in empty vector controls. Collectively, these findings demonstrate a functional role for p21CIP1 in leukemic cell maturation induced by low concentrations of ara-C. They also indicate that, as in the case of more conventional differentiation-inducers such as phorbol esters, disruption of the p21CIP1 response after exposure to low concentrations of the cytotoxic drug ara-C prevents leukemic cells from engaging a maturation program, but instead directs them along an apoptotic pathway.

eng

IM

MEDLINE

0301-4681

Print

NLM

1-13

pubmed-meshheading:10997587-Apoptosis, pubmed-meshheading:10997587-Cell Cycle, pubmed-meshheading:10997587-Cell Differentiation, pubmed-meshheading:10997587-Cell Division, pubmed-meshheading:10997587-Cyclin-Dependent Kinase Inhibitor p21, pubmed-meshheading:10997587-Cyclin-Dependent Kinases, pubmed-meshheading:10997587-Cyclins, pubmed-meshheading:10997587-Cytarabine, pubmed-meshheading:10997587-Gene Expression Regulation, Neoplastic, pubmed-meshheading:10997587-Histocytochemistry, pubmed-meshheading:10997587-Humans, pubmed-meshheading:10997587-Leukemia, Myeloid, pubmed-meshheading:10997587-Macrophage-1 Antigen, pubmed-meshheading:10997587-Mitogen-Activated Protein Kinases, pubmed-meshheading:10997587-Neoplasm Proteins, pubmed-meshheading:10997587-Oligonucleotides, Antisense, pubmed-meshheading:10997587-Phosphorylation, pubmed-meshheading:10997587-Proto-Oncogene Proteins c-myc, pubmed-meshheading:10997587-Retinoblastoma Protein, pubmed-meshheading:10997587-U937 Cells

Evidence of a functional role for the cyclin-dependent kinase inhibitor p21CIP1 in leukemic cell (U937) differentiation induced by low concentrations of 1-beta-D-arabinofuranosylcytosine.

Journal Article, Research Support, U.S. Gov't, P.H.S., Research Support, U.S. Gov't, Non-P.H.S., Research Support, Non-U.S. Gov't