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Molecular and Cellular Biology, February 1999, p. 1171-1181, Vol. 19, No. 2
Laboratory of Molecular Oncology, The
Rockefeller University, New York, New York 10021
Received 9 June 1998/Returned for modification 5 August
1998/Accepted 3 November 1998
The c-Mer receptor tyrosine kinase (RTK) is most closely related to
chicken c-Eyk and belongs to the Axl RTK subfamily. Although not
detected in normal lymphocytes, c-Mer is expressed in B- and T-cell
leukemia cell lines, suggesting an association with lymphoid malignancies. To gain an understanding of the role of this receptor in
lymphoid cells, we expressed in murine interleukin-3 (IL-3)-dependent Ba/F3 pro-B-lymphocyte cells a constitutively active receptor, CDMer,
formed from the CD8 extracellular domain and the c-Mer intracellular
domain. Cells transfected with a plasmid encoding the CDMer receptor
became IL-3 independent. When tyrosine (Y)-to-phenylalanine (F)
mutations were introduced into c-Mer, only the Y867 change significantly reduced the IL-3-independent cell proliferation. The Y867
residue in the CDMer receptor mediated the binding of Grb2, which
recruited the p85 phosphatidylinositol 3-kinase (PI 3-kinase). Despite
the difference in promotion of proliferation, both the CDMer and mutant
F867 receptors activated Erk in transfected cells. On the other hand,
we found that both transcriptional activation of NF-
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Biological Effects of c-Mer Receptor Tyrosine
Kinase in Hematopoietic Cells Depend on the Grb2 Binding Site in the
Receptor and Activation of NF-
B
B and activation
of PI 3-kinase were significantly suppressed with the F867 mutant
receptor, suggesting that the activation of antiapoptotic pathways is
the major mechanism for the observed phenotypic difference. Consistent
with this notion, apoptosis induced by IL-3 withdrawal was strongly
prevented by CDMer but not by the F867 mutant receptor.
*
Corresponding author. Mailing address: The Rockefeller
University, Box 169, 1230 York Ave., New York, NY 10021. Phone: (212) 327-8802. Fax: (212) 327-7943. E-mail:
saburo{at}rockvax.rockefeller.edu.
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