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Mol Cell Biol, February 1998, p. 896-905, Vol. 18, No. 2
Department of Pathology and Laboratory
Medicine, University of Pennsylvania Medical Center, Philadelphia,
Pennsylvania 19104
Received 24 July 1997/Returned for modification 10 September
1997/Accepted 19 November 1997
The intracellular domain of the prolactin (PRL) receptor (PRLr) is
required for PRL-induced signaling and proliferation. To identify and
test the functional stoichiometry of those PRLr motifs required for
transduction and growth, chimeras consisting of the extracellular
domain of either the
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Copyright © 1998, American Society for Microbiology. All rights reserved.
Stoichiometric Structure-Function Analysis of the
Prolactin Receptor Signaling Domain by Receptor Chimeras
or
subunit of human granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor (GM-CSFr) and the intracellular domain of the rat PRLr were synthesized. Because the
high-affinity binding of GM-CSF results from the specific pairing of
one
- and one
-GM-CSFr, use of GM-CSFr/PRLr chimera enabled
targeted dimerization of the PRLr intracellular domain. To that end,
the extracellular domains of the
- and
-GM-CSFr were conjugated
to one of the following mutations: (i) PRLr C-terminal truncations,
termed
278,
294,
300,
322, or
322; (ii) PRLr tyrosine
replacements, termed Y309F, Y382F, or Y309+382F; or, (iii) PRLr
wild-type short, intermediate, or long isoforms. These chimeras were
cotransfected into the cytokine-responsive Ba/F3 line, and their
expression was confirmed by ligand binding and Northern and Western
blot analyses. Data from these studies revealed that heterodimeric
complexes of the wild type with C-terminal truncation mutants of the
PRLr intracellular domain were incapable of ligand-induced signaling or
proliferation. Replacement of any single tyrosine residue (Y309F or
Y382F) in the dimerized PRLr complex resulted in a moderate reduction
of receptor-associated Jak2 activation and proliferation. In contrast,
trans replacement of these residues (i.e.,
Y309F and
Y382F) markedly reduced ligand-driven Jak2 activation and
proliferation, while cis replacement of both tyrosine
residues in a single intracellular domain (i.e.,
Y309+382F) produced
an inactive signaling complex. Analysis of these GM-CSFr-PRLr complexes revealed equivalent levels of Jak2 in association with the
mutant receptor chains, suggesting that the tyrosine residues at 309 and 382 do not contribute to Jak association, but instead to its
activation. Heterodimeric pairings of the intracellular domains from
the known PRLr receptor isoforms (short-intermediate, short-long, and
intermediate-long) also yielded inactive receptor complexes. These data
demonstrate that the tyrosine residues at 309 and 382, as well as
additional residues within the C terminus of the dimerized PRLr
complex, contribute to PRL-driven signaling and proliferation.
Furthermore, these findings indicate a functional requirement for the
pairing of Y309 and Y382 in trans within the dimerized
receptor complex.
*
Corresponding author. Mailing address: Department of
Pathology and Laboratory Medicine, University of Pennsylvania Medical Center, 509 S-C Labs, 422 Curie Blvd., Philadelphia, PA 19104. Phone:
(215) 898-0734. Fax: (215) 573-8944. E-mail:
clevengc{at}mail.med.upenn.edu.
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