Growth signaling and JAK2 association mediated by membrane-proximal cytoplasmic regions of prolactin receptors.
Prolactin (PRL) has recently been demonstrated to induce tyrosine phosphorylation and activation of the cytoplasmic tyrosine kinase JAK2 in PRL-dependent Nb2 lymphoma cells. The present study represents an initial effort to identify cytoplasmic regions of the PRL receptor (PRLR) that are critical to growth signal generation and JAK2 activation. Variably truncated rat PRLRs were stably expressed in the murine 32D cell line. PRL-induced proliferation was mediated by the full-length receptor and the mutant G328, which contains the membrane-proximal Homology Boxes 1 and 2 characteristic of hematopoietin receptors. In contrast, mutant receptors lacking either Box 2 or both Boxes 1 and 2 were not capable of transmitting a growth signal. The mitogenic capacity of the PRLR variants correlated with JAK2 association and activation, as well as with induction of mRNA levels for the growth-related gene ornithine decarboxylase. We conclude that mitogenic competence of rat PRLRs resides within the first 94 amino acids of the cytoplasmic domain. The data suggest that Homology Box 1/Box 2 region is critical to JAK2 phosphorylation and association with the PRLR. These findings will serve as a basis for more detailed molecular characterization of PRLR domains essential for JAK2 interaction and growth signal generation.
Biological Carcinogenesis and Development Program, Program Resources Inc./DynCorp, Frederick, Maryland.
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DaSilva
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Howard
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Rui
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Kirken
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Farrar
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002455:Cell Division / Q000187:drug effects*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D017931:DNA Primers; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D007377:Interleukin-3 / Q000494:pharmacology; D053614:Janus Kinase 2; D051379:Mice; D008969:Molecular Sequence Data; D016296:Mutagenesis; D009955:Ornithine Decarboxylase / Q000096:biosynthesis; D010957:Plasmids; D016133:Polymerase Chain Reaction; D011388:Prolactin / Q000494:pharmacology*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D011981:Receptors, Prolactin / Q000096:biosynthesis / Q000187:drug effects / Q000502:physiology*; D015183:Restriction Mapping; D017384:Sequence Deletion; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D015398:Signal Transduction; D014162:Transfection
D017931:DNA Primers; D007377:Interleukin-3; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D011981:Receptors, Prolactin; D011388:Prolactin; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; C507926:Jak2 protein, mouse; C507927:Jak2 protein, rat; D053614:Janus Kinase 2; D009955:Ornithine Decarboxylase