Role of cyclophilin B in prolactin signal transduction and nuclear retrotranslocation.
The pleiotropic actions of PRL are necessary for mammary growth and differentiation and in vitro lymphoid proliferation. The proximal action of this ligand is mediated by its cell surface receptor via associated networks. PRL action, however, is also associated with the internalization and translocation of this hormone into the nucleus. To delineate the mechanism of this retrotranslocation, a yeast two-hybrid screen was performed and revealed an interaction between PRL and cyclophilin B (CypB). CypB is a peptidyl prolyl isomerase (PPI) found in the endoplasmic reticulum, extracellular space, and nucleus. The interaction between CypB and PRL was subsequently confirmed in vitro and in vivo through the use of recombinant proteins and coimmunoprecipitation studies. The exogenous addition of CypB potentiated the 3H-thymidine incorporation of PRL-dependent cell lines up to 18-fold. CypB by itself was nonmitogenic and did not potentiate the action of GH or other interleukins. CypB did not alter the affinity of the PRL receptor (PRLr) for its ligand, or increase the phosphorylation of PRLr-associated Jak2 or Stat5a. The potentiation of PRL-action by CypB, however, was accompanied by a dramatic increase in the nuclear retrotranslocation of PRL. A CypB mutant, termed CypB-NT, was generated that lacked the wild-type N-terminal nuclear localization sequence. Although CypB-NT demonstrated levels of PRL binding and PPI activity equivalent to wild-type CypB, it was incapable of mediating the nuclear retrotranslocation of PRL or enhancing PRL-driven proliferation. These studies reveal CypB as an important chaperone facilitating the nuclear retrotransport and action of the lactogenic hormones.
Department of Pathology and Laboratory Medicine, University of Pennsylvania Medical Center, Philadelphia 19104, USA.
M A
MA
Rycyzyn
S C
SC
Reilly
K
K
O'Malley
C V
CV
Clevenger
D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D000818:Animals; D001483:Base Sequence; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D021983:Cyclophilins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism; D013006:Growth Hormone / Q000494:pharmacology; D006801:Humans; D007376:Interleukin-2 / Q000494:pharmacology; D007377:Interleukin-3 / Q000494:pharmacology; D053614:Janus Kinase 2; D008894:Milk Proteins; D008969:Molecular Sequence Data; D019696:Peptidylprolyl Isomerase; D010766:Phosphorylation; D011388:Prolactin / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D051381:Rats; D011981:Receptors, Prolactin / Q000378:metabolism; D050799:STAT5 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
D004268:DNA-Binding Proteins; D007376:Interleukin-2; D007377:Interleukin-3; D008894:Milk Proteins; D011518:Proto-Oncogene Proteins; D011981:Receptors, Prolactin; D050799:STAT5 Transcription Factor; C494092:STAT5A protein, human; C494094:Stat5a protein, rat; D015534:Trans-Activators; D025521:Tumor Suppressor Proteins; C081786:cyclophilin B; D011388:Prolactin; D013006:Growth Hormone; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; C507927:Jak2 protein, rat; D053614:Janus Kinase 2; D021983:Cyclophilins; D019696:Peptidylprolyl Isomerase