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Charles V Clevenger

Publications and source records attributed to Charles V Clevenger.

10 recordsLinked to original sources
PubMed2006

Ligand-independent dimerization of the human prolactin receptor isoforms: functional implications.

Prolactin (PRL) contributes to the growth of normal and malignant breast tissues. PRL initiates signaling by engaging the PRL receptor (PRLr), a transmembrane (TM) receptor belonging to the cytokine receptor family. The accepted view has been that PRL activates the PRLr by inducing dimerization of the receptor, but recent reports show ligand-independent dimerization of other cytokine receptors. Using coimmunoprecipitation assays, we have confirmed ligand-independent dimerization of the PRLr in T47D breast cancer and HepG2 liver carcinoma cells. In addition, mammalian cells transfected with differentially epitope-tagged isoforms of the PRLr indicated that long, intermediate, and DeltaS1 PRLrs dimerized in a ligand-independent manner. To determine the domain(s) involved in PRLr ligand-independent dimerization, we generated PRLr constructs as follows: (1) the TM-ICD, which consisted of the TM domain and the intracellular domain (ICD) but lacked the extracellular domain (ECD), and (2) the ECD-TM, which consisted of the TM domain and the ECD but lacked the ICD. These constructs dimerized in a ligand-independent manner in mammalian cells, implicating a significant role for the TM domain in this process. These truncated PRLrs were functionally inert alone or in combination in cells lacking the PRLr. However, when introduced into cells containing endogenous PRLr, the ECD-TM inhibited human PRLr signaling, whereas the TM-ICD potentiated human PRLr signaling. These studies indicate that the ECD-TM and the TM-ICD are capable of modulating PRLr function. We also demonstrated an endogenous TM-ICD in T47D cells, suggesting that these findings are relevant to PRL-signaling pathways in breast cancer.

Animals↗
PubMed2004

Novel association of Vav2 and Nek3 modulates signaling through the human prolactin receptor.

Prolactin (PRL) receptor activation contributes to the progression and motility of human breast cancer. This event activates multimeric signaling pathways, including the activation of the Vav family of guanine nucleotide exchange factors. To detect novel proteins interacting with Vav, yeast two-hybrid analysis was performed and demonstrated an interaction between the serine/threonine NIMA (never in mitosis A)-related family kinase p56Nek3 and Vav1. The PRL-dependent interaction of Nek3 with Vav1 and Vav2 was confirmed by coimmunoprecipitation analysis. PRL stimulation of T47D cells induced Nek3 kinase activity and the interaction of Vav2/Nek3 with the PRL receptor. Increased Nek3 levels up-regulated Vav2 serine and tyrosine phosphorylation, whereas knockdown of Nek3 resulted in a reduction of Vav2 phosphorylation. Activation of guanosine triphosphatase Rac-1 in Chinese hamster ovary transfectants required both Nek3 and Vav2 and was inhibited by the overexpression of a kinase inactivating Nek3 mutant. However, overexpression of either Nek3 or kinase-inactive Nek3 had no effect on Vav2-potentiated signal transducer and activator of transcription 5-mediated gene expression. Overexpression of kinase inactive Nek3 in T47D cells led to a 50% increase in apoptosis vs. controls. These data suggest that the PRL-mediated activation of Nek3 contributes differentially to Vav2 signaling pathways involving Rac1 and signal transducer and activator of transcription 5 and implicates Nek3 during PRL-mediated actions in breast cancer.

Animals↗
PubMed2004

Roles and regulation of stat family transcription factors in human breast cancer.

Stats (for signal transducers and activators of transcription) are a family of transcription factors that regulate cell growth and differentiation. Their activity is latent until phosphorylation by receptor-associated kinases. A sizable body of data from cell lines, mouse models, and human tissues now implicates these transcription factors in the oncogenesis of breast cancer. Because Stat activity is modulated by several posttranslational modifications and protein-protein interactions, these transcription factors are capable of integrating inputs from multiple signaling networks. Given this, the future utilization of Stats as prognostic markers and therapeutic targets in human breast cancer appears likely.

Amino Acid Motifs↗
PubMed2003

Nuclear localization and function of polypeptide ligands and their receptors: a new paradigm for hormone specificity within the mammary gland?

The specific effects triggered by polypeptide hormone/growth factor stimulation of mammary cells were considered mediated solely by receptor-associated signaling networks. A compelling body of new data, however, clearly indicates that polypeptide ligands and/or their receptors are transported into the nucleus, where they function directly to regulate the expression of specific transcription factors and gene loci. The intranuclear function of these complexes may contribute to the explicit functions associated with a given ligand, and may serve as new targets for pharmacologic intervention.

Breast↗
PubMed2003

The role of prolactin in mammary carcinoma.

The contribution of prolactin (PRL) to the pathogenesis and progression of human breast cancer at the cellular, transgenic, and epidemiological levels is increasingly appreciated. Acting at the endocrine and autocrine/paracrine levels, PRL functions to stimulate the growth and motility of human breast cancer cells. The actions of this ligand are mediated by at least six recognized PRL receptor isoforms found on, or secreted by, human breast epithelium. The PRL/PRL receptor complex associates with and activates several signaling networks that are shared with other members of the cytokine receptor superfamily. Coupled with the recently identified intranuclear function of PRL, these networks are integrated into the in vitro and in vivo actions induced by ligand. These findings indicate that antagonists of PRL/PRL receptor interaction or PRL receptor-associated signal transduction may be of considerable utility in the treatment of human breast cancer.

Animals↗
PubMed2003

Role of prolactin/prolactin receptor signaling in human breast cancer.

Prolactin (PRL), a hormone utilized at both the endocrine and autocrine levels, stimulates breast epithelial growth, differentiation, and motility. Recent data at the cellular, epidemiologic, and genetic levels have implicated a significant role for this hormone in the pathogenesis of human breast cancer. A family of prolactin receptor (PRLr) isoforms mediates the effects of PRL in human tissue. Now numbering six, these isoforms are co-variably expressed to differing degrees in normal versus malignant tissues. Following ligand binding, proximal PRLr signaling is initiated by three tyrosine kinases, namely Jak2, Src, and Tec. Activation of these kinases results in the triggering of multiple signaling networks, many of which are integrated by the Stat5 transcription factor. Both tyrosine and serine phosphorylation regulate Stat5 activity, as does the interaction of this transcription factor with co-activators and -repressors within the nucleus. Recently our lab has discovered that Stat5 activity is also regulated by its direct interaction with the retrotranslocated complex of PRL and the peptidyl prolyl isomerase cyclophilin B. This interaction results in the release of a repressor of Stat5 DNA-binding, the Peptide Inhibitor of Activated Stat 3 (PIAS3). Taken together, these data suggest that the summated genomic and non-genomic signaling actions of the PRL/PRLr complex serve to trigger an orchestrated pattern of gene expression that contributes to mammary development and the pathobiology of breast cancer.

Journal Article↗
PubMed2002

The intranuclear prolactin/cyclophilin B complex as a transcriptional inducer.

The nuclear translocation of peptide hormones, such as the somatolactogenic hormone prolactin, after receptor internalization has been widely reported. Prolactin has been demonstrated to interact with cyclophilin B, a member of the immunophilin family of proteins. Cyclophilin B interaction with prolactin potentiated prolactin-induced proliferation, cell growth, and the nuclear retrotransport of prolactin. These effects could be abrogated by the removal of the peptidyl-prolyl isomerase activity of cyclophilin B. Our findings indicate that the intranuclear prolactin/cyclophilin B complex acts as a transcriptional inducer by interacting directly with Stat5, resulting in the removal of the Stat-repressor protein inhibitor of activated Stat 3 (PIAS3), thereby enhancing Stat5 DNA-binding activity and prolactin-induced, Stat5-mediated gene expression.

Animals↗
PubMed2002

Characterization of a novel and functional human prolactin receptor isoform (deltaS1PRLr) containing only one extracellular fibronectin-like domain.

Prolactin (PRL)-dependent signaling occurs as the result of ligand-induced homodimerization of the PRL receptor (PRLr). To date, short, intermediate, and long human PRLr isoforms have been characterized. To investigate the expression of other possible human PRLr isoforms, RT-PCR was performed on mRNA isolated from the breast carcinoma cell line T47D. A 1.5-kb PCR fragment was isolated, subcloned, and sequenced. The PCR product exhibited a nucleotide sequence 100% homologous to the human long isoform except bp 71-373 were deleted, which code for the S1 motif of the extracellular domain. Therefore, this isoform was designated the deltaS1 PRLr. Northern analysis revealed variable deltaS1 PRLr mRNA expression in a variety of tissues. Transfection of Chinese hamster ovary cells with deltaS1 cDNA showed the isoform is expressed at the protein level on the cell surface with a molecular mass of approximately 70 kDa. Kinetic studies indicated the deltaS1 isoform bound ligand at a lower affinity than wild-type receptor. The deltaS1 PRLr was also shown to activate the proximal signaling molecule Jak2 upon addition of ligand to transfected cells, and, unlike the long PRLr, high concentrations of ligand did not function as a self-antagonist to signaling during intervals of PRL serum elevation, i.e. stress and pregnancy. Given its apparent widespread expression, this PRLr isoform may contribute to PRL action. Furthermore, the functionality of this receptor raises interesting questions regarding the minimal extracellular domain necessary for ligand-induced receptor signaling.

Animals↗
PubMedDate not supplied

A novel and functional interaction between cyclophilin A and prolactin receptor.

Precedent data have revealed that peptidyl isomerases can modulate the function of cell-surface receptors, but no such interactions have been previously shown for the members of the cytokine receptor superfamily. We demonstrate here that a functional interaction occurs between the prolactin receptor (PRLR) and peptidyl prolyl cis/trans isomerase cyclophilin A (CypA). CypA was co-immunoprecipitated with the PRLR in vivo from the breast epithelial cell line T47D and Chinese hamster ovary transfectants overexpressing transfected human PRLR. In addition, in vitro binding assays demonstrated a direct interaction of CypA with the PRLR, in the presence or absence of cyclosporine. Co-immunoprecipitation studies also showed an association of CypA with Jak2. Functional analysis revealed that overexpression of CypA inhibited PRL-induced Rac activation, while simultaneously prolonging Jak2 phosphorylation. These proximal actions had profound downstream effects: CypA overexpression significantly enhanced the basal and PRL-stimulated expression from a beta-casein reporter construct. Hence, the interaction between CypA and the PRLR plays a differential regulatory role in the various signaling pathways leading from the PRLR.

Animals↗