title: Progesterone signals through membrane progesterone receptors (mPRs) in MDA-MB-468 and mPR-transfected MDA-MB-231 breast cancer cells which lack full-length and N-terminally truncated isoforms of the nuclear progesterone receptor.
abstract: The functional characteristics of membrane progesterone receptors (mPRs) have been investigated using recombinant mPR proteins over-expressed in MDA-MB-231 breast cancer cells. Although these cells do not express the full-length progesterone receptor (PR), it is not known whether they express N-terminally truncated PR isoforms which could possibly account for some progesterone receptor functions attributed to mPRs. In the present study, the presence of N-terminally truncated PR isoforms was investigated in untransfected and mPR-transfected MDA-MB-231 cells, and in MDA-MB-468 breast cancer cells. PCR products were detected in PR-positive T47D Yb breast cancer cells using two sets of C-terminus PR primers, but not in untransfected and mPR-transfected MDA-MB-231 cells, nor in MDA-MB-468 cells. Western blot analysis using a C-terminal PR antibody, 2C11F1, showed the same distribution pattern for PR in these cell lines. Another C-terminal PR antibody, C-19, detected immunoreactive bands in all the cell lines, but also recognized α-actinin, indicating that the antibody is not specific for PR. High affinity progesterone receptor binding was identified on plasma membranes of MDA-MB-468 cells which was significantly decreased after treatment with siRNAs for mPRα and mPRβ. Plasma membranes of MDA-MB-468 cells showed very low binding affinity for the PR agonist, R5020, ≤1% that of progesterone, which is characteristic of mPRs. Progesterone treatment caused G protein activation and decreased production of cAMP in MDA-MB-468 cells, which is also characteristic of mPRs. The results indicate that the progestin receptor functions in these cell lines are mediated through mPRs and do not involve any N-terminally truncated PR isoforms.
authors.affiliation: Marine Science Institute, University of Texas at Austin, 750 Channel View Drive, Port Aransas, TX 78373, USA.
authors.forename: Yefei
authors.initials: Y
authors.lastname: Pang
authors.forename: Peter
authors.initials: P
authors.lastname: Thomas
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D001943:Breast Neoplasms; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D000242:Cyclic AMP / Q000096:biosynthesis; D057075:Enzyme Assays; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000737:chemistry; D006801:Humans; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism*; D011374:Progesterone / Q000494:pharmacology* / Q000502:physiology; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D011980:Receptors, Progesterone / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D010446:Peptide Fragments; D020033:Protein Isoforms; D011980:Receptors, Progesterone; D011994:Recombinant Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D011374:Progesterone; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases