title: Post-transcriptional regulation of chemokine receptor CXCR4 by estrogen in HER2 overexpressing, estrogen receptor-positive breast cancer cells.
abstract: Expression of the chemokine receptor CXCR4, a G protein-coupled receptor, and HER2, a receptor tyrosine kinase, strongly correlates with the aggressive and metastatic potential of breast cancer cells. We studied estrogen regulation of CXCR4 in estrogen receptor (ER)-positive MCF-7 breast cancer cells overexpressing HER2 (MCF7-HER2). Although estrogen evoked no change in CXCR4 mRNA levels, CXCR4 protein was significantly up-regulated after estrogen treatment of these cells, whereas estrogen had no effect on CXCR4 protein level in parental MCF7 cells that are low in HER2. Use of the CXCR4 specific inhibitor, AMD 3100, indicated that this increase in CXCR4 protein was partially responsible for the increase in estrogen-induced migration of these cells. The estrogen-induced increase in CXCR4 protein in MCF-7-HER2 cells was abrogated by the antiestrogen ICI 182780 and by gefitinib (Iressa; a phospho-tyrosine kinase inhibitor), indicating an ER-mediated effect and confirming involvement of receptor tyrosine kinases, respectively. Using specific pathway inhibitors, we show that the estrogen-induced increase in CXCR4 involves PI3K/AKT, MAPK and mTOR pathways. PI3K/AKT and MAPK pathways are known to result in the phosphorylation and functional inactivation of tuberin (TSC2) of tuberous sclerosis complex thereby negating its inhibitory effects on mTOR, which in turn stimulates the translational machinery. Small interfering RNA (siRNA) mediated knockdown of tuberin elevated the level of CXCR4 protein in MCF7-HER2 cells and also nullified further estrogen up-regulation of CXCR4. This study suggests a pivotal role of PI3 K, MAPK and mTOR pathways, via tuberin, in post-transcriptional control of CXCR4, initiated through estrogen-stimulated crosstalk between ER and HER2. Thus, post-transcriptional regulation of CXCR4 by estrogens acting through ER via kinase pathways may play a critical role in determining the metastatic potential of breast cancer cells.
authors.affiliation: Department of Molecular and Integrative Physiology, University of Illinois, 524 Burrill Hall, 407 South Goodwin Avenue, Urbana, IL 61801-3704, USA.
authors.forename: Surojeet
authors.initials: S
authors.lastname: Sengupta
authors.forename: Rachel
authors.initials: R
authors.lastname: Schiff
authors.forename: Benita S
authors.initials: BS
authors.lastname: Katzenellenbogen
mesh_terms: D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D020847:Estrogen Receptor Modulators / Q000494:pharmacology; D004967:Estrogens / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D020239:Receptor Cross-Talk / Q000187:drug effects / Q000502:physiology; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D019718:Receptors, CXCR4 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D011960:Receptors, Estrogen / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D058570:TOR Serine-Threonine Kinases; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D020847:Estrogen Receptor Modulators; D004967:Estrogens; D048049:Extracellular Signal-Regulated MAP Kinases; D019869:Phosphatidylinositol 3-Kinases; D011494:Protein Kinases; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger; D018719:Erb-b2 Receptor Tyrosine Kinases; D019718:Receptors, CXCR4; D011960:Receptors, Estrogen; D058570:TOR Serine-Threonine Kinases; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; C527276:CXCR4 protein, human; C000624653:TSC2 protein, human; C546842:MTOR protein, human