title: Proteomic signatures of acquired letrozole resistance in breast cancer: suppressed estrogen signaling and increased cell motility and invasiveness.
abstract: Aromatase inhibitors, such as letrozole, have become the first-line treatment for postmenopausal women with estrogen-dependent breast cancer. However, acquired resistance remains a major clinical obstacle. Previous studies demonstrated constitutive activation of the MAPK signaling, overexpression of HER2, and down-regulation of aromatase and ERα in letrozole-resistant breast cancer cells. Given the complex signaling network involved in letrozole-refractory breast cancer and the lack of effective treatment for hormone resistance, further investigation of aromatase inhibitor resistance by a novel systems biology approach may reveal previously unconsidered molecular changes that could be utilized as therapeutic targets. This study was undertaken to characterize for the first time global proteomic alterations occurring in a letrozole-resistant cell line. A quantitative proteomic analysis of the whole cell lysates of LTLT-Ca (resistant) versus AC-1 cells (sensitive) was performed to identify significant protein expression changes. A total of 1743 proteins were identified and quantified, of which 411 were significantly up-regulated and 452 significantly down-regulated (p < 0.05, fold change > 1.20). Bioinformatics analysis revealed that acquired letrozole resistance is associated with a hormone-independent, more aggressive phenotype. LTLT-Ca cells exhibited 84% and 138% increase in migration and invasion compared with the control cells. The ROCK inhibitor partially abrogated the enhanced migration and invasion of the letrozole-resistant cells. Flow cytometric analyses also demonstrated an increase in vimentin and twist expression in letrozole-resistance cells, suggesting an onset of epithelial to mesenchymal transition (EMT). Moreover, targeted gene expression arrays confirmed a 28-fold and sixfold up-regulation of EGFR and HER2, respectively, whereas ERα and pS2 were dramatically reduced by 28-fold and 1100-fold, respectively. Taken together, our study revealed global proteomic signatures of a letrozole-resistant cell line associated with hormone independence, enhanced cell motility, EMT and the potential values of several altered proteins as novel prognostic markers or therapeutic targets for letrozole resistant breast cancer.
authors.affiliation: Department of Basic Pharmaceutical Sciences, College of Pharmacy, Xavier University of Louisiana, New Orleans, LA 70125, USA. stilghma@xula.edu
authors.forename: Syreeta L
authors.initials: SL
authors.lastname: Tilghman
authors.forename: Ian
authors.initials: I
authors.lastname: Townley
authors.forename: Qiu
authors.initials: Q
authors.lastname: Zhong
authors.forename: Patrick P
authors.initials: PP
authors.lastname: Carriere
authors.forename: Jin
authors.initials: J
authors.lastname: Zou
authors.forename: Shawn D
authors.initials: SD
authors.lastname: Llopis
authors.forename: Lynez C
authors.initials: LC
authors.lastname: Preyan
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Williams
authors.forename: Elena
authors.initials: E
authors.lastname: Skripnikova
authors.forename: Melyssa R
authors.initials: MR
authors.lastname: Bratton
authors.forename: Qiang
authors.initials: Q
authors.lastname: Zhang
authors.forename: Guangdi
authors.initials: G
authors.lastname: Wang
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D000577:Amides / Q000494:pharmacology; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000187:drug effects* / Q000235:genetics; D048430:Cell Shape / Q000187:drug effects / Q000235:genetics; D019008:Drug Resistance, Neoplasm / Q000187:drug effects* / Q000235:genetics; D004967:Estrogens / Q000378:metabolism*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D053208:Kaplan-Meier Estimate; D000077289:Letrozole; D008648:Mesoderm / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D009361:Neoplasm Invasiveness; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D040901:Proteomics / Q000379:methods*; D011725:Pyridines / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D014230:Triazoles / Q000494:pharmacology*; D014746:Vimentin / Q000378:metabolism; D054460:rho-Associated Kinases / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: D000577:Amides; D004967:Estrogens; D009363:Neoplasm Proteins; D009570:Nitriles; D047428:Protein Kinase Inhibitors; D011725:Pyridines; D014230:Triazoles; D014746:Vimentin; C108830:Y 27632; D000077289:Letrozole; D054460:rho-Associated Kinases; D020742:rhoA GTP-Binding Protein