title: Pnck overexpression in HER-2 gene-amplified breast cancer causes Trastuzumab resistance through a paradoxical PTEN-mediated process.
abstract: The gene for Pregnancy Up-regulated Non-ubiquitous Calmodulin Kinase (Pnck), a novel calmodulin kinase, is expressed in roughly one-third of human breast tumors, but not in adjoining normal tissues. Pnck alters EGFR stability and function, prompting this study to determine if Pnck expression has implications for HER-2 function and HER-2-directed therapy. The frequency of Pnck expression in HER-2-amplified breast cancer was examined by immunohistochemistry, and the impact of Pnck expression in the presence of HER-2 amplification on cancer cell proliferation, clonogenicity, cell-cycle progression, and Trastuzumab sensitivity was examined in vitro by transfection of cells with Pnck. Cell signaling was probed by Western blot analysis and shRNA-mediated PTEN knockdown. Over 30 % of HER-2 amplified tumors were found to express Pnck. Expression of Pnck in SkBr3 cells resulted in increased proliferation, clonal growth, cell-cycle progression, and Trastuzumab resistance. Pnck expression increases Hsp27 expression, Trastuzumab partial agonist activity on HER-2 Y1248 phosphorylation, and suppressed extracellular signal-regulated kinase (ERK1/2) activity. Knockdown of endogenous PTEN upregulated ERK1/2 activity, inhibited cellular proliferation, and partially sensitized Pnck/SKBr3 cells to Trastuzumab treatment. Increased proliferation of the Pnck/SKBr3 cells was observed following expression of protein phosphatase active and lipid phosphatase dead PTEN mutant but not the total phosphatase dead PTEN mutant. Co-overexpression of HER-2 and Pnck results in enhanced tumor cell proliferation and Trastuzumab resistance that is paradoxically dependent on PTEN protein phosphatase activity. This suggests that Pnck may be a marker of Trastuzumab resistance and possibly a therapeutic target.
authors.affiliation: Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, New Research Building, W412/W417, 3970 Reservoir Road NW, Washington, DC, 20057, USA, tbd@georgetown.edu.
authors.forename: Tushar B
authors.initials: TB
authors.lastname: Deb
authors.forename: Annie H
authors.initials: AH
authors.lastname: Zuo
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Barndt
authors.forename: Surojeet
authors.initials: S
authors.lastname: Sengupta
authors.forename: Radmila
authors.initials: R
authors.lastname: Jankovic
authors.forename: Michael D
authors.initials: MD
authors.lastname: Johnson
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D014408:Biomarkers, Tumor / Q000235:genetics / Q000378:metabolism; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D054729:Calcium-Calmodulin-Dependent Protein Kinase Type 1 / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002470:Cell Survival; D019008:Drug Resistance, Neoplasm; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D005784:Gene Amplification; D015870:Gene Expression; D006801:Humans; D020890:Neuregulin-1 / Q000502:physiology; D051059:PTEN Phosphohydrolase / Q000502:physiology*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics*; D059807:S Phase Cell Cycle Checkpoints; D000068878:Trastuzumab / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D014408:Biomarkers, Tumor; D054729:Calcium-Calmodulin-Dependent Protein Kinase Type 1; D048049:Extracellular Signal-Regulated MAP Kinases; D020890:Neuregulin-1; D051059:PTEN Phosphohydrolase; D018719:Erb-b2 Receptor Tyrosine Kinases; D000068878:Trastuzumab; C092262:heregulin beta 1 (177-244); C508053:ERBB2 protein, human; C517606:PNCK protein, human; C494929:PTEN protein, human