title: Protein kinase Calpha determines HER2 fate in breast carcinoma cells with HER2 protein overexpression without gene amplification.
abstract: In some HER2-positive breast tumors, cell surface overexpression of HER2 is not associated with gene amplification but may instead rest in altered gene transcription, half-life, or recycling of the oncoprotein. Here, we show that HER2 overexpression in HER2 2+ carcinomas is associated with neither an increase in gene transcription nor a deregulation in the ubiquitin-dependent pathways, but instead seems to be regulated by protein kinase Calpha (PKCalpha) activity. The stimulation of PKCalpha up-regulated HER2 expression, whereas PKCalpha inhibition by pharmacologic treatments and PKCalpha-specific small interfering RNA led to a dramatic down-regulation of HER2 levels only in breast cancer cells HER2 2+. Consistent with the in vitro data, our biochemical analysis of HER2 2+ human primary breast specimens revealed significantly higher levels of phosphorylated PKCalpha compared with HER2-negative tumors. Inhibition of HER2 activation by the tyrosine kinase inhibitor lapatinib led to decreased levels of PKCalpha phosphorylation, clearly indicating a cross-talk between PKCalpha and HER2 molecules. These data suggest that HER2 overexpression in HER2 2+ carcinomas is due to an accumulation of the recycled oncoprotein to the cell surface induced by activated PKCalpha.
authors.affiliation: Molecular Targeting Unit, Department of Experimental Oncology, National Cancer Institute, Foundation IRCCS, Milan, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Magnifico
authors.forename: Luisa
authors.initials: L
authors.lastname: Albano
authors.forename: Stefano
authors.initials: S
authors.lastname: Campaner
authors.forename: Manuela
authors.initials: M
authors.lastname: Campiglio
authors.forename: Silvana
authors.initials: S
authors.lastname: Pilotti
authors.forename: Sylvie
authors.initials: S
authors.lastname: Ménard
authors.forename: Elda
authors.initials: E
authors.lastname: Tagliabue
mesh_terms: D001943:Breast Neoplasms / Q000201:enzymology* / Q000235:genetics; D002227:Carbazoles / Q000494:pharmacology; D045744:Cell Line, Tumor; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005784:Gene Amplification; D006801:Humans; D047468:Immunoprecipitation; D007211:Indoles / Q000494:pharmacology; D051571:Protein Kinase C-alpha / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D050721:Proto-Oncogene Proteins c-cbl / Q000096:biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000096:biosynthesis* / Q000235:genetics; D014162:Transfection
chemical_list: D002227:Carbazoles; D004791:Enzyme Inhibitors; D004815:Epidermal Growth Factor; D007211:Indoles; D051571:Protein Kinase C-alpha; D050721:Proto-Oncogene Proteins c-cbl; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D018719:Erb-b2 Receptor Tyrosine Kinases; C081021:Go 6976; C067419:CBL protein, human