Journal
CANCER RESEARCH
Volume 67, Issue 11, Pages 5308-5317Publisher
AMER ASSOC CANCER RESEARCH
DOI: 10.1158/0008-5472.CAN-06-3936
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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 Cot PKC alpha) activity. The stimulation of PKC alpha up-regulated HER2 expression, whereas PKC(alpha inhibition by pharmacologic treatments and PKC(x-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 PKC(alpha compared with HER2-negative tumors. Inhibition of HER2 activation by the tyrosine kinase inhibitor lapatinib led to decreased levels of PKC alpha phosphorylation, clearly indicating a cross-talk between PKC alpha, 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 PKC alpha.
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