The HER4 Cytoplasmic Domain, But Not Its C Terminus, Inhibits Mammary Cell Proliferation

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  • Feng, Shu-Mang
  • Sartor, Carolyn I.
  • Hunter, Debra
  • Zhou, Hong
  • Yang, Xihui
  • Caskey, Laura S.
  • Dy, Ruth
  • Muraoka-Cook, Rebecca S.
  • Earp, H. Shelton
Abstract
  • Unlike the proliferative action of other EGF receptor family members, HER4/ErbB4 is often associated with growth inhibitory and differentiation signaling. These actions may involve HER4 two-step proteolytic processing by intra-membraneous γ-secretase, releasing the soluble, intracellular 80kDa HER4 cytoplasmic domain, s80HER4. We demonstrate that pharmacologic inhibition of either γ-secretase activity or HER4 tyrosine kinase activity blocked heregulin-dependent growth inhibition of SUM44 breast cancer cells. We next generated breast cell lines stably expressing GFP-s80HER4 (GFP fused to the N-terminus of the HER4 cytoplasmic domain, residues 676–1308), GFP-CTHER4 (GFP fused to N-terminus of the HER4 C-terminus distal to the tyrosine kinase domain, residues 989–1308) or GFP alone. Both GFP-s80HER4 and GFP-CTHER4 were found in the nucleus, but GFP-s80HER4 accumulated to a greater extent and sustained its nuclear localization. s80HER4 was constitutively tyrosine phosphorylated and treatment of cells with a specific HER family tyrosine kinase inhibitor i) blocked tyrosine phosphorylation; ii) markedly diminished GFP-s80HER4 nuclear localization, and iii) reduced STAT5A tyrosine phosphorylation and nuclear localization as well as GFP-s80HER4:STAT5A interaction. Multiple normal mammary and breast cancer cell lines, stably expressing GFP-s80HER4 (SUM44, MDA-MB-453, MCF10A, SUM102, and HC11) were growth inhibited compared to the same cell line expressing GFP-CTHER4, or GFP alone. The s80HER4-induced cell number reduction was due to slower growth, as rates of apoptosis were equivalent in GFP, GFP-CTHER4, and GFP-s80HER4 expressing cells. Lastly, GFP-s80HER4 enhanced differentiation signaling as indicated by increased basal and prolactin-dependent β–casein expression. These results indicate that surface HER4 tyrosine phosphorylation and ligand-dependent release of s80HER4 are necessary, and s80HER4 signaling is sufficient for HER4-dependent growth inhibition.
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  • Article
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  • In Copyright
Journal title
  • Molecular Endocrinology (Baltimore, Md.)
Journal volume
  • 21
Journal issue
  • 8
Language
  • English
ISSN
  • 1944-9917
  • 0888-8809

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