Prolactin (PRL)-stimulated ubiquitination of ZnT2 mediates a transient increase in zinc secretion followed by ZnT2 degradation in mammary epithelial cells

J Biol Chem. 2014 Aug 22;289(34):23653-61. doi: 10.1074/jbc.M113.531145. Epub 2014 Jul 11.


The zinc transporter ZnT2 imports zinc into secretory vesicles and regulates zinc export from the mammary epithelial cell. Mutations in ZnT2 substantially impair zinc secretion into milk. The lactogenic hormone prolactin (PRL) transcriptionally increases ZnT2 expression through the Jak2/STAT5 signaling pathway, increasing zinc accumulation in secretory vesicles and zinc secretion. Herein, we report that PRL post-translationally stimulated ZnT2 ubiquitination, which altered ZnT2 trafficking and augmented vesicular zinc accumulation and secretion from mammary epithelial cells in a transient manner. Ubiquitination then down-regulated zinc secretion by stimulating degradation of ZnT2. Mutagenesis of two N-terminal lysine residues (K4R and K6R) inhibited ZnT2 ubiquitination, vesicular zinc accumulation and secretion, and protein degradation. These findings establish that PRL post-translationally regulates ZnT2-mediated zinc secretion in a multifactorial manner, first by enhancing zinc accumulation in vesicles to transiently enhance zinc secretion and then by activating ubiquitin-dependent ZnT2 degradation. This provides insight into novel mechanisms through which ZnT2 and zinc transport is tightly regulated in mammary epithelial cells.

Keywords: Mammary Gland; Prolactin; Protein Degradation; Secretion; Ubiquitination; Zinc Transporter; ZnT2.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Base Sequence
  • Cation Transport Proteins / genetics
  • Cation Transport Proteins / metabolism
  • Cation Transport Proteins / physiology*
  • Cell Line
  • Epithelial Cells / metabolism
  • Female
  • Immunoprecipitation
  • Lysine / metabolism
  • Mammary Glands, Animal / cytology
  • Mammary Glands, Animal / metabolism*
  • Mice
  • Prolactin / physiology*
  • Protein Processing, Post-Translational
  • RNA, Small Interfering
  • Ubiquitination / physiology*


  • Cation Transport Proteins
  • RNA, Small Interfering
  • Znt2 protein, mouse
  • Prolactin
  • Lysine