Huntingtin-interacting proteins, HIP14 and HIP14L, mediate dual functions, palmitoyl acyltransferase and Mg2+ transport

J Biol Chem. 2008 Nov 28;283(48):33365-74. doi: 10.1074/jbc.M801469200. Epub 2008 Sep 15.


Polyglutamine expansions of huntingtin protein are responsible for the Huntington neurological disorder. HIP14 protein has been shown to interact with huntingtin. HIP14 and a HIP14-like protein, HIP14L, with a 69% similarity reside in the Golgi and possess palmitoyl acyltransferase activity through innate cysteine-rich domains, DHHC. Here, we used microarray analysis to show that reduced extracellular magnesium concentration increases HIP14L mRNA suggesting a role in cellular magnesium metabolism. Because HIP14 was not on the microarray platform, we used real-time reverse transcriptase-PCR to show that HIP14 and HIP14L transcripts were up-regulated 3-fold with low magnesium. Western analysis with a specific HIP14 antibody also showed that endogenous HIP14 protein increased with diminished magnesium. Furthermore, we demonstrate that when expressed in Xenopus oocytes, HIP14 and HIP14L mediate Mg2+ uptake that is electrogenic, voltage-dependent, and saturable with Michaelis constants of 0.87 +/- 0.02 and 0.74 +/- 0.07 mm, respectively. Diminished magnesium leads to an apparent increase in HIP14-green fluorescent protein and HIP14L-green fluorescent fusion proteins in the Golgi complex and subplasma membrane post-Golgi vesicles of transfected epithelial cells. We also show that inhibition of palmitoylation with 2-bromopalmitate, or deletion of the DHHC motif HIP14DeltaDHHC, diminishes HIP14-mediated Mg2+ transport by about 50%. Coexpression of an independent protein acyltransferase, GODZ, with the deleted HIP14DeltaDHHC mutant restored Mg2+ transport to values observed with wild-type HIP14. Although we did not directly measure palmitoylation of HIP14 in these studies, the data are consistent with a regulatory role of autopalmitoylation in HIP14-mediated Mg2+ transport. We conclude that the huntingtin interacting protein genes, HIP14 and HIP14L, encode Mg2+ transport proteins that are regulated by their innate palmitoyl acyltransferases thus fulfilling the characteristics of "chanzymes."

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acyltransferases / genetics
  • Acyltransferases / metabolism*
  • Adaptor Proteins, Signal Transducing / genetics
  • Adaptor Proteins, Signal Transducing / metabolism*
  • Animals
  • COS Cells
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Chlorocebus aethiops
  • Dogs
  • Gene Expression Profiling
  • Gene Expression Regulation, Enzymologic
  • Golgi Apparatus / enzymology*
  • Humans
  • Ion Transport / physiology
  • Magnesium / metabolism*
  • Mice
  • Mutation
  • Nerve Tissue Proteins / genetics
  • Nerve Tissue Proteins / metabolism*
  • Oligonucleotide Array Sequence Analysis
  • Protein Structure, Tertiary / physiology
  • Xenopus


  • Adaptor Proteins, Signal Transducing
  • Carrier Proteins
  • Nerve Tissue Proteins
  • Acyltransferases
  • ZDHHC17 protein, human
  • Magnesium