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Characterization and functional analysis of a heart-enriched DnaJ/ Hsp40 homolog dj4/DjA4

Khaleque Md Abdul1, Kazutoyo Terada, Tomomi Gotoh

  • 1Department of Molecular Genetics, Kumamoto University School of Medicine, Japan.

Cell Stress & Chaperones
|October 17, 2002
PubMed

Insights

The novel chaperone DjA4, a DnaJ homolog, is highly expressed in heart and testis. DjA4, along with Hsp70, protects heart muscle cells from stress, enhancing cell survival.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • DnaJ homologs are cochaperones of heat shock protein 70 (Hsp70) family.
  • Dj1, Dj2, and Dj3 are known mammalian cytosolic DnaJ homologs.
  • Dj4 (DjA4) is a newly identified DnaJ homolog.

Purpose of the Study:

  • Characterize the novel DjA4 chaperone.
  • Compare DjA4 with other chaperones.
  • Investigate the role of DjA4 in cellular stress response, particularly in heart muscle cells.

Main Methods:

  • mRNA and protein expression analysis in various mouse tissues.
  • Subcellular fractionation of mouse heart.
  • Immunocytochemical analysis of H9c2 heart muscle cells.
  • Cell differentiation and heat shock treatments.
  • Overexpression studies of chaperones in H9c2 cells.

Main Results:

  • DjA4 mRNA and protein are highly expressed in heart and testis.
  • DjA4 is primarily located in the cytosol of heart muscle cells.
  • DjA4 and Hsc70 colocalize in the cytoplasm under normal conditions and in the nucleus after heat shock.
  • DjA4 expression increases significantly during H9c2 cell differentiation.
  • DjA4, Hsp70, Dj1, and Dj2 are induced by heat shock, while Hsc70 and Dj3 are not.
  • Co-overexpression of DjA4 or Dj2 with Hsp70 enhances H9c2 cell survival after severe heat shock.

Conclusions:

  • DjA4 is a significant chaperone, particularly in heart and testis.
  • The Hsc70/Hsp70-DjA4 chaperone pair plays a protective role in heart muscle cells against various stresses.
  • DjA4 contributes to cellular thermotolerance and survival under stress conditions.

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