Identification of Mrj, a DnaJ/Hsp40 family protein, as a keratin 8/18 filament regulatory protein

J Biol Chem. 2000 Nov 3;275(44):34521-7. doi: 10.1074/jbc.M003492200.


To elucidate the function of keratins 8 and 18 (K8/18), major components of the intermediate filaments of simple epithelia, we searched for K8/18-binding proteins by screening a yeast two-hybrid library. We report here that human Mrj, a DnaJ/Hsp40 family protein, directly binds to K18. Among the interactions between DnaJ/Hsp40 family proteins and various intermediate filament proteins that we tested using two-hybrid methods, Mrj specifically interacted with K18. Immunostaining with anti-Mrj antibody showed that Mrj colocalized with K8/18 filaments in HeLa cells. Mrj was immunoprecipitated not only with K18, but also with the stress-induced and constitutively expressed heat shock protein Hsp/c70. Mrj bound to K18 through its C terminus and interacted with Hsp/c70 via its N terminus, which contains the J domain. Microinjection of anti-Mrj antibody resulted in the disorganization of K8/18 filaments, without effects on the organization of actin filaments and microtubules. Taken together, these results suggest that Mrj may play an important role in the regulation of K8/18 filament organization as a K18-specific co-chaperone working together with Hsp/c70.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies / immunology
  • DNA, Complementary
  • HSP40 Heat-Shock Proteins
  • HeLa Cells
  • Humans
  • Intermediate Filaments / metabolism*
  • Keratins / genetics
  • Keratins / metabolism*
  • Microinjections
  • Molecular Chaperones / genetics
  • Molecular Chaperones / immunology
  • Molecular Chaperones / metabolism*
  • Nerve Tissue Proteins*
  • Sequence Deletion


  • Antibodies
  • DNA, Complementary
  • DNAJB6 protein, human
  • HSP40 Heat-Shock Proteins
  • Molecular Chaperones
  • Nerve Tissue Proteins
  • Keratins