Identification of Mrj, a DnaJ/Hsp40 family protein, as a keratin 8/18 filament regulatory protein.
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.
Izawa
I
I
Division of Biochemistry, Aichi Cancer Center Research Institute, Chikusa-ku, Nagoya, Aichi 464-8681, Japan.
Nishizawa
M
M
Ohtakara
K
K
Ohtsuka
K
K
Inada
H
H
Inagaki
M
M
D000906:Antibodies / Q000276:immunology; D018076:DNA, Complementary; D050956:HSP40 Heat-Shock Proteins; D006367:HeLa Cells; D006801:Humans; D007382:Intermediate Filaments / Q000378:metabolism*; D007633:Keratins / Q000235:genetics / Q000378:metabolism*; D008845:Microinjections; D018832:Molecular Chaperones / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D009419:Nerve Tissue Proteins; D017384:Sequence Deletion
D000906:Antibodies; D018076:DNA, Complementary; C485565:DNAJB6 protein, human; D050956:HSP40 Heat-Shock Proteins; D018832:Molecular Chaperones; D009419:Nerve Tissue Proteins; D007633:Keratins