Heterogeneous nuclear ribonucleoprotein K interacts with and is proteolyzed by calpain in vivo.
Calpain is a cytosolic "modulator protease" that modulates cellular functions in response to Ca2+. To identify in vivo substrates of calpain, yeast two-hybrid screening was done using the 5-EF-hand (penta-EF-hand; PEF) domain of the micro-calpain large subunit (domain IV), since several possible in vivo substrates for calpain have been previously reported to bind to the 5-EF-hand domains. Other than the regulatory subunit of calpain, which binds to the domain IV, heterogeneous nuclear ribonucleoproteins (hnRNP) K and R were identified, and shown to be proteolyzed by micro-calpain in vitro. When expressed in COS7 cells, hnRNP K and micro-calpain co-localized in the cytosol, and Ca2+-ionophore stimulation of the cells resulted in proteolysis of hnRNP K, indicating that hnRNP K is an in vivo substrate for calpain. Now, hnRNP K is considered to function as a scaffold protein for its binding proteins, such as PKCdelta and C/EBPbeta, which were reported to be calpain substrates, suggesting that hnRNP-K is a scaffold for calpain to proteolyze these proteins.
Kimura
Eiichi
E
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
Abe
Keiko
K
Suzuki
Koichi
K
Sorimachi
Hiroyuki
H
D000818:Animals; D019556:COS Cells; D000001:Calcimycin / Q000494:pharmacology; D002154:Calpain / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D020832:EF Hand Motifs; D004926:Escherichia coli / Q000378:metabolism; D034641:Heterogeneous-Nuclear Ribonucleoprotein K; D006801:Humans; D007476:Ionophores / Q000494:pharmacology; D021122:Protein Subunits; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012261:Ribonucleoproteins / Q000378:metabolism*; D014162:Transfection; D020798:Two-Hybrid System Techniques; D015003:Yeasts / Q000235:genetics
D034641:Heterogeneous-Nuclear Ribonucleoprotein K; D007476:Ionophores; D021122:Protein Subunits; D011994:Recombinant Proteins; D012261:Ribonucleoproteins; C072074:HNRNPK protein, human; D000001:Calcimycin; D002154:Calpain