Functional interaction of Sam68 and heterogeneous nuclear ribonucleoprotein K.
Sam68 is a target of the c-Src tyrosine kinase. We previously showed that overexpression of Sam68 functionally substitutes for, as well as synergies with, HIV-1 Rev in Rev-response element (RRE)-mediated gene expression and virus replication. Here we describe the identification of heterogeneous nuclear ribonucleoprotein K (hnRNP K) as a protein that specifically interacts with Sam68 in vitro and in vivo. HnRNP K did not bind to RRE-RNA directly, but formed a super complex with Sam68 and RRE in vitro. RNase treatment did not change the strength of binding of hnRNP K to Sam68. We demonstrated that hnRNP K significantly inhibited Sam68-mediated, but not Rev-mediated, RRE-dependent gene expression. We further showed that Sam68, but not a non-functional mutant Sam68p21, inhibited transcriptional activation of CT element by hnRNP K. Interestingly, the Sam68p21 with a single amino acid substitution in the nuclear localization domain exhibited less affinity for hnRNP K in vitro. We propose that the direct interaction of Sam68 and hnRNP K adversely affect the activities of both proteins in signal transduction pathways of both transcriptional and post-transcriptional events.
Yang
Jian-Ping
JP
Department of Biology, University of California, San Diego, La Jolla, California, CA 92093-0665, USA.
Reddy
Thipparthi R
TR
Truong
Ky T
KT
Suhasini
Modem
M
Wong-Staal
Flossie
F
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D019556:COS Cells; D002478:Cells, Cultured; D004268:DNA-Binding Proteins; D003609:Dactinomycin / Q000494:pharmacology; D005786:Gene Expression Regulation; D015752:Genes, env; D006367:HeLa Cells; D034641:Heterogeneous-Nuclear Ribonucleoprotein K / Q000378:metabolism*; D006801:Humans; D011485:Protein Binding; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D016601:RNA-Binding Proteins / Q000378:metabolism*; D015398:Signal Transduction; D020798:Two-Hybrid System Techniques
D048868:Adaptor Proteins, Signal Transducing; D004268:DNA-Binding Proteins; D034641:Heterogeneous-Nuclear Ribonucleoprotein K; C489559:KHDRBS1 protein, human; D016601:RNA-Binding Proteins; D003609:Dactinomycin