The CrkL adapter protein is required for type I interferon-dependent gene transcription and activation of the small G-protein Rap1.
We sought to determine the functional role of the CrkL adapter protein and downstream pathways in interferon signaling. In experiments using CrkL(--) mouse embryonic fibroblasts, we found that CrkL is required for IFN alpha-dependent gene transcription via GAS elements, apparently via the formation of DNA-binding complexes with Stat5. On the other hand, gene transcription via ISRE elements is intact in the absence of CrkL, indicating that the regulatory effects on gene transcription are mediated only via the formation of CrkL:Stat5 complexes. Our studies also indicate that activation of the small GTPase Rap1 by IFN alpha is defective in cells lacking CrkL, indicating that the protein plays a critical role in regulating activation of the growth inhibitory C3G/Rap1 pathway. The IFN alpha-inducible activation of the small GTPase Rap1 requires a functional N-terminus SH3 domain in the CrkL protein, while the C-terminus SH3 domain does not appear to play a role in such a CrkL-function. We also demonstrate that both the Tyk-2 and Jak-1 kinases are required for activation of the CrkL/Rap1 pathway, as the Type I IFN-dependent GTP-bound form of Rap1 is inhibited by overexpression of dominant-negative Tyk-2 or Jak-1 mutants and is defective in cells lacking Tyk-2 or Jak-1. Taken altogether, these findings indicate that CrkL provides an important link between Jak-kinases and downstream cascades that play critical roles in IFN-dependent transcriptional regulation and induction of growth inhibitory responses.
Lekmine
Fatima
F
Section of Hematology-Oncology, University of Illinois at Chicago and West Side Veterans Administration medical Center, Chicago, Illinois 60607, USA.
Sassano
Antonella
A
Uddin
Shahab
S
Majchrzak
Beata
B
Miura
Osamu
O
Druker
Brian J
BJ
Fish
Eleanor N
EN
Imamoto
Akira
A
Platanias
Leonidas C
LC
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002478:Cells, Cultured; D004789:Enzyme Activation; D017353:Gene Deletion; D017930:Genes, Reporter; D020735:Guanine Nucleotide-Releasing Factor 2 / Q000378:metabolism; D006801:Humans; D016898:Interferon-alpha / Q000494:pharmacology*; D053613:Janus Kinase 1; D007700:Kinetics; D051379:Mice; D009154:Mutation; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D020218:Response Elements; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism*; D018909:src Homology Domains
D048868:Adaptor Proteins, Signal Transducing; C082869:CRKL protein; D020735:Guanine Nucleotide-Releasing Factor 2; D016898:Interferon-alpha; D009687:Nuclear Proteins; D011505:Protein-Tyrosine Kinases; C507904:JAK1 protein, human; C507905:Jak1 protein, mouse; D053613:Janus Kinase 1; D020827:rap1 GTP-Binding Proteins