Platelet-derived growth factor induces phosphorylation of multiple JAK family kinases and STAT proteins.
Receptors for interferons and other cytokines signal through the action of associated protein tyrosine kinases of the JAK family and latent cytoplasmic transcription factors of the STAT family. Genetic and biochemical analysis of interferon signaling indicates that activation of STATs by interferons requires two distinct JAK family kinases. Loss of either of the required JAKs prevents activation of the other JAK and extinguishes STAT activation. These observations suggest that JAKs provide interferon receptors with a critical catalytic signaling function and that at least two JAKs must be incorporated into an active receptor complex. JAK and STAT proteins are also activated by ligands such as platelet-derived growth factor (PDGF), which act through receptors that possess intrinsic protein tyrosine kinase activity, raising questions about the role of JAKs in signal transduction by this class of receptors. Here, we show that all three of the ubiquitously expressed JAKs--JAK1, JAK2, and Tyk2--become phosphorylated on tyrosine in both mouse BALB/c 3T3 cells and human fibroblasts engineered to express the PDGF-beta receptor. All three proteins are also associated with the activated receptor. Through the use of cell lines each lacking an individual JAK, we find that in contrast to interferon signaling, PDGF-induced JAK phosphorylation and activation of STAT1 and STAT3 is independent of the presence of any other single JAK but does require receptor tyrosine kinase activity. These results suggests that the mechanism of JAK activation and JAK function in signaling differs between receptor tyrosine kinases and interferon receptors.
Vignais
M L
ML
Cold Spring Harbor Laboratory, New York 11724, USA.
Sadowski
H B
HB
Watling
D
D
Rogers
N C
NC
Gilman
M
M
D016475:3T3 Cells; D000818:Animals; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D053613:Janus Kinase 1; D053614:Janus Kinase 2; D051379:Mice; D008807:Mice, Inbred BALB C; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D017479:Receptors, Platelet-Derived Growth Factor / Q000187:drug effects / Q000378:metabolism*; D050794:STAT1 Transcription Factor; D050796:STAT3 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism
D004268:DNA-Binding Proteins; D010982:Platelet-Derived Growth Factor; D011518:Proto-Oncogene Proteins; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; C494080:Stat1 protein, mouse; C494087:Stat3 protein, mouse; D015534:Trans-Activators; D014443:Tyrosine; D011505:Protein-Tyrosine Kinases; D017479:Receptors, Platelet-Derived Growth Factor; C507904:JAK1 protein, human; C507924:JAK2 protein, human; C507905:Jak1 protein, mouse; C507926:Jak2 protein, mouse; D053613:Janus Kinase 1; D053614:Janus Kinase 2