#JAK-STAT pathway

Paracrine Factor

Which component of the JAK-STAT pathway acts as a transcription factor?

JAK-STAT cascade involves Janus kinases JAK1-3, Tyk2 constitutively associated with cytokine receptors like interferon alpha, interleukin 6, growth hormone receptors lacking intrinsic kinase. Ligand binding dimerizes receptors activating JAKs autophosphorylating tyrosine residues creating SH2 docking sites for STAT proteins. STAT1-6 family contains SH2, DNA binding, transactivation domains. Upon phosphorylation at Tyr701, STAT dimerizes via reciprocal SH2-phosphotyrosine interactions, translocates to nucleus importin-mediated, binds GAS interferon gamma activated sequence motifs activating interferon response, proliferation, apoptosis genes. JAK is tyrosine kinase not transcription factor, FGF receptor RTK, MAP kinase serine-threonine, thus STAT provides direct transcription factor output.

Ref: Darnell et al., Science 1994: STAT proteins as transcription factors activated by JAK kinases downstream cytokines.

View Details

Cell Signaling ELR Pathways - I

Cross-talk between JAK–STAT and RTK pathways allows activation of

multiple downstream branches, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

View Details

Cell Signaling ELR Pathways - I

Which cytokine induces antiviral state via STAT1/STAT2?

Type-I interferons (IFN-α and IFN-β) are rapidly induced during viral infection and act in both autocrine and paracrine fashion. Binding to the IFNAR receptor activates STAT1/STAT2 and IRF9, which induce hundreds of interferon-stimulated genes that establish an antiviral state, inhibit viral replication and enhance antigen presentation. This response is a cornerstone of innate antiviral immunity.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

View Details

Cell Signaling ELR Pathways - I

JAK–STAT pathway is considered short because it

involves direct transcriptional activation, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

View Details