Question

What happens to STAT dimers in response to cytokine receptor activation?

a) They bind to JAKs in the cytoplasm.
b) They stimulate Ras signaling.
c) They associate with membrane-bound GTP binding proteins.
d) They translocate into the nucleus.

Answer 1

STAT dimers, upon phosphorylation by activated JAKs, translocate into the nucleus where they act as transcription factors. This is part of the downstream cellular response to cytokine receptor activation, which leads to changes in gene expression.

Step-by-step explanation:

The question concerns the response of STAT dimers to cytokine receptor activation in cell signaling pathways. When a cytokine receptor is activated, typically through the binding of a signaling molecule, the receptor undergoes dimerization and autophosphorylation. This is part of a cellular response mechanism that leads to activation of associated Janus kinases (JAKs). The activated JAKs then phosphorylate STAT proteins, which dimerize in the cytoplasm.

Following dimerization, the correct response is (d) They translocate into the nucleus. In the nucleus, these STAT dimers act as transcription factors to influence gene expression, thereby initiating the downstream cellular response, such as protein expression, cellular metabolism, or cell division depending on the specific cytokine signal.

The phosphorylation cascade is crucial for transmitting the signal from the receptor to the DNA in the nucleus. The interaction between signaling molecules and cytokine receptors does not directly involve GTP exchange as seen with G-protein coupled receptors nor does it stimulate Ras signaling directly from binding.