Which of the following are true about cell signaling?
1) The same ligand could have different effects depending on what other signaling molecules are present at the same time
2) Signaling responses that are very fast are usually the direct result of a change in transcription
3) Endocrine signaling factors require cell-to-cell contact for activation of signaling
4) The same ligand could have different effects if present in different concentrations
5) Some signaling receptors are present inside the nucleus rather than at the cell surface
6) The same ligand could have different effects on different cell types