Why does c-Jun migrate at a higher molecular weight after treatment?

The transcriptional activity of c-Jun is regulated by SAPK/JNK phosphorylation at Ser63 and Ser73. The signaling pathway can be found at https://www.cellsignal.com/contents/science-pathway-research-mapk-signaling/sapk-jnk-signaling-pathway/pathways-mapk-sapk. Cellular stressors, such as UV radiation, inflammatory cytokines, or ceramide, activate Rho-family GTPases and subsequent MAPKKK (Map Kinase Kinase Kinase) pathways. MAPKKKs can activate MKK4/7, which directly phosphorylate and activate SAPK/JNK. Upon translocation to the nucleus, SAPK/JNK can activate c-Jun and other transcription factors. Proteins generally undergo a phosphorylation dependent mobility shift (PDMS) in SDS-PAGE. This shift can vary from target to target, and even with different activation events on the same target. Recent experiments suggest this is due to the additional negative charge conferred by phosphorylation sites disrupting protein binding to SDS (see https://www.researchgate.net/publication/264031559_Phosphorylation-Dependent_Mobility_Shift_of_Proteins_on_SDS-PAGE_is_Due_to_Decreased_Binding_of_SDS). As UV-treatment is a known activator of SAPK/JNK pathway, it is a useful model for c-Jun activation, which is accompanied by a corresponding PDMS. Many cell lines and tissue samples will have some detectable basal level of phosphorylated SAPK/JNK. As long as this is present, there may also be some basal level of activated c-Jun as well.

Last updated: February 27, 2024