Differential regulation of the transcription factor KLF6 by JNKs and p38 signalling pathways

ANDREOLI, V.; D'ASTOLFO, D; KORITSCHONER, N.P.; CHATTON, B; BOCCO, J.L.

Bariloche-Argentina

Congreso; Combined Meetings: Gene Expression and RNA processing// Cell Biology Signalling and Alternative Splicing; 2007

International Centre for Genetic Engineering and Biotechnology (ICGEB) - Facultad de Ciencias Exactas y

The transcription factor KLF6 is a potential tumor suppressor gene product whose expression level is responsive to external cell stimulation mediated by growth factors, tumor promoters and DNA-damage agents. We demonstrated that this factor interacts with the c-Jun proto-oncoprotein and induces its degradation leading to inhibition of cell proliferation. The JNK family of MAP kinases is the main regulator of c-Jun, contributing to its enhanced transcriptional activity and protein stability. In addition, p38 kinases are also involved in the regulation of c-Jun activity through phosphorylation of AP-1 members, including c-Jun itself. However, the biochemical pathway involved in KLF6 response to extracellular stimuli and the consequences for c-Jun-sustained proliferation or oncogenesis have not been elucidated. We observed that in jnk+/+ cells, the cytoplasmic levels of KLF6 were reduced upon ectopic expression of JNK1 or JNK2. Accordingly, the KLF6 protein levels were markedly reduced in jnk -/- cells upon expression of JNK1 and in a lesser extent by JNK2. Moreover, JNK2 activity was associated to the translocation of KLF6 from the cytoplasm to the nucleus. Additionally, activated p38 isoforms (a, b2, g and d) also decreased KLF6 protein levels in the absence of JNK and ERK activities. Interestingly, KLF6 was phosphorylated in vivo in jnk-/- serum starved cells treated with p38 inhibitor, indicating that constitutive KLF6 phosphorylation is still performed independently of MAPKs activities. In conclusion, these results show that JNK and p38 pathways are mainly involved in the regulation of KLF6 protein stability and KLF6 sub-cellular localization. Thus, increased activity of JNK1 and p38 diminished KLF6 protein levels whereas allowed high stability and activation of c-Jun. Conversely, JNK2 substantially increased KLF6 targeting to the nucleus whereas c-Jun activity was low, suggesting that activated c-Jun and KLF6 are mutually exclusive within the nucleus, correlating with enhanced or reduced cell proliferation rate, respectively.