Cyclic AMP (cAMP)-dependent proteolysis of GATA6 by proteasome: Zinc-finger domain of GATA6 has signals for nuclear export and proteolysis, both of which are responsive to cAMP.

Abstract

Transcription factor GATA6 stably expressed in Chinese hamster ovary (CHO)-K1 cells is exported from the nucleus to the cytoplasm and degraded there by proteasome upon treatment with dibutylyl-cyclic AMP (dbcAMP), which is a membrane-permeable cyclic AMP (cAMP) analogue. The cAMP-dependent proteolysis of GATA6 was characterized by dissection of the GATA6 protein into a zinc-finger domain (Zf) and the surrounding region (ΔZf). These segments were separately expressed in CHO-K1 cells stably, and followed by treatment with dbcAMP. The nuclear localized Zf was degraded by proteasome similarly to the full-length GATA6. Site-directed mutants of nuclear localizing signal (NLS) (345RKRKPK350 → AAAAPK and AAAAPA) and closely related GATA4 showed the same behavior. Although nuclear-localized ΔZf was degraded by proteasome, the cytoplasmic-located ΔZf was resistant to proteolysis in contrast to the NLS mutants. We also searched for a potential NLS and nuclear export signal (NES) with computational prediction programs and compared the results with ours. All these results suggest that the amino acid sequence(s) of the Zf of GATA6 is responsive to cAMP-dependent nuclear export and proteolysis.