sZIP, an alternative splice variant of ZIP, antagonizes transcription repression and growth inhibition by ZIP

Recently, we reported a novel transcriptional repressor, ZIP (for zinc finger and G-patch domain-containing), which recruits the Mi-2/NuRD (nucleosome remodeling and deacetylase) complex and represses the expression of epidermal growth factor receptor (EGFR). In doing so, ZIP inhibits cell proliferation and suppresses breast carcinogenesis. Here, we report the cloning and the characterization of an alternatively spliced isoform of ZIP, sZIP. sZIP is an N-terminal truncated form of ZIP, lacking the zinc finger but retaining part of the G-patch domain and C-terminal coiled-coil domain of ZIP. We showed that sZIP could interact with the NuRD complex but lost its DNA-binding capacity. We demonstrated that sZIP antagonizes the transcription repression by ZIP by competing for the binding of the NuRD complex and that sZIP alleviates the growth inhibitory effect of ZIP on hepatocarcinoma cells through attenuating the transcriptional repression of EGFR. Our data provide a finely tuned mechanism for EGFR regulation and add another player for transcription repression.