Transcriptional activation of carbonic anhydrase III (CAIII) mediated by SP1

Abstract

Background Carbonic anhydrase III (CAIII) is among the least characterized carbonic anhydrase isoforms, particularly in cancer. Although CAIII has been suggested to contribute to cellular antioxidant defense due to its high cysteine content, limited data exist regarding its expression patterns and transcriptional regulation in malignancies. Previous studies have shown that CAIII can be regulated by hypoxia and signaling pathways such as PI3K and MAPK/ERK; however, its regulation under normoxic conditions remains largely unknown. Methods and Results Here, we investigated the transcriptional regulation of the human CAIII gene. In silico analysis demonstrated high sequence conservation within the proximal promoter region of CAIII among human, mouse, and rat, and no CpG island was detected. Promoter deletion assays identified the −236 to +86 region as the core active promoter, which contains multiple SP1 binding sites. Overexpression of SP1 significantly increased CAIII mRNA and protein levels. Transient transfection assays further confirmed that SP1 enhances the activity of CAIII promoter constructs. Electrophoretic mobility shift assays demonstrated direct binding of SP1 to the CAIII promoter, while mutation of SP1 binding elements abolished DNA–protein complex formation, confirming the specificity of this interaction. Conclusions This study provides the first detailed characterization of the human CAIII promoter and identifies SP1 as a critical transcriptional regulator of CAIII through direct promoter binding. These findings provide new insights into the molecular regulation of CAIII and establish a foundation for future studies exploring its biological and pathological roles.