Growth inhibition by bacterial Cas2Em proteins expressed in mammalian cells.

Background: Clustered regularly interspaced short palindromic repeats (CRISPRs) and the CRISPR-associated (Cas) proteins are bacterial adaptive immune system for survival. In our previous study, we demonstrate that polyploid giant bacterial cells (PGBC) induced by Cas2 protein is a step required by new spacer acquisition reaction catalyzed by Cas1/Cas2 complex. We also demonstrated that a carboxyl terminal domain on Cas2Em (the protein Cas2 cloned from Elizabethkingia meningoseptica) is sufficient and enough for PGBC. Thus, the potential role of Cas2Em in microbial-host interaction was explored in this study. Methods: The impacts of Cas2Em on growth of both CHO-K1 and Hela cells were investigated. The subcellular localization and potential molecular target of Ca2Em were studied. Results: The growth of mammalian cells were inhibited by Cas2Em protein via G1 arresting and apoptosis. In addition, we also demonstrated that Cas2Em was tightly associated with nuclear outer membrane and could be immunoprecipitated with 14-3-3 gamma through a 30 amino acid domain (homology of CLK2). Conclusion: Cas2Em significantly suppressed the growth of mammalian cells indicating Cas2 proteins play an important role in mammalian cells.