Cytohesin-2 is essential for the survival of mice and regulates Golgi volume and function

Proteins of the cytohesin family are known for their guanine-nucleotide exchange factor function for ARF-GTPases, mainly for ARF1 and ARF6. While Arf1 and Arf6 deficiency results in embryonic lethality, in vivo functions of cytohesins are rarely described and mostly inconspicuous. We analyzed the role of cytohesin-2 in vivo and in vitro and found that cytohesin-2 full knockout mice die within one day after birth. Mass spectrometry-based organellar proteomics in wildtype and CRISPR-Cas9-generated cytohesin-2-/- C2 myoblasts revealed a markedly altered Golgi compartment. Golgi volumes were reduced in different cytohesin-2-/- cell lines compared to wildtype cells as revealed by immunofluorescence. Reduced Golgi volumes were rescued by introducing cytohesin-2. Finally, we observed that typical functions of the Golgi apparatus were disrupted in cytohesin-2-deficient cells. Cytohesin2-/- C2 myoblasts exhibited significant changes in the galactose / N-acetyl-galactosamine glycosylation on the cell surface compared to wildtype cells when stained with peanut agglutinin. Further, protein secretion was overall reduced in neonatal cytohesin-2-/- mice compared to wildtype as determined by mass spectrometry-based proteomics. This study describes the essential role of cytohesin-2 in neonatal development and a novel function of the protein in Golgi regulation.