Comparative O-GlcNAc Proteomic Analysis Reveals a Role of O-GlcNAcylated SAM68 in Lung Cancer Aggressiveness

O-GlcNAcylation is a reversible and dynamic post-translational protein modification catalyzed by O-GlcNAc transferase (OGT). Despite the reported association of O-GlcNAcylation with cancer metastasis, the O-GlcNAc proteome profile for cancer aggressiveness remains largely uncharac-terized. Here we report our comparative O-GlcNAc proteome profiling of 2 differentially invasive lung adenocarcinoma cell lines, which identified 158 down-regulated and 106 up-regulated can-didates in highly invasive cells. Among these differential proteins, a nuclear RNA-binding protein SAM68 (SRC associated in mitosis of 68 kDa) was further investigated. Results showed that SAM68 is O-GlcNAcylated and may interact with OGT in the nucleus. Eleven O-GlcNAcylation sites were identified, and data from mutant analysis suggested that multiple serine residues in the N-terminal region are important for O-GlcNAcylation and the function of SAM68 in modulating cancer cell migration and invasion. Analysis of clinical specimens found that high SAM68 ex-pression was associated with late cancer stages, and patients with high-OGT/high-SAM68 ex-pression in their tumors had poorer overall survival compared to those with low-OGT/low-SAM68 expression. Our study has revealed an invasiveness-associated O-GlcNAc proteome profile and connected O-GlcNAcylated SAM68 to lung cancer aggressiveness.