To Investigate the Role of N-Linked Glycosylated Carcinoembryonic Antigen-Related Cell Adhesion Molecule 6 (Ceacam6) in Egf Receptor Signaling and the Implication in Oral Cancer Therapy

Aberrant protein glycosylation could be a distinct feature of cancer cells that influences cancer progression and metastasis because it regulates membrane protein folding which alters receptor activation and changes epitope exposure for antibody (Ab) recognition. Carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6), a glycophosphoinositol (GPI)-anchor protein, is a heavily-glycosylated molecule. However, the pathological significance of CEACAM6 glycosylation has not been addressed in oral squamous cell carcinoma. We recently developed an anti-CEACAM6 heavy-chain (HC)Ab (namely TMU HCAb) from an immune llama library. The TMU HCAb had a better ability to recognize glycosylated CEACAM6 compared to the conventional antibodies. Using the TMU HCAb, we found that glycosylated CEACAM6 was a tumor marker associated with recurrence in early-stage oral OSCC patients. CEACAM6 promoted OSCC cell invasion, migration, cytoskeletal rearrangement, and metastasis via interaction with enhancing epidermal growth factor EGF receptor (EGFR) and enhancing EGFR activation, clustering, and intracellular signaling cascades. These functions were modulated by N-acetylglucosaminyltransferase 5 (MGAT5) which mediated N-glycosylation at Asn256 (N256) of CEACAM6 (European Journal of Cancer 2016; 61, Suppl. 1, S9–S218). The results indicated that N-glycosylation of CEACAM6 regulates EGFR signaling of OSCC metastasis and could be a theranostic marker for OSCC. Therefore, this proposal aims to understand the molecular mechanisms including: (1) Does N-glycosylation of CEACAM6 regulates EGFR signaling through receptor dimerization and intracellular trafficking? (2) How does N-glycosylation regulates the CEACAM6/EGFR interactions? In addition, we will also investigate (3) whether glycosylated CEACAM6 could be a surrogate marker for anti-EGFR therapy and examine whether a combination of anti-CEACAM6 (such as the antibody and shRNA) and anti-EGFR treatment achieve better therapeutic effects against OSCC. Three specific aims are listed below to achieve our goals. Aim 1. To investigate the effect of glycosylated CEACAM6 in EGFR dimerization and EGFR trafficking. Aim 2. To investigate the involvement of N-glycosylation in the CEACAM6/EGFR interaction and to investigate whether the N-glycosylation affects the localization of CEACAM6/EGFR complex in lipid-raft. Aim 3. To investigate the correlation between glycosylated CEACAM6 and EGFR activation in clinical OSCC tissues and to examine whether targeting CEACAM6 enhances the therapeutic effect of anti-EGFR therapy on OSCC growth and metastasis. Because there is no significant OSCC marker for target therapy, the current treatments of OSCC are still limited in surgery, radiotherapy and chemotherapy. In addition, the anti-EGFR treatments do not improve the outcome of OSCC patients. Therefore, the glycosylated CEACAM6 could be a novel target for OSCC therapy and could be a surrogate marker for anti-EGFR treatments.