ABSTRACT
Changes in protein levels in different components of the apical junctional complex occur in colorectal cancer (CRC). Claudin3 is one of the main constituents of tight junctions, and its overexpression can increase the paracellular flux of macromolecules, as well as the malignant potential of CRC cells. The aim of this study was to investigate the molecular mechanisms involved in the regulation of claudin3 and its prognostic value in CRC. In silico evaluation in each of the CRC consensus molecular subtypes (CMSs) revealed that high expression levels of CLDN3 (gene encoding claudin3) in CMS2 and CMS3 worsened the patients' longterm survival, whereas a decrease in claudin3 levels concomitant with a reduction in phosphorylation levels of epidermal growth factor receptor (EGFR) and insulinlike growth factor 1 receptor (IGF1R) could be achieved by inhibiting Nglycan biosynthesis in CRC cells. We also observed that specific inactivation of these receptor tyrosine kinases (RTKs) led to a decrease in claudin3 levels, and this regulation seems to be mediated by phospholipase C (PLC) and signal transducer and activator of transcription 3 (STAT3) in CRC cells. RTKs are modulated by their Nlinked glycans, and inhibition of Nglycan biosynthesis decreased the claudin3 levels; therefore, we evaluated the correlation between Nglycogenes and CLDN3 expression levels in each of the CRC molecular subtypes. The CMS1 (MSI immune) subtype concomitantly exhibited low expression levels of CLDN3 and Nglycogenes (MGAT5, ST6GAL1, and B3GNT8), whereas CMS2 (canonical) exhibited high gene expression levels of CLDN3 and Nglycogenes (ST6GAL1 and B3GNT8). A robust positive correlation was also observed between CLDN3 and B3GNT8 expression levels in all CMSs. These results support the hypothesis of a mechanism integrating RTK signaling and Nglycosylation for the regulation of claudin3 levels in CRC, and they suggest that CLDN3 expression can be used to predict the prognosis of patients identified as CMS2 or CMS3.
