Cancer regulator EGFR-ErbB4 heterodimer is stabilized through glycans at the dimeric interface.

EGFR and ErbB4 are the only two members of cancer-regulating ErbB RTKs that maintain the activation of their extracellular ligand-binding domain and intracellular tyrosine kinase domain. EGFR and ErbB4 could form homo and heterodimers upon their activation. Heterodimerization triggers more diverse intracellular pathways compared to homodimerization. Moreover, it is known that N-glycosylation is crucial for the stabilization and activation of EGFR and ErbB4 receptors. Herein, atomistic molecular dynamics were simulated to study the EGFR-ErbB4 heterodimer in the glycosylated and unglycosylated states. It was shown that the EGFR-ErbB4 heterodimer is highly stabilized by glycosylation. The increased stability is most significant at the dimeric interfaces, regulated by packing of three glycans attached to EGFR (Asn337) and ErbB4 (Asn333, Asn523) at the dimeric interface. Finally, it is proposed that heterodimerization is the persistent key player in the EGFR and ErbB4 activation. Thus, targeting the heterodimers in future therapeutic designs could be a promising approach against drug resistance to ErbB-positive cancers.

Glycosylation promotes the cancer regulator EGFR-ErbB2 heterodimer formation - molecular dynamics study.

ErbB family of receptor tyrosine kinases play significant roles in cellular differentiation and proliferation. Mutation or overexpression of these receptors leads to several cancers in humans. The family has four homologous members including EGFR, ErbB2, ErbB3, and ErbB4. From which all except the ErbB2 bind to growth factors via the extracellular domain to send signals to the cell. However, dimerization of the ErbB receptor occurs in extracellular, transmembrane, and intracellular domains. The ErbB receptors are known to form homodimers and heterodimers in the active form. Heterodimerization increases the variety of identified ligands and signaling pathways that can be activated by these receptors. Furthermore, glycosylation of the ErbB receptors has shown to be critical for their stability, ligand binding, and dimerization. Here, atomistic molecular dynamics simulations on the glycosylated and unglycosylated heterodimer showed that the EGFR-ErbB2 heterodimer is more stable in its dynamical pattern compared to the EGFR-EGFR homodimer. This increased stability is regulated by maintaining the dimeric interface by the attached glycans. It was also shown that the presence of various glycosylation sites within the ErbB2 growth factor binding site leads to occlusion of this site by the glycans that inhibit ligand binding to ErbB2 and participate in further stabilization of the heterodimer construct. Putting together, glycosylation seems to promote the heterodimer formation within the ErbB family members as the dominant molecular mechanism of activation for these receptors.

Combined Effects of Protocatechuic Acid and 5-Fluorouracil on p53 Gene Expression and Apoptosis in Gastric Adenocarcinoma Cells.

OBJECTIVES: This study evaluated the combined effects of protocatechuic acid (PCA) and 5-fluorouracil (5-FU) on gastric adenocarcinoma (AGS) cells. MATERIALS AND METHODS: The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, colony formation assay, flow cytometry technique, real-time quantitative polymerase chain reaction, and Western blotting were used to investigate cytotoxic effects, colony formation, apoptosis, p53 gene expression, and Bcl-2 protein level in AGS cells treated with 5-FU and PCA. RESULTS: Our results demonstrated that PCA (500 µM) alone or in combination with 5-FU (10 µM) inhibited AGS cell proliferation, inhibited a colony formation, and increased apoptosis compared with untreated control cells. Moreover, the combined 5-FU/PCA exposure led to upregulation of p53 and downregulation of Bcl-2 protein when compared to the untreated control cells. CONCLUSION: The results demonstrate that the combined 5-FU/PCA may promote antiproliferative and pro-apoptotic effects with the inhibition of colony formation in AGS cells. The mechanisms by which the combined 5-FU/PCA exposure exerts its effects are associated with upregulation of p53 gene expression and downregulation of Bcl-2 level. Therefore, the combination of 5-FU with PCA not only could be a promising approach to potentially reduce the dose requirements of 5-FU but also could promote apoptosis via p53 and Bcl-2 signaling pathways.