Peptide G-Protein-Coupled Receptors and ErbB Receptor Tyrosine Kinases in Cancer

Simple Summary Cancer growth is regulated by receptor tyrosine kinases (RTKs) and G-protein-coupled receptors (GPCRs). The epidermal growth factor receptor (EGFR) is an RTK that binds ligands and causes tyrosine phosphorylation of protein substrates. Alternatively, the EGFR can tyrosine itself, leading to the activation of the ERK pathway, increasing cellular proliferation. The EGFR is mutated in several lung cancer patients, and these patients can be treated with tyrosine kinase inhibitors. The neurotensin receptor (NTSR1) is a GPCR, which binds peptides and alters signal transduction. Adding neurotensin to lung cancer cells increases phosphatidylinositol turnover, resulting in elevating cytosolic Ca2+ and activating protein kinase C. SR48692 is an NTSR1 antagonist, which inhibits lung cancer proliferation. RTKs and GPCRs can act independently to alter cancer growth; however, NTSR1 regulates the tyrosine phosphorylation of RTKs such as the EGFR. RTKs and GPCRs interact to increase cancer proliferation. The ErbB RTKs (EGFR, HER2, HER3, and HER4) have been well-studied in cancer. EGFR, HER2, and HER3 stimulate cancer proliferation, principally by activating the phosphatidylinositol-3-kinase and extracellular signal-regulated kinase (ERK) pathways, resulting in increased cancer cell survival and proliferation. Cancer cells have high densities of the EGFR, HER2, and HER3 causing phosphorylation of tyrosine amino acids on protein substrates and tyrosine amino acids near the C-terminal of the RTKs. After transforming growth factor (TGF) & alpha; binds to the EGFR, homodimers or EGFR heterodimers form. HER2 forms heterodimers with the EGFR, HER3, and HER4. The EGFR, HER2, and HER3 are overexpressed in lung cancer patient tumors, and monoclonal antibodies (mAbs), such as Herceptin against HER2, are used to treat breast cancer patients. Patients with EGFR mutations are treated with tyrosine kinase inhibitors, such as gefitinib or osimertinib. Peptide GPCRs, such as NTSR1, are present in many cancers, and neurotensin (NTS) stimulates the growth of cancer cells. Lung cancer proliferation is impaired by SR48692, an NTSR1 antagonist. SR48692 is synergistic with gefitinib at inhibiting lung cancer growth. Adding NTS to lung cancer cells increases the shedding of TGF & alpha;, which activates the EGFR, or neuregulin-1, which activates HER3. The transactivation process is impaired by SRC, matrix metalloprotease, and reactive oxygen species inhibitors. While the transactivation process is complicated, it is fast and occurs within minutes after adding NTS to cancer cells. This review emphasizes the use of tyrosine kinase inhibitors and SR48692 to impair transactivation and cancer growth.