Proton IDE V18.104.22.168 Full Version
GLIC is a bacterial ligand-gated ion channel (pLGIC) capable of detecting extracellular protons, and of being activated by acidic pH. To identify the proton activation locus and the specific amino acids responsible for proton sensing, we focused on GLIC histidine residues, as these side chains are known to play a central role in H+ sensing in pentameric ligand-gated ion channels (pLGIC) [ 1 – 4 ]. GLIC was analyzed using alanine-scanning mutagenesis with electrophysiology in oocytes, to test the contribution of conserved histidine residues in relation to its pH-induced activation. Wild-type GLIC (GLICwt) exhibits robust responses to protons (pH50 = 5.01), low pH, and acidic pH (3.9), with an EC50 of 4.1.2. GLIC His118 is essential to activation, a fact that may be related to the main reason of its localization, as it is one of the conserved residues in the H4-helix of the second transmembrane domain (TMD) of pLGICs [ 5 ]. However, although His231 is an important residue in GLIC activation, it is dispensable in signal transduction. We extended our study to 19 other histidines, of which 13 are conserved in GLIC, and to all other conserved residues in the ECD, to test their role in GLIC activation. This analysis reveals that histidines are crucial for GLIC activation, and further that E35 in the TMD and His118, His236, and H235 in the second TMD helix are key proton sensing amino acids in proton activation of GLIC, with His231 and His222 at the interface between the ECD and the first TMD as minor contributors. Finally, our mutational analysis reveals that His231 plays a key role in the gating process, as its neutralization abolishes the pH sensitivity of GLIC.
Our results demonstrated that targeted proton therapy can be an effective method of treating a variety of uterine tumors. However, a new primary tumor is diagnosed in one out of three patients. Further studies are required to assess the long-term risks and benefits of the treatment. Specifically, it will be critical to follow these patients for a prolonged period of time in order to assess if the tumors recur within or outside the treatment field. In our study, four of the six patients with recurrent tumors developed contralateral malignant cancer and four of the five patients with recurrent tumors were over age 40. None of the patients developed a second uterine malignancy.
In 2014, the American Society for Radiation Oncology recommended that patients with a large uterine or cervical tumor should be considered for proton therapy, while patients with a small cervical or endometrial tumor should be considered for brachytherapy alone, or brachytherapy followed by chemotherapy or radiation therapy . In our study, all but one of the six patients with a large tumor had a complete response. The three patients with a large, FIGO stage 2–3 cervical or endometrial tumor were all FIGO stage 1 at the time of recurrence. One patient was found to have cancer outside the uterine corpus and cervix at the time of recurrence. Another patient had a Stage IIIb tumor and was found to have a small ovarian metastasis at the time of recurrence. All patients with recurrent, unresectable tumors were treated with HDR brachytherapy. Future studies with longer follow-up are warranted to determine if the risk of a second malignancy will increase as the follow-up period increases.