Klotho _ LRP-6 _ Gastric Adenocarcinoma

Overview

Gastric cancer is the fifth most common malignancy in the world after cancers of the lung, breast, colorectum, and prostate. Gastric cancer is the third leading cause of cancer death and is responsible for 723,000 deaths yearly. Gastric carcinoma (GC) is a multifactorial disease which is difficult to diagnose in early-stage because of a time lag between the onset of growth and the appearance of clinical presentation. So, its prognosis is poor as evidenced by the 5-year survival rate. Klotho is anti-aging gene encoding a protein with multiple pleiotropic effect. Cancer and ageing share comparable principles. Klotho gene has been described as a tumor suppressor gene in numerous solid tumors and hematological malignancies. Klotho expression has been shown to be significantly down-regulated in malignant tissue compared to adjacent non-malignant tissue with good prognosis in cancers with high Klotho expression, including colorectal, pancreatic, gastric, esophageal, breast, hepatocellular, ovarian, and renal carcinomas. In contrast, a recent study documented that Klotho negative invasive duct carcinoma group exhibited good prognosis than the Klotho positive group regarding the disease- free survival after the surgical resection in breast cancer patient. Lipoprotein receptor- related protein 6 (LRP6) is a type I single transmembrane protein which is a member of the low-density lipoprotein receptor (LDLR) gene family of receptors that is highly conserved among species. In 2000, LRP6 was identified as a co-receptor for Wnt and Frizzled (FZD) to transduce Wnt/β-catenin signaling. Dysregulation of LRP6 is involved in cancer. LRP6 is highly expressed in several cancer cell lines and overexpression of LRP6 promotes cancer cell proliferation. LRP6 expression is frequently upregulated in breast cancer tissue, and respective overexpression or knockdown of LRP6 induces or inhibits breast tumorigenesis. LRP6 is highly expressed in tumors of liver cancer patients, and overexpression of LRP6 promotes liver cancer cell proliferation and tumor growth. In prostate cancer, high expression levels of LRP6 are detected which activate Wnt/β-catenin signaling and glycolysis through Akt signaling. The end result is increased prostate cancer cell proliferation. The mechanism of Klotho-mediated Wnt inhibition was as a result of Klotho binding to Wnt ligands, namely Wnt3A and Wnt5A; thereby impeding binding of these ligands to their cell surface receptor.

Gastric cancer is the fifth most common malignancy in the world after cancers of the lung, breast, colorectum, and prostate. Gastric cancer is the third leading cause of cancer death and is responsible for 723,000 deaths yearly \[1\]. Gastric carcinoma (GC) is a multifactorial disease, where many factors can influence its development, both genetic and environmental such as infection with Helicobacter pylori (which is the main risk factor), gastric ulcer disease, gastroesophageal reflux disease and obesity \[2\]. Furthermore, genetic variations in proinflammatory and anti-inflammatory cytokine genes also influence the individual response to carcinogenic exposures. Host genetic factors are emerging as key determinants of disease risk for many cancers \[1\]. Gastric carcinoma is difficult to diagnose in early-stage because of a time lag between the onset of growth and the appearance of clinical presentation. Early symptoms of gastric cancer are not specific; as a result, most patients with early gastric cancer present with symptoms indistinguishable from benign peptic ulcer disease and, subsequently, these patients have been diagnosed at an advanced stage GC \[1\]. So, its prognosis is poor as evidenced by the 5-year survival rate and because most cases are already metastatic when diagnosed \[2\]. GC mostly affects older people. The average age of people when they are diagnosed with gastric cancer is 68 years \[1\]. Klotho is anti-aging gene encoding a protein with multiple pleiotropic effects, discovered in 1997 by Kuro-o and colleagues. The Klotho family of proteins consists of three members: α-Klotho, β-Klotho and γ-Klotho. All three are single-pass transmembrane proteins. The α-Klotho gene is composed of five exons, in humans, mice and rats expressed predominantly in the distal convoluted tubule (DCT) cells of the kidney in addition to a lesser expression in the proximal convoluted tubule (PCT) cells \[3\]. Cancer and ageing share comparable principles; the time-dependent accumulation of DNA damage is a contributing factor in ageing and also drives cancer progression. DNA damage, alongside genomic instability, is an established hallmark of most cancers. These pathways influence a number of capabilities acquired by cancer cells including the ability to evade apoptosis, cause tumor invasion and metastasis, sustain angiogenesis, and facilitate unlimited cellular replicative potential. Alpha-Klotho potentially influences these phenotypes through the inhibition of a number of signaling pathways such as insulin-like growth factor 1 receptor (IGF-1R), fibroblast growth factor (FGF), transforming growth factor β (TGFβ) and wingless-related integration site (Wnt) \[4\]. Klotho gene has been described as a tumor suppressor gene in numerous solid tumors and hematological malignancies, Klotho represents a possible therapeutic target for patients with these diseases, the majority of whom have limited treatment options \[5\]. Klotho expression has been shown to be significantly down-regulated in malignant tissue compared to adjacent non-malignant tissue with good prognosis in cancers with high Klotho expression, including colorectal \[6\], pancreatic \[7\], gastric \[8\], esophageal \[9\], breast \[10\], hepatocellular \[11\], ovarian \[12\], and renal carcinomas \[13\]. In contrast, a recent study done by Suzuki et al, 2021 documented that Klotho negative invasive duct carcinoma group exhibited good prognosis than the Klotho positive group regarding the disease- free survival after the surgical resection in breast cancer patient \[14\]. Lipoprotein receptor- related protein 6 (LRP6) is a type I single transmembrane protein which is a member of the low-density lipoprotein receptor (LDLR) gene family of receptors that is highly conserved among species. In 2000, LRP6 was identified as a co-receptor for Wnt and Frizzled (FZD) to transduce Wnt/β-catenin signaling. The extracellular domain of LRP6 interacts with Wnt and activates Wnt/β-catenin signaling at the plasma membrane. LRP6 with a truncated extracellular domain is constitutively active and can potentiate Wnt/β-catenin signaling independently of Wnt. Dysregulation of LRP6 is involved in cancer. LRP6 is highly expressed in several cancer cell lines and overexpression of LRP6 promotes cancer cell proliferation \[15\]. LRP6 expression is frequently upregulated in breast cancer tissue, and respective overexpression or knockdown of LRP6 induces or inhibits breast tumorigenesis \[16\]. LRP6 is highly expressed in tumors of liver cancer patients, and overexpression of LRP6 promotes liver cancer cell proliferation and tumor growth \[17\]. In prostate cancer, high expression levels of LRP6 are detected which activate Wnt/β-catenin signaling and glycolysis through Akt signaling. The end result is increased prostate cancer cell proliferation \[19\]. The mechanism of Klotho-mediated Wnt inhibition was as a result of Klotho binding to Wnt ligands, namely Wnt3A and Wnt5A; thereby impeding binding of these ligands to their cell surface receptor \[4\]. Klotho has also been shown to increase the efficacy of chemotherapy, including cisplatin in human lung cancer by modulating the phosphatidylinositol 3-kinase/protein kinase B PI3K/Akt pathway, indicating that Klotho therapy may be effective in combination with existing cancer therapies \[4\]. To our knowledge, it is the first research to study the expression of Klotho and LRP-6 protein in gastric adenocarcinoma by immunohistochemistry.