To date, there are many tumor-associated glycoproteins that are found and should be used for clinical diagnosis, including alpha-fetoprotein, prostate acid phosphatase, carcinoembryonic antigen, alpha antitrypsin, and thyroglobulin l.
Prostate acid phosphatase
Prostate acid phosphatase is a glycoprotein that hydrolyzes phosphate esters in prostatic secretions. In prostate cancer, the level of PAP in serum increased significantly, and the degree of increase was basically parallel to the condition of prostate cancer. PAP is of little significance for the early diagnosis of prostate cancer, but it is of great significance for monitoring the treatment effect, recurrence, metastasis and prognosis of prostate cancer. In prostate cancer, the serum PAP concentration increased significantly, and the degree of increase was basically parallel to the development of cancer. When the condition improves, the PAP level decreases; when it rises again, it often indicates that the cancer has recurrence, metastasis, and poor prognosis.
Figure 1. Protein structure of prostate acid phosphatase.
Alpha-fetoprotein (AFP) is a glycoprotein that belongs to the albumin family and is mainly synthesized by fetal liver cells and yolk sacs. Alpha-fetoprotein has a higher concentration in the fetal blood circulation and decreases after birth. The fetoprotein is basically replaced by albumin from 2 to 3 months after birth. Alpha-fetoprotein has many important physiological functions, including transport functions, two-way regulatory functions as growth regulators, immunosuppression, and T lymphocyte-induced apoptosis. Alpha-fetoprotein is closely related to the occurrence and development of liver cancer and a variety of tumors, and it can show a higher concentration in a variety of tumors, which can be used as a positive detection index for a variety of tumors. At present, it is mainly used as a serum marker of primary liver cancer in clinical practice for the diagnosis and monitoring of the efficacy of primary liver cancer.
Figure 2. Protein structure of Alpha-fetoprotein (AFP).
Carcinoembryonic antigen (CEA)
Carcinoembryonic antigen (CEA) is a tumor-associated antigen first extracted from colon cancer and embryonic tissues by Gold and Freedman in 1965. It is an acidic glycoprotein with the characteristics of human embryonic antigens. The surface of differentiated cancer cells is a structural protein of the cell membrane. It is formed in the cytoplasm, is secreted extracellularly through the cell membrane, and then enters the surrounding body fluids. Therefore, it can be detected from serum, cerebrospinal fluid, breast milk, gastric juice, pleural and ascites fluid, urine, and feces.
Figure 3. Protein structure of carcinoembryonic antigen (CEA).
Antitrypsin is a glycoprotein. 10% -20% sugar, mainly synthesized by the liver. It has a molecular weight of 5.6kD and a half-life of 5.6 days in vivo. It is the main component of α1-globulin on conventional protein electrophoresis. Its biological function is to inhibit trypsin, chymotrypsin, hyaluronidase, plasmin, elastase, etc., and it also inhibits other enzymes such as thrombin and urokinase. It is a broad-spectrum protease inhibitor. It is also an acute phase response protein. In inflammatory diseases, alpha antitrypsin can enter the tissue fluid through capillaries, and the concentration is often high in the inflammation area, which has a certain limiting effect on acute inflammatory diseases.
Figure 4. Protein structure of Alpha-Antitrypsin.
Thyroglobulin (Tg) is a large molecular glycoprotein secreted by thyroid follicular epithelial cells. Most of them are synthesized by thyroid cells and released into the remnant cavity of thyroid follicles. Factors such as TSH, iodine deficiency in the thyroid gland, and thyroid-stimulating immunoglobulin can stimulate its production. In patients with congenital hypothyroidism, detecting Tg can identify complete thyroid defects and hypothyroidism. Thyroglobulin is also considered a special marker of thyroid body integrity. It is a tumor marker of differentiated thyroid cancer (DTC) and can be used as an important reference index for patients with differentiated thyroid cancer after treatment. It can also be used to distinguish between subacute thyroiditis and pseudothyroidism.
Figure 5. Thyroid hormone synthesis.