Alpha-enolase

The mRNA transcript of the ENO1 gene can be alternatively translated into a cytoplasmic protein, with a molecular weight of 48 kDa, or a nuclear protein, with a molecular weight of a 37 kDa.[9][10] The nuclear form was previously identified as Myc-binding protein-1 (MBP1), which downregulates the protein level of the c-myc protooncogene.[10] A start codon at codon 97 of ENO1 and a Kozak consensus sequence were found preceding the 3' region of ENO1 encoding the MBP1 protein. In addition, the N-terminal region of the MBP1 protein it critical to DNA binding and, thus, its inhibitory function.[10]

ENO1 overexpression has been associated with multiple tumors, including glioma, neuroendocrine tumors, neuroblastoma, pancreatic cancer, prostate cancer, cholangiocarcinoma, thyroid carcinoma, lung cancer, hepatocellular carcinoma, and breast cancer.[6][9][13][14] In many of these tumors, ENO1 promoted cell proliferation by regulating the PI3K/AKT signaling pathway and induced tumorigenesis by activating plasminogen.[6][9] Moreover, ENO1 is expressed on the tumor cell surface during pathological conditions such as inflammation, autoimmunity, and malignancy. Its role as a plasminogen receptor leads to extracellular matrix degradation and cancer invasion.[9][13][14] Due to its surface expression, targeting surface ENO1 enables selective targeting of tumor cells while leaving the ENO1 inside normal cells functional.[9] Moreover, in tumors such as non-Hodgkin lymphomas (NHLs) and breast cancer, inhibition of ENO1 expression decreased tolerance to hypoxia while increasing sensitivity to radiation therapy, thus indicating that ENO1 may have aided chemoresistance.[6][11] Considering these factors, ENO1 holds great potential to serve as an effective therapeutic target for treating many types of tumors in patients.[6][11][13]

ENO1 is located on the 1p36 tumor suppressor locus near MIR34A which is homozygously deleted in Glioblastoma, Hepatocellular carcinoma and Cholangiocarcinoma.[15][16] The co-deletion of ENO1 is a passenger event with the resultant tumor cells being entirely dependent on ENO2 for the execution of glycolysis.[17][18] Tumor cells with such deletions are exceptionally sensitive towards ablation of ENO2.[17][18] Inhibition of ENO2 in ENO1-homozygously deleted cancer cells constitutes an example of synthetic lethality treatment for cancer.

ENO1 has been detected in serum drawn from children diagnosed with juvenile idiopathic arthritis.[19]

Alpha-enolase has been identified as an autoantigen in Hashimoto's encephalopathy.[20] Single studies have also identified it as an autoantigen associated with severe asthma[21] and a putative target antigen of anti-endothelial cell antibody in Behçet's disease.[22] Reduced expression of the enzyme has been found in the corneal epithelium of people suffering from keratoconus.[23][24]

CagA protein was found to activate ENO1 expression through activating the Src and MEK/ERK pathways as a mechanism for H. pylori-mediated gastric diseases.[14]

Enolase deficiency is a rare inborn error of metabolism disease, leads to hemolytic anemia in affected homozygous carriers of loss of function mutations in ENO1.[25] As with other glycolysis enzyme deficiency diseases, the condition is aggravated by redox-cycling agents such as nitrofurantoin.