The Study Of Human LDH-C As Potential Target For Lung Cancer Therapy

Lactate dehydrogenase(LDH)is an important terminal enzyme that catalyzes the conversion of pyruvate and lactic acid by the glycolytic pathway,and Generate NAD~+.It plays an important role in energy metabolism of tumors.There are three isozymes in animals,namely LDH-A4,LDH-B4 and LDH-C4.LDH-C4 is a sperm-specific lactate dehydrogenase,which is considered to be a cancer-testis antigen(CTA)in recent years,is actively expressed in many tumors.However,the biological function of LDH-C4 in tumor still remains largely unknown.In view of such situation,the expression of LDH-C in lung cancer tissue was detected by tissue microarray.Then,Knocked-down of LDH-C in A549 cell by use si RNA,and were verified by q RT-PCR,MTT and flow cytometry.To further study the function of LDH-C in cancer cells,a stable cell line of A549 that overexpress LDH-C was constructed and inoculated subcutaneously in nude mice.Finally,the three isoenzyme proteins of LDH were constructed and purified,and the enzyme properties were analyzed to lay the foundation for further exploration of the role of LDH-C in tumors.The results show that high expression of LDH-C in patients with lung cancer,and can promote the growth of tumor.LDH-C can significantly inhibit the survival and proliferation,indicating that LDH-C can be used as a potential target for tumor treatment.Kinetic analysis showed that LDH-C4 has higher binding affinity and catalytic efficiency both for NADH and pyruvate among the three isoforms.Tumor cells mainly use aerobic glycolysis as the main energy metabolism method.NAD~+is the key to the continued glycolysis.The high affinity and high catalytic efficiency of LDH-C4 for NADH and pyruvate can meet this requirement.In addition,the pH optimum determination shows that LDHC4 has a pH value of 7.5 compared to 8.2 of both LDHA4 and LDHB4.LDHC4 also show the highest activities at the pH range of 6.4 to 7.6 among the three LDH isoforms.Thermal stability assay showed that LDHC4 was much more thermally stable than LDHA4 and LDHB4.Therefore,we believe that LDH-C is promising as a target for tumor therapy.