Distribution of Thioredoxin Peroxidases and Expression of Thioredoxin Peroxidases in Various Human Cancers

Objectives: Thioredoxin peroxidase(TPx), which does not exhibit similar activity and amino acid sequence homology to conventional antioxidant enzymes has been purified from S cerevisiae and bovine brain. Natural killer enhancing factor-A(NKEF-A)/ proliferation associated gene(PAG), natural killer enhancing factor-B(NKEF-B)/TPx and MER5 which has sequence homology to yeast TPx has been recently characterized biochemically. Prosperi has reported that the level of PAG in HL-60 cells was increased after serum stimulation and decreased after differentiation induced by DMSO treatment. It is well known that thioredoxin, the electron donor to thioredoxin peroxidase, also implicated in cell proliferation via protein kinase C pathway. Disturbed balance of reactive oxygen species and antioxidant in tumor tissue could enhance the cancer promotion. This study was designed to investigate the distribution of NKEF-A/FAG, NKEF-B/TPx and MER5 in various tissues, and the expression of NKEF- A/PAG, NKEF-B/TPx and MER5 in human cancers. Methods: We used antibodies against the puri- fied recombinant protein of NKEF-A/PAG and NKEF-B/TPx and C-terminus amino acids(SP- TASKEYFEKVHO) of MER5, We separated cytosole and mitochondria from rat liver and prepared crude extract from these. We prepared crude extract of various tissues from rat and cancer tissue from lung, stomach and breast and paired normal tissue. Immunoblot analysis of these crude extracts was performed. Results: 1) NKEF-A/PAG and NKEF-B/TPx existed in cytosolic fraction as Cu, Zn-SOD and MER5 mainly exist mainly in mitochondrial fraction as Mn-SOD. Although the level of NKEF-AIPAG, NKEF-B/TPx and MER5 was different, all tissues exhibited NKEF-A/PAG, NKEF-B/TPx and MER5 immunoreactive bands. The adrenal gland had relatively strong band of MER5. 2) The expression of NKEF-A/PAG in HL-60 cell was increased after serum stimulation and decreased after cell differentiation induced by DMSO treatment. 3) The expression of NKEF-A/PAG was increased in lung and breast cancer tissues compaired to paired normal tissues but was not changed in stomach cancer tissues and the expression of NKEF-B/TPx and MER5 was not changed in lung, stomach and breast cancer tissues compaired to paired normal tissues. 4) The level of NKEF-A/PAG, NKEF-B/TPx and MER5 was not different among various lung cancer cell lines. Conclusion: The NKEF-A/PAG, NKRF-B/TPx and MER5 are present in the cytosol and mitochondria of various tissues. The NKEF-A/PAG, in particular, is associated with cell proliferation and differentiation and overexpressed in lung and breast cancer.ope