Thymidine kinase 1 (TK1) is a well-studied cancer biomarker. It is commonly\nfound upregulated in the serum of cancer patients, and its levels correlate\nwith stage and grade, disease progression, and prognosis. It has recently been\nreported that TK1 localizes on the plasma cell membrane of hematological\nand solid malignancies, and not on the membrane of normal healthy cells,\nand while on the membrane, TK1 has enzymatic activity. However, the function\nof TK1 on the surface membrane is not well understood. Here, we hypothesize\nthat it may have a role in tumor invasion and migration. It has\nbeen shown that TK1 expression levels positively correlate with epithelia to\nmesenchymal transition (EMT) markers in patients with breast cancer as\nthey progress from HER2+ to triple negative breast cancer. In this study, we\nsilenced TK1 expression by siRNA and show that TK1â??s membrane expression\nis significantly downregulated at 60 hours post transfection. Using a\nMatrigel-based quantitative invasion assay, we measured cell invasion potential\nin cells either expressing or lacking TK1 on their membrane and found\nthat cells that lack TK1 on their membrane exhibit decreased invasion potential.\nThese results suggest that TK1â??s presence on the membrane may play a\nrole in invasion and cell migration in cancer.
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