Upregulation of thromboxane synthase in human colorectal carcinoma and the cancer cell proliferation by thromboxane A₂

Tumor growth of colorectal cancers accompanies upregulation of cyclooxygenase-2, which catalyzes a conversion step from arachidonic acid to prostaglandin H₂ (PGH₂). Here, we compared the expression levels of thromboxane synthase (TXS), which catalyzes the conversion of PGH₂ to thromboxane A₂ (TXA₂), between human colorectal cancer tissue and its accompanying normal mucosa. It was found that TXS protein was consistently upregulated in the cancer tissues from different patients. TXS was also highly expressed in human colonic cancer cell lines. Depletion of TXS protein by the antisense oligonucleotide inhibited proliferation of the cancer cells. This inhibition was rescued by the direct addition of a stable analogue of TXA₂. The present results suggest that overexpression of TXS and subsequent excess production of TXA₂ in the cancer cells may be involved in the tumor growth of human colorectum.