ABSTRACT
L-Dopa decarboxylase (DDC) catalyzes the decarboxylation of L-Dopa to dopamine and 5-hydroxytryptophan (5-HTP) to serotonin. Although DDC has been purified from a variety of peripheral organs, including the liver, kidney and pancreas, the physiological significance of the peripherally expressed enzyme is not yet fully understood. DDC has been considered as a potential novel biomarker for various types of cancer, however, the role of DDC in the development of hepatocellular carcinoma (HCC) remains to be evaluated. Phosphatidylinositol 3-kinase (PI3K), on the other hand, has been shown to play a key role in the tumorigenesis, proliferation, metastasis, apoptosis, and angiogenesis of HCC by regulating gene expression. We initially identified the interaction of DDC with PI3K by means of the phage display methodology. This association was further confirmed in human hepatocellular carcinoma cell lines, human embryonic kidney cells, human neuroblastoma cells, as well as mouse brain, by the use of specific antibodies raised against DDC and PI3K. Functional aspects of the above interaction were studied upon treatment with the DDC inhibitor carbidopa and the PI3K inhibitor LY294002. Interestingly, our data demonstrate the expression of the neuronal type DDC mRNA in HCC cells. The present investigation provides new evidence on the possible link of DDC with the PI3K pathway, underlining the biological significance of this complex enzyme.