Expression of C-Terminal Modified Serine Palmitoyltransferase-1 Alters Chemosensitivity of Inflammation-Associated Human Cancer Cell Lines

Abstract

Background: The human serine palmitoyltransferase-1, SPTLC1, subunit is emerging as a stress responsive protein with putative role in modulating cellular stress response behavior. When compared to the parental cell line, recombinant Glioma cells expressing C-terminal modified SPTLC1 are found to show resistance to the cytotoxic effect of polycyclic hydrocarbons, PHs, including the environmental contaminant 3-methylcholanthrene. This novel functional association of SPTLC1 expression with proliferative capacity is thought to be due, in part, to its ability for crosstalk with protein regulators of different biological processes. Whether the effect of SPTLC1 on sensitivity to PHs extends to therapeutic drugs and the progression of the malignant phenotype is of research interest. Methods: In the current study, sub-cellular localization was by immunostaining for SPTLC1 in untreated and chemical treated cells and detection with confocal microscopy. The effect expressing C-terminal modified SPTLC1, in cancer cell lines of the inflammation-associated type, has on chemosensitivity and gene expression was also assessed. Parent Glioma LN18 and SKN-SH cells and their SPTLC1 recombinants were each treated with Glutamate, an excitatory neurotransmitter that can participate in both neuronal and excitotoxic signaling. In addition to the Glioma and SKN-SH cells, the PC3 prostate cancer and 647V bladder cancer cell lines were also treated with Celecoxib, a potent inhibitor of cyclooxygenase 2, COX-2, and an anti-inflammatory drug recently found to have anti-neoplastic activity against several malignancies. Results: Confocal microscopy revealed that Celecoxib mediates both rapid and enhanced redistribution of SPTLC1 and COX-2, to focal adhesion sites. In cell viability assay, SPTLC1 recombinant cells exhibited differential but dose-dependent resistance to excitotoxic levels of Glutamate. Drug co-treatment with a non-lethal dose of the potent kinase inhibitor, Sulfasalazine, increased the anti-proliferation effect of Celecoxib in a dose-dependent manner for all the cell lines tested. Conclusions: The effect of SPTLC1 expression on cellular chemosensitivity seen in the present study further highlights possible role of a C-terminal modified SPTLC1 variant in the biologic modulation of cellular behavior in response to therapeutic anticancer drugs.