Defects in cell growth regulation by C_18:0-ceramide and longevity assurance gene 1 in human head and neck squamous cell carcinomas

In this study, endogenous long chain ceramides were measured in 32 human head and neck squamous cell carcinoma (HNSCC) and 10 nonsquamous head and neck carcinoma tumor tissues, as compared with adjacent noncancerous tissues, by liquid chromatography/ mass spectroscopy. Interestingly, only one specific ceramide, C_18:0-ceramide, was selectively down-regulated in the majority of HNSCC tumor tissues. On the other hand, in nonsquamous tumor tissues, this selectivity for C¹⁸-ceramide was not detected. These data suggested the hypotheses that decreased levels of C₁₈-ceramide might impart a growth advantage to HNSCC cells and that increased generation of C₁₈-ceramide may be involved in the inhibition of growth. These roles were examined by reconstitution of C₁₈-ceramide at physiologically relevant concentrations in UM-SCC-22A cells (squamous cell carcinoma of hypopharynx) via overexpression of mammalian upstream regulator of growth and differentiation factor 1 (mUOG1), a mouse homologue of longevity assurance gene 1 (mLAG1), which has been shown to specifically induce the generation of C ₁₈-ceramide. Liquid chromatography/mass spectroscopy analysis showed that overexpression of the mLAG1/ mUOG1 resulted in increased levels of only C_18:0-ceramide by ∼2-fold, i.e. concentrations similar to those of normal head and neck tissues. Importantly, increased generation of C ₁₈-ceramide by mLAG1/mUOG1 inhibited cell growth (∼70-80%), which mechanistically involved the modulation of telomerase activity and induction of apoptotic cell death by mitochondrial dysfunction. In conclusion, this study demonstrates, for the first time, a biological role for LAG1 and C ₁₈-ceramide in the regulation of growth of HNSCC.