Resarch Interests:
Identification of Functional Promoter Regions of Two Human DihydroCeramide Synthase (CerS/LASS) Genes: Mechanisms of Its Regulation by Chemotherapeutic Agent Imatinib in Head and Neck Cancer Cells (HNSCC)
The human longevity assurance gene 1 (LASS1) encodes for dihydroceramide synthase 1 (dhCerS1), and generates C18-ceramide in the de novo ceramide synthesis pathway; while dihydroceramide synthase 6 (dhCerS6) generates C16-ceramide via the de novo pathway. Our preliminary data showed that dhCerS1 and thus endogenous C18-ceramide is down-regulated in HNSCC, and upon treatment with chemotherapeutic agents, such as gemcitabine/doxorubicin or Imatinib (Gleevec), dhCerS1/LASS1 mRNA is up-regulated, leading to apoptosis.
Conversely, dhCerS6/C16-ceramide is up-regulated in HNSCC, correlating with an increase in cellular proliferation in HNSCC cells. Thus, the mechanisms, which activate and repress dhCerS1/LASS1 and dhCerS6/LASS6, respectively, need to be elucidated to understand their roles in cancer apoptosis and proliferation.
Here we have cloned the functional dhCerS1 (~1550bp) and dhCerS6 promoters
(~1600bp) that regulate their expression. We also characterized the minimal core promoter regions of each gene in various HNSCC cell lines. These regions correspond to -300 to -80 bp upstream of the +1 start site for dhCerS1, and -800 to -1bp upstream of the +1 start site for dhCerS6. Screening various chemotherapeutic agents, fatty acids, and sphingolipid compounds revealed that treatment with Imatinib strongly induce the promoter activity of dhCerS1/LASS1 and not dhCerS6/LASS6 in HNSCC cells. Specifically, Imatinib up-regulated the full length dhCerS1 promoter by about 2.5-fold, and the minimal core promoter by approximately 10-fold, leading to the up-regulation of its mRNA expression in these cells. Motif searches of the core promoter region in the dhCerS1 promoter showed the presence of multiple SP1/SP3 and AP2 transcription factor binding sites. Currently, RNAi knock down studies of these two transcription factors are being performed to elucidate the mechanisms of activation of the
dhCerS1/LASS1 promoter in response to Imatinib in HNSCC cells. In summary, preliminary data shows promising future directions to elucidate the molecular mechanisms which mediate the up-regulation of dhCerS1 transcription, specifically inducing apoptosis, in HNSCC cells.
|
