DEC2 negatively regulates VEGF expression in oral squamous cell carcinoma

Abstract

Objectives: DEC1 (BHLHB2/Sharp2/Stra13) and DEC2 (BHLHB3/Sharp1) are basic-helix-loop-helix (bHLH) transcription factors, involved in cellular differentiation, responses to hypoxia, and circadian rhythms. It is well established that the expression of vascular endothelial growth factor (VEGF) is upregulated by hypoxia, and the expression of VEGF in response to hypoxia depends on transcriptional activation by a heterodimer comprising hypoxia-inducible factor 1 alpha (HIF-1alpha) and arylhydrocarbon receptor nuclear translocator 1 (ARNT1). We recently showed that DEC2, but not DEC1 suppressed VEGF gene expression under hypoxic conditions. DEC2 protein was co-immunoprecipitated with HIF-1alpha but not with ARNT1. The binding of HIF-1alpha to the hypoxia response element (HRE) in the VEGF promoter was decreased by DEC2 overexpression, and increased by DEC2 knockdown. We also showed that the circadian expression of VEGF showed a reciprocal pattern to that of DEC2 in cartilage. DEC2 had a circadian oscillation in implanted Sarcoma 180 cells. However, the functions of these two factors in oral squamous cell carcinoma have not been elucidated in detail.

Methods: Reverse transcription-polymerase chain reaction (RT-PCR), siRNA and real-time RT-PCR, Western blot analysis, and immunohistochemistry were performed.

Results: We found a significant correlation between the circadian expression of DEC2 and VEGF expression in carcinomas.

Conclusion: We conclude that DEC2 negatively regulates VEGF expression in oral squamous cell carcinoma and plays an important role in the pathological conditions in which VEGF is involved.