The study was aimed to understand the importance of the hedgehog signaling pathway in development of head and neck squamous cell carcinoma (HNSCC).
The molecular profiles of the key regulatory genes of the pathway were analysed in the adjacent normal epithelium and tumor samples. The findings were validated in HNSCC cell line.
In the bioinformatical analysis, severe reduction in the expression of HHIP was evident in the datasets. The protein and mRNA expression studies in our sample pool revealed interplay of various isoforms of PTCH1 gene (PTCH1-1 and 1B) together with high/medium expression of GLI, SHH, SMO and HHIP in the basal/parabasal layers of the normal epithelium. As the disease progressed, severe downregulation of HHIP coupled with upregulation of GLI1 and differential expression pattern of various PTCH1 gene isoform was evident. Promoter methylation analysis of PTCH1 gene revealed the involvement of more than one promoter of PTCH1 in regulating the expression of different isoform of this gene during tumorigenesis. Treating the FaDu cell line with the demethylating agent 5-aza-2′-deoxycytidine reversed the methylation effects of HHIP and PTCH1 and de-activated the pathway. Also, reduced expression of HHIP-AS1 was observed in our sample pool suggesting multiple ways of regulation of the HHIP gene. Lastly, the patients with under expression of HHIP, HHIP-AS1, high expression of GLI1 showed worse five-year over-all survival trend.
Dynamic promoter switching of PTCH1 and frequent inactivation of HHIP are the key regulatory events of hedgehog pathway activation in HNSCC.

Copyright © 2022 Elsevier GmbH. All rights reserved.