Analysis of the FHIT gene and its product in squamous cell carcinomas of the head and neck

The FHIT gene has been implicated as a tumor suppressor gene in human malignancies. To determine if FHIT alterations play a role in human squamous cell carcinogenesis of the head and neck (HNSCC), we examined the gene and its product by RT-PCR, SSCP, Northern, Southern, and Western blot analysis in primary HNSCC and/or HNSCC cell lines. Three of 32 tumor samples lacked detectable expression of FHIT by RT-PCR but showed amplification of a control gene of similar size. One of 29 primary tumors and 2/9 HNSCC cell lines exhibited aberrant transcripts generated by RT-PCR methods using one set of 40 cycles of amplification. FHIT mRNA expression was absent in seven HNSCC cell lines but detectable in primary keratinocytes by Northern analysis. Using specific polyclonal antiserum to the full-length FHIT protein in immunoblot analyses, 4/9 cell lines analysed showed no expression of pFhit, two exhibited low levels of expression, and three expressed a putative truncated pFhit. One of 15 tumors analysed also exhibited an overexpressed truncated protein. PCR/SSCP and Southern analysis of one cell line DNA that expressed a truncated protein indicated that it sustained homozygous loss of FHIT exon 5. Our results suggest that alterations in FHIT at the DNA, RNA, and protein levels exist at a low but significant frequency in HNSCCs. Further studies regarding the potential biological activity of FHIT are needed to clarify the role of this gene in HNSCC tumorigenesis.