HYAL1(LUCA-1), a candidate tumor suppressor gene on chromosome 3p21.3, is inactivated in head and neck squamous cell carcinomas by aberrant splicing of pre-mRNA

The hyaluronidase first isolated from human plasma, Hyal-1, is expressed in many somatic tissues. The Hyal-1 gene, HYAL1, also known as LUCA-1, maps t o chromosome 3p21.3 within a candidate tumor suppressor gene locus defined by homozygous deletions and by functional tumor suppressor activity. Hemizy gosity in this region occurs in many malignancies, including squamous cell carcinomas of the head and neck, We have investigated whether cell lines de rived from such malignancies expressed Hyal-1 activity, using normal human keratinocytes as controls. Hyal-1 enzyme activity and protein were absent o r markedly reduced in six of seven carcinoma cell lines examined. Comparati ve genomic and fluorescence ill situ hybridization identified chromosomal d eletions of one allele of HYAL1 in six of se, en cell lines. Initial RT-PCR analyses demonstrated marked discrepancies between levels of HYAL1 mRNA an d protein. Despite repeated sequence analyses, no mutations were found, How ever, two species of transcripts were identified when primers were used tha t included the 5' untranslated region. The predominant mRNA species did not correlate with protein translation and contained a retained intron, A seco nd spliced form lacking this intron was found only in cell lines that produ ced Hyal-1 protein. Inactivation of HYAL1 in these tumor lines is a result of incomplete splicing of its pre-mRNA that appears to be epigenetic in nat ure.