Altered distribution and synthesis of laminin-5 (kalinin) in oral lichen planus, epithelial dysplasias and squamous cell carcinomas.

Laminin-5 is a glycoprotein which mediates epithelial cell adhesion to the basement membrane. This study describes the distribution and synthesis of laminin-5 in oral lichen planus, epithelial dysplasias, squamous cell carcinomas and a lymph node metastasis using immunohistochemistry and in situ hybridization. In normal oral mucosa and lichen planus, immunoreaction to the laminin-5 was seen as a thin continuous, delicate line in the basement membrane region, although slight irregularities in the thickness and intensity of the immunoreaction could be detected in some cases with lichen planus. In epithelial dysplasias, the laminin-5 staining was discontinuous and more diffuse compared to lichen planus and normal mucosa. The immunoreaction was generally extracellular, although in some cases with lichen planus and epithelial dysplasia there were a few basal epithelial cells showing cytoplasmic staining. The invasive carcinomas and the lymph node metastasis showed a striking, intense cytoplasmic, staining of the carcinoma cells along the invasive border of the neoplastic islands and in individual infiltrating carcinoma cells. Using in situ hybridization, the laminin-5 gamma 2 chain mRNA expression could not be detected in normal oral mucosa whereas, in non-dysplastic lichen planus and, more strongly, in dysplasias, there was a clear increase in the expression of laminin-5 mRNA in the basal epithelial cells. The most intensive signal was detected in the invasive front of the oral squamous cell carcinomas and the lymph node metastasis. We conclude that, in oral squamous cell carcinoma, there is altered synthesis and secretion of laminin-5 mRNA and protein. It is also evident that in dysplastic lesions of oral epithelium the synthesis and distribution of laminin-5 is abnormal.