Synthesis and degradation of basement membranes in benign and malignant salivary gland tumours. A study by in situ hybridization

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Abstract
In this study we investigated the mRNA expressions of 72 kD and 92 kD type IV collagenases, al (IV) chain of type IV collagen, and laminin Bl chain mRNAs in a set of malignant and benign salivary gland tumours and compared the results with non‐neoplastic salivary gland tissue. While only a few cases expressed 72 kD type IV collagenase mRNA or a1 (IV) chain of type IV collagen mRNA in tumour cells, 92 kD type IV collagenase and laminin mRNA synthesis could be seen in the neoplastic cells of many tumours. Stromal fibroblasts or endothelial cells demonstrated mRNA synthesis for all these proteins to a variable degree except for Warthin's tumours, in which no synthetic activity for any of the proteins could be seen. Since signals for 92 kD type IV collagenase mRNA could be seen in non‐neoplastic epithelial cells of the salivary gland, the synthesis of 92 kD type IV collagenase by tumour cells can be regarded as an intrinsic property of salivary gland epithelial cells. The pattern of mRNA synthesis for 72 kD and 92 kD type IV collagenases follows that observed in other tumours, in which the stromal cells also mainly synthesize 72 kD type IV collagenase while epithelial tumour cells more readily express 92 kD type IV collagenase mRNA. The synthesis of type IV collagenases by malignant tumours has been suggested to be of crucial importance for invasion and metastasis. The expression of both collagenases in benign tumours, such as pleomorphic adenomas, indicates that more complex mechanisms, such as disturbances in the regulation of enzyme activity, are involved in the spread and invasion of salivary gland tumours than merely the synthesis of 72 kD and 92 kD collagenases.

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