Expression of Human Tissue Kallikreins (KLKs) in Polymorphous Low Grade Adenocarcinoma (PLGA)

Abstract

Polymorphous low grade adenocarcinoma (PLGA) is the second most common malignant salivary gland tumour of the minor salivary glands. Human tissue kallikreins (KLKs) are a family of highly conserved serine proteases expressed by various tissues throughout the body. KLKs have become powerful tumour markers for the diagnosis of the cancer patient (e.g. PSA (KLK3)). The literature demonstrates a link between KLKs and salivary gland neoplasms. The purpose of this study is to determine levels of KLK mRNA in tissue samples of formalin fixed paraffin embedded polymorphous low grade adenocarcinoma (PLGA). Secondly, we wish to determine if KLK expression is limited to tumour cells alone.Nineteen cases of PLGA were reviewed . A diagnosis of PLGA was confirmed, demographic data was collected, and formalin fixed paraffin-embedded PLGA and normal salivary gland tissue samples were obtained. RNA isolation was achieved, followed by conversion to complementary DNA via reverse transcription. Synthesized DNA primers were added to target kallikrein DNA and through PCR, the quantitative level of expression of KLKs 1-15 was recorded. Samples exhibiting high and low KLK expression were selected for immunohistochemistry staining, using a standard protocol.Results from PCR data reveals statistically significant increase in the mean KLK mRNA expression for KLK1, KLK4, KLK10, KLK12 and KLK15 in PLGA tissue samples, as compared with normal salivary gland tissue (Mann Whitney U test, p<0.05).Immunohistochemistry results demonstrate tumour specific staining. Notably, all samples demonstrating relatively higher KLK mRNA expression showed equivalent or increased staining grade scores relative to the low KLK mRNA expression samples, with respect to a specific KLK.In tissue samples of polymorphous low grade adenocarcinoma there is an increase of KLK1, KLK4, KLK10, KLK12 and KLK15 mRNA relative to normal salivary gland tissue. Furthermore, the tumour cells stain positively and specifically for kallikreins.