Kallikrein gene expression in human pituitary tissues

Abstract

Objective: The glandular kallikreins are a family of enzymes involved in the post-translational processing of polypeptides. Three family members have been characterized in the human: glandular kallikrein (KLK1) and two genes expressed in the prostate, KLK2 or hGK1 and KLK3 or prostate specific antigen (PSA). Both kallikrein immunoreactivity and KLK1 mRNA have been detected in the rat anterior pituitary and oestrogen induced prolactinomas. Immunoreactive kallikrein has also been reported in prolactin secreting pituitary tumours in humans. In this study we wished to determine whether KLK1 and/or other KLK genes were expressed in human pituitary tumours.

Design and patients: Retrospective analysis of KLK gene expression in pituitary tissue obtained at surgery from 11 patients with a range of pituitary syndromes, 10 of which were tumour induced and included four prolactinomas. Three normal pituitaries, obtained at necropsy, were also analysed.

Measurements: Pituitary total RNA was subjected to both Northern blot analysis, with KLK1 and KLK2 cDNA probes, and KLK-specific reverse transcriptase -- polymerase chain reaction (RT-PCR).

Results: No KLK1 gene expression was detected on Northern blot analysis although expression of PRL, GH and pro-opiomelanocortin (POMC) was variously detected. KLK RT-PCR coupled with Southern blot analysis using oligonucleotide probes specific for each of the three KLK genes was positive in many tumours but with varying levels and differential expression. Overall, KLK1 was the most abundant with KLK3 the least. The identity of KLK1 and KLK2 was confirmed by sequencing the PCR products. There was no obvious correlation between KLK1 and hormone gene expression; KLK1 was present in PRL positive and negative tumours and in normal pituitary tissue.

Conclusions: We have demonstrated a low level of expression of KLK1 as well as KLK2 and KLK3 in the human pituitary. The expression of KLK2 and KLK3 in the pituitary is a novel finding. The lack of correlation between PRL and KLK1 gene expression is an unexpected finding suggesting that the interaction between these factors may be more complex in the human pituitary than in the rodent model.