Expression analysis of cyclins in pituitary adenomas and the normal pituitary gland

OBJECTIVES The molecular events involved in pituitary tumour development ar e still poorly understood. The cyclins play an important role in the contro l of the cell cycle during cell proliferation and over-expression of the cy clins has been shown in many different tumour types. The aim of this study was to investigate whether, in comparison to the normal gland, ectopic expr ession of cyclins occurs in pituitary tumours, and whether differences in c yclin expression are seen with different pituitary tumour types or in assoc iation with different tumour behaviour. In contrast to work on cyclin D the re are no published data on cyclin B, A and E in human pituitary tumours, METHODS Sixty-seven surgically removed pituitary tumours and 10 specimens o f normal human anterior gland were studied using immunohistochemistry to de tect the nuclear expression of cyclin A, a, D and E. The microvascular dens ity las a measure of angiogenesis), Ki-67 labelling index (10 assess cell p roliferation) and bcl-2 expression had previously been investigated in this cohort, RESULTS All tumours studied contained cells that immunostained positively f or cyclin A, a, D and E, However the proportion of positive cells in each t umour type was different. In contrast, there were no cyclin D positive cell s in the normal anterior pituitary gland studied, and labelling indices (LI ) for cyclins A, B and E were significantly lower in the normal gland than in pituitary adenomas. The cyclin LIs for A, B, D and E were significantly higher in macroadenomas when compared to microadenomas. Non-functioning pit uitary tumours (NFA) generally showed the highest cyclin LI. In particular, both recurrent and nonrecurrent NFA showed significantly higher cyclin D L I than other tumours, The ratio of cells expressing cyclin a compared to th ose expressing cyclin A was significantly higher in functionless tumours th at regrew when compared to NFAs that did not (P<0.05). Cyclin D LI and the overall Ki-67 LI as a measure of cell proliferation were related (R-2=11.4, P=0.0033) and bcl-2 positive tumours had significantly higher cyclin D LI compared with bcl-2 negative tumours. There was a weak relationship between angiogenesis and the relative proportion of cells expressing D when compar ed to those in S phase (D/A ratio) (r(2)=10.5, P=0.02). CONCLUSIONS We have demonstrated that ectopic expression of cyclin D and ov er-expression of cyclins A, B and E, regulating different stages of the cel l cycle is common in pituitary adenomas. In addition, cyclin expression was related to size and to pituitary tumour regrowth, The differences between functionless tumours that regrow and those that do not, may be due to reduc ed bcl-2 expression, increased cell proliferation, more cells at the G2/M s tage (B/A ratio) and reduced cell differentiation with more aggressive subs equent tumour behaviour. Cyclin D expression and cell proliferation were re lated indicating that the cells entering the cycle become 'committed' to ce ll cycle progression. There was no relative over-expression of individual c yclins, and therefore no evidence of relative increase in cell cycle phase, indicating that the increased cyclin expression is more likely to be due t o constant mitogenic stimulation rather than cell cycle regulatory failure. Although nuclear cyclin expression is a good marker of tumour growth and a ggressive behaviour, the growth signal that leads to cyclin expression rema ins to be identified.