Endocrine Abstracts

The cytokine IL-6 is synthesed and released by over half of surgically removed human pituitary adenomas and by the HP75 human pituitary tumour cell line. We have previously shown that IL6 is associated with tumour invasiveness but not with Ki67, a marker of cell proliferation. Membrane IL6R (mIL6R) has been demonstrated in some pituitary adenomas, however, we have shown that sIL6R is not shed by the majority (92%) of human pituitary adenomas in culture nor by HP75 cells(super)1(/super). The aim of this current study is to determine expression of IL6R by HP75 and if shedding of the soluble form can be induced; phorbol esters and dexamethasone are known agents that can induce shedding of sIL6R.

We have identified expression of the mIL6R in the HP75 cell line using three specific IL6R antibodies by flow cytometry. Using commercially available ELISA kits we measured the levels of sIL6R present into culture supernatant. Unstimulated HP75 cells shed no detectable levels of the receptor into culture medium (sensitivity range 31.25 picograms per ml - 1000 picograms per ml. Neither phorbol-12-13-dibutyrate (PDBu) 10(super)-7(/super)M nor dexamethasone (10nM, 100nM) induced cleavage of the sIL6R from the HP75 cells at 24 and 72 hours. IL6 has no effect on growth in the cell line on incubation after 72 hours but shows a delayed inhibitory effect after 6days. This implies that the IL6R is functional but the delayed response may indicate that it is impaired. The mechanism of action of proteolytic cleavage of the membrane receptor by phorbol esters is not clear, however, the inability of PDBu and dexamethasone to cleave the IL6R has not previously to our knowledge been reported. These data provide evidence that there may be a defect in the IL6R in the shedding process.

(super)1(/super) Kerry, KE Endocrine Abstracts 2001 (bold)1(/bold) P138