Endocrine Abstracts

The N-terminal fragment of human POMC consists of a 76 residue peptide (also known as pro-gamma-MSH) that contains the sequence of gamma-MSH in its C-terminus. Previous studies have demonstrated that the N-terminal portion not containing the gamma-MSH sequence is a potent adrenal mitogen while gamma-MSH itself can act synergistically with ACTH to increase steroid output.

Since previous studies [1] have suggested that N-POMC 1-28 can stimulate the ERK pathway in human H295R adrenal cells we investigated ERK activation in the mouse adrenocortical Y1 cell line.

Y1 cells obtained from the ECACC (a clone not expressing the ACTH receptor) were grown to confluence in 90 mm dishes before being serum starved for 48hrs. The cells were then stimulated for various times with either 1nM Lys-gamma3-MSH, N-POMC 1-49 or pro-gamma-MSH (purified from bovine pituitaries) or synthetic N-POMC 1-28. The cells were lysed and subsequently analysed for ERK activation using immunoblotting.

We found that all peptides stimulated ERK phosphorylation. Both N-POMC 1-28 and 1-49 stimulated a maximal response within 5mins returning to basal within 20mins whilst gamma-MSH resulted in a slower activation, with a maximal at 15 mins and returning to basal after 30 mins. In contrast, pro-gamma-MSH induced a small ERK phosphorylation after 5 mins returning to basal by 10 mins. Immunoblotting with a phospho MEK antibody showed a similar pattern of phosphorylation.

These results support the earlier results in the H295R cell line that N-POMC peptides can activate the ERK pathway. The fact that the kinetics of this activation are not identical for the different peptides suggests that the upstream regulators of MEK eg the RAF family, may not be identical for N-POMC 1-28/49 and gamma-MSH.

[1] Fasnnacht et al 2003 JCEM 88: 2171-2179.