Alpha-MSH regulates protein ubiquitination in T cells.

The neuropeptide alpha-melanocyte stimulating hormone (alpha-MSH) suppresses IFN-gamma + T cells from mice. We discovered, however, that despite this significant production by DTH-mediating effector CD4 supression of IFN-gamma production, alpha-MSH-treated effector T cells had the same level of IFN-gamma mRNA expression and intracellular IFN-gamma protein as untreated activated T cells. In order to explain why IFN-gamma production was suppressed in the face of unchanged mRNA and intracellular IFN-gamma levels, we looked for mechanisms that could increase the degradation of IFN-gamma within the alpha-MSH-treated T cells. Among the known pathways of post-translational intracellular protein modification, the ubiquitin-proteosome system was examined in alpha-MSH-treated T cells to see if a post-translational protein modification occurred to prevent IFN-gamma secretion from the cell. Immunoblots from alpha-MSH-treated T cells showed higher levels of protein ubiquitination when compared to untreated T cells. Resting T cells treated with alpha-MSH also demonstrated enhanced protein ubiquitination. We found that IFN-gamma is one of the ubiquitinated proteins in the alpha-MSH-treated activated T cells. Our results demonstrate that one of the mechanisms by which alpha-MSH regulates T cell activity is through mediating a change in the pattern of protein ubiquitination in T cells.