HEMATOPOIETIC STEM-CELL INHIBITOR (SCI MIP-1-ALPHA) ALSO INHIBITS CLONOGENIC EPIDERMAL KERATINOCYTE PROLIFERATION

The maintenance and regulation of continuously renewing tissues is ult imately controlled at the level of stem-cell proliferation. We have re cently identified a reversible inhibitor of hemopoietic stem-cell prol iferation (stem-cell inhibitor [SCI]), which is identical to the macro phage inflammatory protein, MIP-1alpha, a 69-amino-acid heparin-bindin g cytokine. To test the cell/tissue specificity of the inhibition of p roliferation by SCI/MIP-1alpha, we have investigated its activity on e pidermal keratinocytes, the principal cell type of another continuousl y renewing tissue. Here we show that SCI/MIP-1alpha inhibits the proli feration of epidermal keratinocytes in vitro and that the MIP-1alpha m RNA is present in epidermal Langerhans cells but not in keratinocytes. This suggests an important growth regulatory function for SCI/MIP-1al pha in keratopoiesis, as well as hemopoiesis, and may also indicate a novel role for the epidermal Langerhans cell. As SCI/MIP-1alpha can in hibit the proliferation of embryologically distinct precursor cells, t his raises the possibility that it may also function in a number of ot her tissues.