A third polypeptide associated with heavy and light chain subunits of class I HLA antigens in immune interferon-treated human melanoma cells

Recombinant immune interferon (IFN-γ) increases the synthesis, expression and shedding of class I HLA antigens by the cultured human melanoma cell line Colo 38. The magnitude of the IFN-γ-induced changes in class I HLA antigens is dependent on both the dose and the time of exposure to IFN-γ and is more pronounced on the heavy chain subunit than on β₂-microglobulin (β₂m). In addition, a third, distinct polypeptide with a molecular mass of 14 kDa is present as a major component of the class I HLA molecular pool in IFN-γ-treated melanoma cells. As IFN-γ preferentially increases the synthesis of the heavy chain over that of β₂m, the newly induced 14-kDa component appears to quantitatively replace β₂m. The stoichiometric relationship between the three molecules suggests that the IFN-γ-induced 14-kDa component may be involved in the insertion of the heavy chain subunit into the plasma membrane.