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.