CELL CYCLE-DEPENDENT EXPRESSION OF TAP1, TAP2, AND HLA-B27 MESSENGER-RNAS IN A HUMAN BREAST-CANCER CELL-LINE

Tumor cells are generally poorly responsive to immunotherapy. The resu lts presented here suggest that antigen presentation of somatic tumor cells may be diminished greatly in quiescence and may be determined in part by growth regulation. Peptides produced by proteasomes are trans ported into the endoplasmic reticulum by transporter proteins TAP-1 an d TAP-2, where they bind and stabilize MHC class I molecules required for antigenic presentation on the cell surface, TAP-1 and TAP-2 mRNAs were undetectable in quiescent, serum-deprived human breast cancer cel ls (21PT). They appeared 10 h after serum induction, near the G(1)-S b oundary. In contrast, HLA-B27 mRNA was biphasically up-regulated. Thes e mRNAs were significantly down-regulated in most tissues that contain mainly terminally differentiated, nonproliferating cells. All of the investigated breast cancer cell lines showed lower expression levels o f these mRNAs than did the corresponding normal cells.