Date of Award
Doctor of Philosophy (PhD)
Charles D Rice
Lesly A Temesvari
Breast cancer is the most common diagnosed and deathly cancer in women all over the world. Besides the conventional cancer therapy, based on the receptors expressed in breast cancer, hormone therapy targeting estrogen receptors (ER) and progesterone receptors (PR), and targeted therapy using antibodies or inhibitors targeting human epidermal growth factor receptor 2 (HER2) are the common and standard treatments for breast cancer. However, breast cancer is a highly heterogeneous disease. About 15-20% of breast cancers do not significantly express the three receptors, which are classified as the triple-negative breast cancer and the most dangerous type of breast cancer because of lack of effective targets for treatment. New and more targets in breast cancer are an urgent need in breast cancer treatment. The plasma human prolactin (PRL) was reported positively associated with the risk of breast cancer, and breast cancer cells can synthesize PRL locally as an autocrine/paracrine growth factor; the prolactin receptor (PRLR) was found overexpressed in 80% of human breast cancer cells and tissues, implicating that PRL/PRLR pathway could be a potential target for breast cancer treatment.
We created a bifunctional fusion protein MICA-G129R to target the PRLR on breast cancer cells. The G129R is an antagonistic variant of PRL, which binds to PRLR and induces apoptosis of the target cells instead of promotes their growth. MICA (MHC class I chain-related protein) is a stress-induced protein and ligand of the activating receptor NKG2D of natural killer (NK) cells. Advanced cancer cells tend to down-regulate or shed stress signal proteins, like MICA, to evade immune surveillance and elimination. We hypothesize that the MICA-G129R fusion protein could bridge the NK cells and PRLR-positive breast cancer cells, activate NK cells through the MICA portion and target PRLR-positive breast cancer cells through the G129R portion.
We expressed the MICA-G129R fusion protein and demonstrated that it bound to human natural killer NK-92 cells and human PRLR-positive breast cancer T-47D cells, and significantly enhanced the cytotoxicity of NK-92 cells to kill T-47D cells at different effector/target ratios. The enhancement was only observed by using MICA-G129R fusion protein but not the MICA only or the G129R only proteins. We compared the T-47D cell with PRLR-negative HeLa cells and found that HeLa cells were killed more in the co-culture with NK-92 cells mediated by MICA-G129R fusion protein. When ectopically expressing PRLR in HEK293 cells, these originally PRLR-negative cells became sensitive to the cytotoxicity mediated by MICA-G129R and were lysed. The results indicate that the MICA-G129R fusion protein mediated cytotoxicity targets PRLR-positive cells. We also demonstrated that the MICA-G129R protein activated NK cells to release the cytotoxic molecule granzyme B and cytokine IFN-γ which play key roles in cytotoxicity, and the cytotoxicity mediated by the MICA-G129R fusion protein triggered apoptosis in target cells.
In conclusion, the bifunctional fusion protein MICA-G129R bridges NK cells and PRLR-positive breast cancer cells and enhances the cytotoxicity targeting a new receptor in breast cancer.
Ding, Hui, "MICA-G129R: A Bifunctional Fusion Protein Bridging Natural Killer Cells and PRLR-positive Breast Cancer Cells" (2020). All Dissertations. 2690.