Discipline: Biological Sciences
Subcategory: Cancer Research
Angel Garcia - Tougaloo College
Co-Author(s): Marcelo Jun Sakiyama and Christian Gomez, University of Mississippi Medical Center, Jackson, MS
sMICA is cleaved from the cell membrane and plays a critical role in cell response to stress. High levels of sMICA have been found in several types of cancer and may play a crucial role in immunoevasion by downregulating receptors on NK cells and T cells. We hypothesized that sMICA expression would be expressed in commonly used Prostate Cancer (PCa) cell lines and its expression would be higher under stress conditions, such as those found in tumor microenvironment. LNCaP cells were cultured under different levels of oxygen [20%O2 (normoxia) or 2%O2 (hypoxia)]. Cells were incubated for 24 hours and 48 hours. sMICA was detected using a commercial ELISA assay (DuoSet R&D Systems). sMICA concentration was also tested in the plasma of healthy donors, PCa patients, and rheumatoid arthritis patients. To measure cellular levels of MICA, cells were grown under hypoxia and normoxia conditions during 0, 24, and 48 hours. Cell lysates were prepared and analyzed for MICA by Western blot technique. After 48 hours, the cells in hypoxia showed approximately 5 times more sMICA than cells in normoxia. In plasma from PCa patients, sMICA was found to be close to 3 times higher than in the pool of healthy donors. Rheumatoid arthritis patients showed about a 33% more expression of sMICA than PCa patients. This last result is consistent with the highly inflammatory nature of rheumatoid arthritis. Western blot analysis in LNCaP cell lysates showed that normal oxygen levels increased MICA by 3.5-fold. Hypoxia reduced MICA expression by 11%. Our findings suggest that sMICA is released to the medium of PCa cells in response to a variation in oxygen levels. The results from the patient plasma imply that the expression of sMICA may be differentially affected by pathological conditions. Future experiments will allow us to examine if MICA can be used as a reliable indicator of the ability of PCa cells to evade the immune system. Evidence of this association would support further studies designed to evaluate the value of sMICA as an immunotherapeutic target in PCa.
Reference: Y. N., Yamanegi K., Ohyama H., Masaki H., Nakasho K., Futani H., Okamura H., Terada N. 2012. Hypoxia Downregulates the Expression of Cell Surface MICA Without Increasing Soluble MICA in Osteosarcoma Cells in a HIF-1αdependent Manner. International Journal of Oncology 41:20012012, 2012.
Funder Acknowledgement(s): This work is supported by the Department of Defense through the University of Mississippi Undergraduate Prostate Cancer Research Program (#W81XWH14-1-0151).
Faculty Advisor: Christian Gomez,