Different response of breast cancer cell lines to PMA treatment

B11 Breast cancer is the most common malignancy and accounts for 33% of all incident cancers in women in North America. Approximately one-third of women with breast cancer develop metastases and ultimately die from the disease. The current and future cancer treatment is mostly based on research on breast cancer cell lines so that their detailed molecular analysis may yield a better diagnostic test. There are several kinds of cell lines representing breast cancer. These cell lines have some common characteristics showing their breast cancer origin, like expressing milk proteins, but the cell lines show some discrepancies as well.
 Integrins are a large family of heterodimeric proteins that mediate cell-cell and cell-extra cellular matrix adhesion. αvβ3 is one of the integrins that is not expressed in high levels in normal tissues but in some cancer cells its higher expression is correlated directly to tumorogenecity. Although the expression of αvβ3 integrin and other related proteins have been studied in different cell lines, but there is not enough information on the effect/s of PMA on the expression of αvβ3 and different signaling proteins in breast cancer cell lines.
 In this paper three different kinds of breast cancer cell (BCC) lines; MDA-435, MDA-231, and MCF7 were treated with PMA. Beside these cell lines a non-breast cancer cell line (Hek-293) was studied along other cell lines for any possible differences. The time course PMA-treatment included, 30m, 1h, 2h, 4h and 6h. Western blot analysis and flow cytometry techniques were used to compare the level of αv, β3, αvβ3, Erk, phospho Erk, Src, phospho Src, Fak and phospho Fak proteins in these cells before and after PMA treatment.
 Flow cytometry and Western blot analysis revealed that all the cell lines express αv subunit, but only MDA-435 expressed αvβ3 integrin. PMA treatment increases αv level in MDA-435, while in other cell lines don’t change significantly. Western blot analysis demonstrated that MDA-231 expressed the highest level of FAK, which increases after a 1-2 hour exposure to PMA. The highest level of c-Src protein was detected in MDA-435 cells and the lowest in MCF7. PMA treatment increases c-Src level in MDA-435, and decreases in Hek-293. All the cell lines expressed detectable levels of Erk1/2, the level of which, did not change with PMA treatment. No phospho Erk was detected in untreated cells while PMA treatment resulted in a differential pattern of phospho Erk expression. PMA treatment induced Erk phosphorylation in MDA-435 and MCF7 after a 30 to 120 minutes, a gradual increase over six hours in MDA-231 cells, and at all times in Hek-293s.All the cell lines show the same level of Mek1/2 before or after PMA treatment, but only MDA-435 and MDA-231 show activation of phospho-Mek before PMA treatment. PMA treatment, resulted in phospho-Mek activation in MDA435 and Hek-293 after 30m to 4 h, after 30m to 2h in MDA-231, and barely detectable levels were detected in MCF7. Our results show that different cancer cell lines respond differently to PMA. These differences are more prominent in MAPK pathway (phospho Erk and phospho Mek). As MAP kinase pathway is one of the potential biomarker in cancer prevention, these findings may have applications in genetic epidemiology and prevention of breast cancer.

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