Investigation of P38 and AKT Inhibitor Effects on SPARC and PTEN-Induced Signaling in Glioma Cells
Romph, Camryn R.
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Glioblastoma (GBM), the most malignant type of adult brain cancer, affects thousands of patients annually in the U.S. Though these tumors rarely metastasize, GBM is characterized by its invasive phenotype, limiting survival to less than two years postdiagnosis. While a myriad of signaling pathways regulate GBM, SPARC, an extracellular matrix protein, is of particular interest due to its overexpression in GBM. Downstream proteins of SPARC, such as AKT, P38, MK2, and HSP27, correlate with survival and migration of glioma cells and are tested in the present study. PTEN, a tumor suppressor generally lost in GBM patients, inhibits signaling through the SPARC-induced pathways. Four established U87 malignant glioma (MG) clones and three non-cancerous cell lines were used, all of which differ in SPARC and PTEN status. Cell lines were tested in eight treatment conditions: an AKT inhibitor, three P38 inhibitors, and combinations of the AKT inhibitor with each P38 inhibitor. Changes in levels of pAKT, pHSP27, pP38, and pMK2 were detected by Western blot analysis. Results for HSP27 show that in SPARC-/ PTEN- cells, Ser82 pHSP27 is reduced with P38 and AKT inhibition together. In SPARC-/ PTEN+ cells, inhibitors do not affect pHSP27 expression at any site, which supports that PTEN may indirectly suppress pHSP27. In SPARC+/ PTEN- cells, Ser82 pHSP27 is reduced by P38 inhibition alone and combination treatment. SPARC+/PTEN+ cells showed that all inhibitor treatments shut down SPARC-induced Ser78 pHSP27 expression. Results provide mechanistic implications for signaling downstream of SPARC. Future studies should compare cell lines on the same blot so quantifiable amounts may be compared, and treatments should be tested in survival and migration assays to determine which condition best prevents the invasive phenotype of GBM.