Pharmaceutical Sciences Faculty Publications

Title

Phorbol 12-Myristate 13-Acetate Induces Epidermal Growth Factor Receptor Transactivation via Protein Kinase Cdelta/c-Src Pathways in Glioblastoma Cells

Document Type

Article

Publication Date

3-4-2005

Journal Title

Journal of Biological Chemistry

ISSN

0021-9258

Volume

280

Issue

9

First Page

7729

Last Page

7738

DOI

http://dx.doi.org/10.1074/jbc.m409056200

PubMed ID

15618223

PubMed Central® ID

PMC1351089

Abstract

Both the epidermal growth factor receptor (EGFR) and protein kinase C (PKC) play important roles in glioblastoma invasive growth; however, the interaction between the EGFR and PKC is not well characterized in glioblastomas. Treatment with EGF stimulated global phosphorylation of the EGFR at Tyr845, Tyr992, Tyr1068, and Tyr1045 in glioblastoma cell lines (U-1242 MG and U-87 MG). Interestingly, phorbol 12-myristate 13-acetate (PMA) stimulated phosphorylation of the EGFR only at Tyr1068 in the two glioblastoma cell lines. Phosphorylation of the EGFR at Tyr1068 was not detected in normal human astrocytes treated with the phorbol ester. PMA-induced phosphorylation of the EGFR at Tyr1068 was blocked by bisindolylmaleimide (BIM), a PKC inhibitor, and rottlerin, a PKCδ-specific inhibitor. In contrast, Gö 6976, an inhibitor of classical PKC isozymes, had no effect on PMA-induced EGFR phosphorylation. Furthermore, gene silencing with PKCδ small interfering RNA (siRNA), siRNA against c-Src, and mutant c-Src(S12C/S48A) and treatment with a c-Src inhibitor (4-amino-5-(4-chlorophenyl)-7-(t-butyl) pyrazolo[3,4-d]pyrimidine) abrogated PMA-induced EGFR phosphorylation at Tyr1068. PMA induced serine/threonine phosphorylation of Src, which was blocked by both BIM and rottlerin. Inhibition of the EGFR with AG 1478 did not significantly alter PMA-induced EGFR Tyr1068 phosphorylation, but completely blocked EGF-induced phosphorylation of the EGFR. The effects of PMA on MAPK phosphorylation and glioblastoma cell proliferation were reduced by BIM, rottlerin, the MEK inhibitor U0126, and PKCδ and c-Src siRNAs. Taken together, our data demonstrate that PMA transactivates the EGFR and increases cell proliferation by activating the PKCδ/c-Src pathway in glioblastomas.

Keywords

Epidermal growth, protein kinase, PKC, glioblastoma, cell proliferation