The flashlights on a distinct role of protein kinase C delta: Phosphorylation of regulatory and catalytic domain upon oxidative stress in glioma cells

Glioblastoma multiforme are considered to be aggressive high-grade tumors with poor prognosis for patient survival. Photodynamic therapy is one of the adjuvant therapies which has been used for glioblastoma multiforme during last decade. Hypericin, a photosensitizer, can be employed in this treatment. We have studied the effect of hypericin on PKCS phosphorylation in U87 MG cells before and after light application. Hypericin increased PKCS phosphorylation at tyrosine 155 in the regulatory domain and serine 645 in the catalytic domain. However, use of the light resulted in apoptosis, decreased phosphorylation of tyrosine 155 and enhanced serine 645. The PKCS localization and phosphorylation of regulatory and catalytic domains were shown to play a distinct role in the anti-apoptotic response of glioma cells. We hypothesized that PKCS phosphorylated at the regulatory domain is primarily present in the cytoplasm and in mitochondria before irradiation, and it may participate in Bcl-2 phosphorylation. After hypericin and light application, PKCS phosphorylated at a regulatory domain which is in the nucleus. In contrast, PKCS phosphorylated at the catalytic domain may be mostly active in the nucleus before irradiation, but active in the cytoplasm after the irradiation. In summary, light-induced oxidative stress significantly regulates PKCS pro-survival and pro-apoptotic activity in glioma cells by its phosphorylation at serine 645 and tyrosine 155. (C) 2017 Elsevier Inc. All rights reserved.