Journal of Carcinogenesis & Mutagenesis

Abstract

Intermediate Filament Proteins of Lamin A/C and Cytokeratin 18 are involved in Apoptotic Induction by Photodynamic Therapy with Hexaminolevulinate in Human Colon Carcinoma Cells

Susan Shahzidi, Mouldy Sioud, Andreas Brech, Sebastian Patzke, Jahn M. Nesland and Qian Peng

Hexaminolevulinate (HAL), a hexylester of 5-aminolevulinic acid, is a precursor of the photosensitizer protoporphyrin IX (PpIX) and clinically used for photodynamic therapy (PDT) of cancer, an established modality with a light-activated drug. However, the mechanism involved in the killing cancer cells is still not fully understood. Our previous report (Cancer Lett., 2013; 339: 25-32) has shown a crucial role of caspase-6-mediated cleavage of lamin A/C, a member of type-V intermediate filaments (IFs), in the HAL-PDT-induced apoptosis in human B-cell lymphoma cells. Lamin A/C is present in all cell types; while cytokeratin 18, a major component of type-I IFs, is expressed only in the epithelial cells and carcinoma. This study has focused upon the roles of the two IF proteins, lamin A/C and cytokeratin 18 in the HAL-PDT-mediated apoptotic induction in the human colon carcinoma COLO 205 and HCC2998 cell lines. HAL-PDT-induce apoptosis was confirmed by fluorescence microscopy, electron microscopy and M30 CytoDeath™ ELISA in both cell lines. Fluorescence microscopy, immunoblots and immunocytochemistry showed that both lamin A/C and cytokeratin 18 were involved in the apoptotic induction and the specific caspase-6 inhibitor stopped not only the cleavages of the two IF proteins, but also the apoptotic induction. Knockdown of both lamin A/C and cytokeratin 18 by siRNAs induced the cells to be apoptotic, further supporting the hypothesis that the disruption of both lamin A/C and cytokeratin 18 is required in the apoptotic induction by HAL-PDT in the human carcinoma cells.