Deleted in liver cancer protein family in human malignancies (Review)

The Deleted in Liver Cancer (DLC) protein family comprises proteins that exert their function mainly by the Rho GTPase-activating protein (GAP) domain and by regulation of the small GTPases. Since Rho GTPases are key factors in cell proliferation, polarity, cytoskeletal remodeling and migration, the aberrant function of their regulators may lead to cell transformation. One subgroup of these proteins is the DLC family. It was found that the first identified gene from this family, DLC1, is often lost in hepatocellular carcinoma and may be involved as a tumor suppressor in the liver. Subsequent studies evaluated the hypothesis that the DLC1 gene acts as a tumor suppressor, not only in liver cancer, but also in other types of cancer. Following DLC1, two other members of the DLC protein family, DLC2 and DLC3, were identified. However, limited published data are available concerning the role of these proteins in malignant transformation. This review focuses on the structure and the role of DLC1 and its relatives in physiological conditions and summarizes data published thus far regarding DLC function in the neoplastic process.

Differential distribution of Ca2+-activated potassium channel beta4 subunit in rat brain: immunolocalization in neuronal mitochondria

Large conductance Ca(2+)-activated potassium channels (BK(Ca) channels) are expressed in the plasma membrane of various cell types. Interestingly, recent studies provided evidence for the existence of BK(Ca) channels also in mitochondria. However, the molecular composition of these channels as well as their cellular and tissue distribution is still unknown. The goal of the present study was to find a candidate for the regulatory component of the mitochondrial large conductance calcium activated potassium (mitoBK(Ca)) channel in neurons. A combined approach of Western blot analysis, high-resolution immunofluorescence and immunoelectron microscopy with the use of antibodies directed against four distinct beta subunits demonstrated the presence of the BK(Ca) channel beta4 subunit (KCNMB4) in the inner membrane of neuronal mitochondria in the rat brain and cultured neurons. Within the cell, the expression of beta4 subunit was restricted to a subpopulation of mitochondria. The analysis of beta4 subunit distribution throughout the brain revealed that the highest expression levels occur in the thalamus and the brainstem. Our results suggest that beta4 subunit is a regulatory component of mitochondrial BK(Ca) channels in neurons. These findings may support the perspectives for the neuroprotective role of mitochondrial BK(Ca) channel in specific brain structures.

Heme oxygenase-1 protects tumor cells against photodynamic therapy-mediated cytotoxicity

Photodynamic therapy is a promising antitumor treatment modality approved for the management of both early and advanced tumors. The mechanisms of its antitumor action include generation of singlet oxygen and reactive oxygen species that directly damage tumor cells and tumor vasculature. A number of mechanisms seem to be involved in the protective responses to PDT that include activation of transcription factors, heat shock proteins, antioxidant enzymes and antiapoptotic pathways. Elucidation of these mechanisms might result in the design of more effective combination strategies to improve the antitumor efficacy of PDT. Using DNA microarray analysis to identify stress-related genes induced by Photofrin-mediated PDT in colon adenocarcinoma C-26 cells, we observed a marked induction of heme oxygenase-1 (HO-1). Induction of HO-1 with hemin or stable transfection of C-26 with a plasmid vector encoding HO-1 increased resistance of tumor cells to PDT-mediated cytotoxicity. On the other hand, zinc (II) protoporphyrin IX, an HO-1 inhibitor, markedly augmented PDT-mediated cytotoxicity towards C-26 and human ovarian carcinoma MDAH2774 cells. Neither bilirubin, biliverdin nor carbon monoxide, direct products of HO-1 catalysed heme degradation, was responsible for cytoprotection. Importantly, desferrioxamine, a potent iron chelator significantly potentiated cytotoxic effects of PDT. Altogether our results indicate that HO-1 is involved in an important protective mechanism against PDT-mediated phototoxicity and administration of HO-1 inhibitors might be an effective way to potentiate antitumor effectiveness of PDT.