Genetics--cellular basis

Protocadherin 20 promotes ferroptosis by suppressing the expression of Sirtuin 1 and promoting the acetylation of nuclear factor erythroid 2-related factor 2 in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is characterized by a poor prognosis. Our previous work suggested that Protocadherin 20 (PCDH20) promoted ferroptosis in HCC. Nevertheless, the underlying mechanism remains elusive. Recently, we found that both the mRNA and protein levels of PCDH20 were upregulated in erastin- or sorafenib-treated HCC cells. Meanwhile, data showed that Sirtuin 1 (SIRT1) was markedly downregulated in PCDH20-SNU-449 cells. Additionally, overexpression of PCDH20 or erastin-treated cells dramatically decreased cell viability and colony-forming capacity of HCC cells, whereas blocking PCDH20 reversed these effects. Moreover, PCDH20 overexpression or treatment with erastin significantly downregulated the expression of SIRT1, Solute carrier family 7 member 11 (SLC7A11), as well as the ferroptosis-related protein glutathione peroxidase 4 (GPX4) and glutathione (GSH), while elevated malondialdehyde (MDA), 2'- 7'-dichlorofluorescein (DCF) and intercellular iron levels. Conversely, knockdown of PCDH20 upregulated SIRT1 and SLC7A11. Immunoprecipitation assay demonstrated that PCDH20 or erastin increased the amount of acetylated nuclear factor erythroid 2-related factor-2 (NRF2). This reducing effect of NRF2 deacetylation by PCDH20 was counteracted by restoring the expression of SIRT1. In addition, PCDH20 lowered the levels of GPX4, GSH, and cell viability, as well as resulted in an elevation in intercellular iron level, MDA, and DCF. These effects were reversed by SIRT1 expression. Besides, PCDH20 could promote ferroptosis by inhibiting SIRT1 from deacetylating NRF2, which led to the downregulation of SLC7A11, GPX4, and GSH both in vivo and in vitro. Our results signals that PCDH20 promotes ferroptosis by suppressing the expression of SIRT1 and thus, promoting the acetylation of NRF2in HCC.

Htid-1, the human homolog of the Drosophila melanogaster l(2)tid tumor suppressor, defines a novel physiological role of APC

Htid-1, the human counterpart of the Drosophila tumor suppressor gene lethal(2)tumorous imaginal discs (l(2)tid) encodes three splice forms translated into three cytosolic - Tid50, Tid48 and Tid46 - and three mitochondrial - Tid43, Tid40 and Tid38 - proteins. Here we provide evidence for the association of the endogenous Tid50/Tid48 proteins with the adenomatous polyposis coli (APC) tumor suppressor in normal colon epithelium, colorectal cancer cells and mouse NIH3T3 fibroblasts. Using the Glutathione S-transferase binding assay we show that the N-terminal region including the Armadillo domain (ARM) of APC is sufficient to bind the Tid molecules. Using immunoprecipitation and confocal microscopy we show that the two molecular partners complex at defined areas of the cells with further proteins such as Hsp70, Hsc70, Actin, Dvl and Axin. Our data implicate that the formation of the complex is not associated with APC's involvement in beta-Catenin degradation. Furthermore, though it is linked to Actin it is neither associated with regulation of Actin cytoskeleton due to APC's binding to Asef nor to Tid's binding to Ras-GAP. We suggest that the novel complex acts in maintaining APC's availability for its distinct roles in the Wnt signaling important for the cell to take the right decision, either to switch the cascade OFF or ON, thus, to regulate the onset of proliferation of the cells.

Leukomogenic factors downregulate heparanase expression in acute myeloid leukemia cells

Heparanase is a heparan sulfate-degrading endoglycosidase expressed by mature monocytes and myeloid cells, but not by immature hematopoietic progenitors. Heparanase gene expression is upregulated during differentiation of immature myeloid cells. PML-RARalpha and PLZF-RARalpha fusion gene products associated with acute promyelocytic leukemia abrogate myeloid differentiation and heparanase expression. AML-Eto, a translocation product associated with AML FAB M2, also downregulates heparanase gene expression. The common mechanism that underlines the activity of these three fusion gene products involves the recruitment of histone deacetylase complexes to specific locations within the DNA. We found that retinoic acid that dissociates PML-RARalpha from the DNA, and which is used to treat acute promyelocytic leukemia patients, restores heparanase expression to normal levels in an acute promyelocytic leukemia cell line. The retinoic acid effects were also observed in primary acute promyelocytic leukemia cells and in a retinoic acid-treated acute promyelocytic leukemia patient. Histone deacetylase inhibitor reverses the downregulation of heparanase expression induced by the AML-Eto fusion gene product in M2 type AML. In summary, we have characterized a link between leukomogenic factors and the downregulation of heparanase in myeloid leukemic cells.

Cytoskeletal network in colon cancer: from genes to clinical application

Colorectal cancer arises from well-defined sequential steps characterised by distinct genetic events. Abnormalities in the expression and functional activity of cell adhesion molecules are implicated in the development and progression of the majority of colorectal cancers. Intercellular (e.g. E-cadherin/catenin complex) and cell-matrix (e.g. integrins) adhesion molecules are more than just cementing substances but regulate cell polarity, differentiation, proliferation, migration and invasion. Many of these cellular events are mediated through their intimate association with the actin cytoskeletal network. A dynamic actin cytoskeleton characterises normal epithelial cells and polymerisation and depolymerisation of actin filaments enables cell shape to change during migration and mitosis. In colorectal cancer, cells lose actin cytoskeletal organisation and normal cell adhesion when they become invasive. Future investigations should allow the unravelling of new cytoskeletal network functions in tumour biology and may lead to the development of novel therapeutic strategies based on the manipulation of its associated molecules.