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Cancer is a histologically and genetically heterogeneous population of tumor cells that exhibits distinct molecular profiles determined by epigenetic alterations. P-element-induced wimpy testis (PIWI) proteins in complex with PIWI-interacting RNA (piRNA) have been previously demonstrated to be involved in epigenetic regulation in germline cells. Recently, reactivation of PIWI expression, primarily PIWI-like protein 1 and 2, through aberrant DNA methylation resulting in genomic silencing has been identified in various types of tumors. It has been suggested that the PIWI-piRNA complex contributes to cancer development and progression by promoting a stem-like state of cancer cells, or cancer stem cells (CSCs). It has been identified that CSCs represent the cells that have undergone epithelial-mesenchymal transition (EMT) and acquired metastatic capacities. However, the molecular association between the EMT process and the stem-cell state remains unclear. Further extensive characterization of CSCs in individual types of tumors is required to identify specific markers for the heterogeneous population of CSCs and therefore selectively target CSCs. Previous studies indicate a reciprocal regulation between PIWI proteins and a complex signaling network linking markers characterized for CSCs and transcription factors involved in EMT. In the present review, studies of PIWI function are summarized, and the potential involvement of PIWI proteins in cancer development and progression is discussed.

Background/aim P-Element-induced wimpy testis (PIWI) proteins in complex with PIWI-interacting RNA (piRNA) are involved in epigenetic regulation of gene expression in germline cells. Aberrant expression of piRNA and PIWI proteins have been identified in various types of tumour cells. The aim of this study was to evaluate the expression profiles of PIWI-like protein-1, -2 (PIWIL1 and PIWIL2), their immunohistochemical (IHC) characteristics in ductal breast cancer, and determine their correlation with clinicopathological parameters of this type of cancer. Materials and methods Material for IHC studies comprised of 101 invasive ductal carcinoma (IDC) cases and 31 mastopathy tissues. Frozen fragments of paired tissue specimens (tumour and adjacent non-malignant breast tissue) taken from 55 patients with IDC and 18 samples of mastopathy were used for molecular studies using real-time polymerase chain reaction (RT-PCR). Results A statistically significantly higher level of PIWIL1 and PIWIL2 was found in IDC compared to mastopathy samples (p≤0.0001). Increased expression of PIWIL1 was correlated with increased PIWIL2 expression in breast cancer tissue. Surprisingly, PIWIL1 mRNA was detected only in cancer and mastopathy, but was not found in most normal breast tissues, although it is noteworthy that the PIWIL2 mRNA level was statistically significantly lower in mastopathy and IDC samples compared to normal breast tissues. Conclusion Our results affirm the hypothesis that reactivation of PIWI expression in various caner types is crucial for cancer development.

International audience; In recent years, special attention has been paid to finding new pro-angiogenic factors which could be used in gene therapy of vascular diseases such as critical limb ischaemia (CLI). Angiogenesis, the formation of new blood vessels, is a complex process dependent on different cytokines, matrix proteins, growth factors and other pro- or anti-angiogenic stimuli. Numerous lines of evidence suggest that key mediators of angiogenesis, vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) together with fibroblast growth factor2 (FGF2) are involved in regulation of the normal and pathological process of angiogenesis. However, less information is available on the complex interactions between these and other angiogenic factors. The aim of this study was to characterise the effect of fibroblast growth factor2 on biological properties of human endothelial progenitor cells with respect to the expression level of other regulatory cytokines. Ectopic expression of FGF2 in EP cells stimulates their pro-angiogenic behaviour, leading to increased proliferation, migration and tube formation abilities. Moreover, we show that the expression profile of VEGF and other pro-angiogenic cytokines, such as HGF, MCP2, and interleukins, is affected differently by FGF2 in EPC. In conclusion, we provide evidence that FGF2 directly affects not only the biological properties of EP cells but also the expression pattern and secretion of numerous chemocytokines. Our results suggest that FGF2 could be applied in therapeutic approaches for CLI and other ischaemic diseases of the vascular system in vivo.

Four human colon adenocarcinoma cell line variants with different metastatic potential were used to examine whether a correlation exists between actin level, state of actin polymerization and invasiveness of tumour cells. Monomeric (G), total (T) and filamentous (F) actin were determined in the cytosolic fraction of these cells. A statistically significant decrease in G actin level and increase in the state of actin polymerization (measured by F:G actin ratio) were found in the cytosol of three cell variants with higher metastatic potential and invasiveness (EB3, 3LNLN, 5W) compared with the parental cell line (LS180). Our experimental data lead to the conclusion that there is a correlation between the metastatic capacity of human colon adenocarcinoma cells and the state of actin polymerization.