In animals with implanted glial brain tumors, intravenously injected HSCs migrate to the tumor nidus and accumulate in areas of invasion and necrosis (32). and a lower level of TGF-1 synthesis. Therefore, this transformation may initiate cell migration from hypoxic areas to other areas with a better blood supply, where the local microenvironment may be more favorable. This hypothesis is supported by the gradual decrease in replicative activity among cancer cells in the present study, when the TGF-1 concentration was reduced to 20 and 10 ng/ml. Other studies also support this hypothesis (18,19). On the one hand, this mechanism hinders the progress of the neoplastic process; on the other hand, it ensures the selection of L-779450 hypoxia-resistant cellular elements that make a tumor more aggressive. Switching from a proliferation to a migration program is reflected by more active interaction with the surface of the culture plate. TGF-1 stimulation leads to an intensification of exocrine function in cancer cells, causing a decrease in the number of intracellular inclusions and intercellular contacts, and creating multiple exocyte bubbles and actively releasing cell contents (22). The synthesis of extracellular matrix components combined with the production of proteolytic enzymes is an important part of a complex invasive growth program (23). By secreting components of the extracellular matrix and interacting with them, a cancer cell may penetrate the surrounding tissues. The ability of cancer cells to synthesize components of the extracellular matrix may be considered to be a crucial mechanism in shaping the aggressive nature of cancer (24). The production of matrix proteins and molecules involved with cellular adhesion and migration explains the marked alteration in the shape of cells and the appearance of multiple filopodia (25). However, the present study suggested that these changes do not exclude a possibility of coordinated interaction among glioblastoma cells due to a complex system of intercellular communication creating a unified system of cells. Cross-talk between cells in living organisms is based on the exchange of information. With the help of intercellular interactions, the coordinated regulation of metabolism, differentiation and cell proliferation occurs in different tissues. The complex system of microtubes joining glioblastoma cells merits consideration. Certain studies have suggested that there is a cancer cell communication network (24C27). This network is thought to be responsible for transporting proteins that confer chemoresistance and radiation resistance, proteins responsible for DNA repair, microRNAs (miRNAs) disrupting the processes of epigenetic control over oncogene expression, the hierarchical development of glioblastoma cells (6), and the creation of CSC niches (21). It is known that the development of an invasive phenotype in cancer cells following stimulation by TGF-1, as described by TRADD the authors of the present study (20) and others (23), is not limited by their localization. Appearing as a response to the local conditions, a transformed resistant and invasive molecular phenotype is transmitted to other cells through adhesive contacts, multiple connective tubes, the fusion of cancer cells and the production of microvesicles. To an extent, this L-779450 system of communication may explain the dynamic nature of CSC populations, and the presence of cancer/stem progenitor cells, tumor-inducing cells and other neoplastic elements with properties that are not typical for ordinary glioblastoma cells (6,13,14). The production of microvesicles is one of the less-studied types of communication between neoplastic cancer cells (24C26). This type of communication is used for long-distance transportation of materials or to protect materials from an aggressive microenvironment. In addition to DNA and RNA, microvesicles may transport CD44, CD133+ mitogen activated protein kinase, epidermal growth factor vIII receptor, disintegrin and metalloproteinase domain-containing protein 10, Annexin A2 and certain pro-metastatic molecules (28C30). It is possible to transfer drug resistance between invasive glioma cells through exosomes (31). Therefore, it is possible make a justified assumption that microvesicle synthesis is a self-sufficient mechanism of tumor aggression, which renders it possible to transfer an invasive phenotype to other cells and tissues. Normal CD45+ CD34+ HSCs are able to migrate to cells of different types, although they have increased mobility towards cancer cells. In animals with implanted glial brain tumors, intravenously injected HSCs migrate to the tumor nidus and accumulate in areas of invasion and necrosis (32). A previous study reported that hematopoietic CD34+ CD45+ stem cells migrate towards glioblastoma cells and interact with them, indicative of a strong association between these cell types (32). It is possible that by recruiting bone marrow cells, the tumor creates its own microenvironment, allowing it to optimize resources and escape the innate immune system and L-779450 other defense mechanisms of the body (32)..