The human testis-enriched HSPA2 interacts with HIF-1α in epidermal keratinocytes, yet HIF-1α stability and HIF-1-dependent gene expression rely on the HSPA (HSP70) activity.

The Hypoxia-Inducible Factor 1 (HIF-1) is essential for cellular adaptation to reduced oxygen levels. It also facilitates the maintenance and re-establishment of skin homeostasis. Among others, it is involved in regulating keratinocyte differentiation. The stability of the oxygen-liable HIF-1α subunit is regulated by various non-canonical oxygen-independent mechanisms, which among others involve Heat Shock Proteins of the A family (HSPA/HSP70). This group of highly homologous chaperones and proteostasis-controlling factors includes HSPA2, a unique member crucial for spermatogenesis and implicated in the regulation of keratinocyte differentiation. HIF-1 can control the HSPA2 gene expression. In this study, we revealed that HIF-1α is the first confirmed client of HSPA2 in human somatic cells. It colocalises and interacts directly with HSPA2 in the epidermis in situ and immortalised keratinocytes in vitro. Using an in vitro model based on HSPA2-overexpressing and HSPA2-deficient variants of immortalised keratinocytes we showed that changes in HSPA2 levels do not affect the levels and intracellular localisation of HIF-1α or influence the ability of HIF-1 to modulate target gene expression. However, HIF-1α stability in keratinocytes appears critically reliant on HSPAs as a group of functionally overlapping chaperones. In addition to HSPA2, HIF-1α colocalises and forms complexes with HSPA8 and HSPA1, representing housekeeping and stress-inducible HSPA family paralogs, respectively. Chemical inhibition of HSPA activity, but not paralog-specific knockdown of HSPA8 or HSPA1 expression reduced HIF-1α levels and HIF-1-dependent gene expression. These observations suggest that pharmacological targeting of HSPAs could prevent excessive HIF-1 signalling in pathological skin conditions.

P2X7 receptor in normal and cancer cells in the perspective of nucleotide signaling.

Nucleotides are the most common compounds produced constantly by living organisms. They are involved in most cellular processes like the synthesis of other nucleotides and nucleic acids, generation of energy needed for the maintenance of cells, and molecular signaling. In the 70s sir. Geoffrey Burstock discovered a new class of transmembrane proteins - nucleotide receptors responding to nucleotides and their derivatives. For historical reasons, we distinguish two main classes of nucleotide receptors: P1 - which are G protein-coupled adenosine receptors, and P2 - nucleotide receptors that respond to ATP and its derivatives. Additionally, the P2 receptors family can be divided into two subgroups: P2Y - G protein-coupled receptors and P2X cation channel receptors. This paper focuses mainly on the most researched receptor in the nucleotide receptors family - the P2X7 receptor - presenting it in the background of the nucleotide signaling landscape. Almost thirty years of extensive studies on the receptor contributed to understanding protein structure, splicing variants, and mechanism of action in somatic cells. Despite such a wide spectrum of research, the role of the receptor in cancer progression is still undetermined. In many reports, we can find information about the anti-tumorigenic role of this receptor caused by activation of the cell death mechanism after membrane pore formation. These results, however, contradict other studies in which the same receptor is known to promote cancer development through stimulation of proliferation and activation of pro-survival pathways. Ultimately, all this gathered knowledge points to two faces of the receptor in tumor progression. Therefore, we do provide a comprehensive overview of the topic. Finally, we also try to systemize previous and recent literature about the role of this receptor in somatic and cancer cells and provide access to it in the form of a convenient table.

P2X7 receptor: the regulator of glioma tumor development and survival.

P2X7 is an ionotropic nucleotide receptor, forming the cation channel upon ATP stimulation. It can also function as a large membrane pore as well as transmit ATP-dependent signal without forming a channel at all. P2X7 activity in somatic cells is well-known, but remains poorly studied in glioma tumors. The current paper presents the comprehensive study of P2X7 activity in C6 and glioma cell line showing the wide range of effects the receptor has on glioma biology. We observed that P2X7 stimulation boosts glioma cell proliferation and increases cell viability. P2X7 activation promoted cell adhesion, mitochondria depolarization, and reactive oxygen species overproduction in C6 cells. P2X7 receptor also influenced glioma tumor growth in vivo via activation of pro-survival signaling pathways and ATP release. Treatment with Brilliant Blue G, a selective P2X7 antagonist, effectively inhibited glioma tumor development; decreased the expression of negative prognostic cancer markers pro-survival and epithelial-mesenchymal transition (EMT)-related proteins; and modulated the immune response toward glioma tumor in vivo. Finally, pathway-specific enrichment analysis of the microarray data from human patients also showed an upregulation of P2X7 receptor in gliomas from grades I to III. The presented results shed more light on the role of P2X7 receptor in the biology of this disease.

P2X7 receptor activity landscape in rat and human glioma cell lines.

P2X7 is a commonly expressed purinergic receptor, which functions as a cation-permeable channel in the plasma membrane. In certain circumstances, the receptor may also form a large transmembrane pore what results in cell death. P2X7 receptors control numerous physiological and pathological cellular processes and their overexpression is often associated with cancer progression. As nucleotides are important signaling molecules in the central nervous system, P2X7 plays also an important but ambiguous role in glioma biology with contrary observations originating from different glioma models. Therefore, the aim of our research was to investigate P2X7 receptor expression and functions in three human (U-87 MG, U-138 MG, U-251 MG) and one rat (C6) glioma cell lines. Although the receptor mRNA and protein were present in all the studied cells, we found profound differences in their level. We also encountered a problem with one human cell lines authenticity (U-87 MG) and excluded it from most of the experiments. Interestingly, there was no clear dependency between P2X7 receptor level, calcium signal and pore formation ability in the studied glioma lines. In U-138 human cell line, the receptor seemed to be inactive, while in U-251 human and C6 rat cell line its activation resulted in calcium influx and large pore formation. However, the viability of studied cells upon the administration of specific P2X7 agonist - BzATP - was not affected for U-138 and U-251, whereas for C6 cells a stimulatory effect was observed. Our results stress the variability of P2X7 signaling in glioma models and the need for future research which would take into account the complicated landscape of the receptor signaling in the brain.