RNA–protein interactions are crucial for most biological processes in all organisms. However, it appears that the complexity of RNA-based regulation increases with the complexity of the organism, creating additional regulatory circuits, the scope of which is only now being revealed. It is becoming apparent that previously unappreciated features, such as disordered structural regions in proteins or non-coding regions in DNA leading to higher plasticity and pliability in RNA–protein complexes, are in fact essential for complex, precise and fine-tuned regulation. This review addresses the issue of the role of RNA–protein interactions in generating eukaryotic complexity, focusing on the newly characterized disordered RNA-binding motifs, moonlighting of metabolic enzymes, RNA-binding proteins interactions with different RNA species and their participation in regulatory networks of higher order.

Introduction The majority of breast cancers (BCs) are characterized by the expression of estrogen receptor alpha (ERα+). ERα acts as ligand-dependent transcription factor for genes associated with cell survival, proliferation, and tumor growth. Thus, blocking the estrogen agonist effect on ERα is the main strategy in the treatment of ERα+ BCs. However, despite the development of targeted anti-estrogen therapies for ER+ BC, around 30–50% of early breast cancer patients will relapse. Acquired resistance to endocrine therapy is a great challenge in ER+ BC patient treatment. Discussion Anti-estrogen resistance is a consequence of molecular changes, which allow for tumor growth irrespective of estrogen presence. Those changes may be associated with ERα modifications either at the genetic, regulatory or protein level. Additionally, the activation of alternate growth pathways and/or cell survival mechanisms can lead to estrogen-independence and endocrine resistance. Conclusion This comprehensive review summarizes molecular mechanisms associated with resistance to anti-estrogen therapy, focusing on genetic alterations, stress responses, cell survival mechanisms, and cell reprogramming.

Background: HAX-1 has been described as a protein potentially involved in carcinogenesis and especially metastasis. Its involvement in regulation of apoptosis and cell migration along with some data indicating its overexpression in cancer cell lines and tumors suggests that HAX-1 may play a role in neoplastic transformation. Here we present the first systematic analysis of HAX-1 expression in several solid tumors.Methods: Using quantitative RT-PCR, we have determined the mRNA levels ofHAX1splice variant I in several solid tumors. We have also analyzed by semiquantitative and quantitative RT-PCR the expression of fiveHAX-1splice variants in breast cancer samples and in normal tissue from the same individuals. Quantitative PCR was also employed to analyze the effect of estrogen onHAX1expression in breast cancer cell line. Immunohistochemical analysis of HAX-1 was performed on normal and breast cancer samples.Results: The results reveal statistically importantHAX1up-regulation in breast cancer, lung cancer and melanoma, along with some minor variations in the splicing pattern. HAX-1 up-regulation in breast cancer samples was confirmed by immunohistochemical analysis, which also revealed an intriguing HAX-1 localization in the nuclei of the tumor cells, associated with strong ER status.Conclusion: HAX-1 elevated levels in cancer tissues point to its involvement in neoplastic transformation, especially in breast cancer. The connection between HAX-1 nuclear location and ER status in breast cancer samples remains to be clarified.

HAX‐1 is a multi‐functional protein that is involved in the regulation of apoptosis, cell motility and calcium homeostasis. It is also reported to bind RNA: it associates with structural motifs present in the 3′ untranslated regions of at least two transcripts, but the functional significance of this binding remains unknown. Although HAX‐1 has been detected in various cellular compartments, it is predominantly cytoplasmic. Our detailed localization studies of HAX‐1 isoforms revealed partial nuclear localization, the extent of which depends on the protein isoform. Further studies demonstrated that HAX‐1 is in fact a nucleocytoplasmic shuttling protein, dependent on the exportin 1 nuclear export receptor. Systematic mutagenesis allowed identification of the two nuclear export signals in the HAX‐1 sequence. HAX‐1 nuclear accumulation was observed after inhibition of nuclear export by leptomycin B, but also after specific cellular stress. The biological role of HAX‐1 nuclear localization and shuttling remains to be established, but the HAX‐1 transcript‐binding properties suggest that it may be connected to mRNA processing and surveillance. In this study, HAX‐1 status was shown to influence mRNA levels of DNA polymerase β, one of the HAX‐1 mRNA targets, although this effect becomes pronounced only after specific stress is applied. Moreover, HAX‐1 tethering to the reporter transcript caused a significant decrease in its expression. Additionally, the HAX‐1 co‐localization with P‐body markers, reported here, implies a role in mRNA processing. These results suggest that HAX‐1 may be involved in the regulation of expression of bound transcripts, possibly as part of the stress response.Structured digital HAX1andDCP1A,colocalizebyfluorescence microscopy(View Interaction:1,2) HAX1 physically interacts with XPO1 by anti tagcoimmunoprecipitation (View interaction)

The influence of the pH of the multicomponent cell medium on the performance of doxorubicin (DOX), an anticancer drug, was studied on the examples of cervical (HeLa) and kidney (A498) cancer cell lines. The change of pH of the cell medium to more acidic led to a decrease of DOX toxicity on both cell lines due to the change of drug permeability across the cell membrane as a result of drug protonation. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) studies and lactate dehydrogenase (LDH) release tests have shown low toxicity of the drug, especially in the case of A498 cells, which are characterized by an extremely high glycolytic metabolism. The behavior was ascribed primarily to the increased proton concentration in the peripheral blood follicle in the presence of products of the acidic glycolytic metabolism. It is not observed in the measurements performed in commercially available media since they usually have a neutral pH. In earlier reports on kidney cancer, several mechanisms were discussed, including the metabolism of DOX to its less toxic derivative, doxorubicinol, overexpression of ATP binding cassette subfamily B member 1 (ABCB1) transporters, that remove DOX from the inside of cells; however, there was no focus on the simple but very important contribution of drug protonation described in the present study. Drug pH-dependent equilibria in the cell medium should be considered since changes in the drug form may be an additional reason for multidrug resistance.