HAX1: A versatile, intrinsically disordered regulatory protein.

HAX1 is a relatively small, ubiquitously expressed, predominantly mitochondrial, intrinsically disordered protein. It has been implicated in the regulation of apoptosis, cell migration, calcium cycling, proteostasis, angiogenesis, autophagy and translation. A wide spectrum of functions, numerous interactions and still elusive molecular mechanisms of action make HAX1 an intriguing subject of research. Moreover, HAX1 is involved in the pathogenesis of diseases; its deficiency leads to neutropenia and its overexpression is associated with cancer. In this review we aim to describe the characteristics of HAX1 gene and protein, and comprehensively discuss its multiple functions, highlighting the emerging role of HAX1 in protection from stress and apoptosis through maintaining cellular proteostasis and homeostasis.

Water-soluble galactosamine derivative of ß-cyclodextrin as protective ligand and targeted carrier for delivery of toxic anthracycline drug.

ß-cyclodextrin modified with an electron-rich aromatic triazole linker and targeting moiety (galactosamine) was synthesized and studied as a carrier for the anticancer drug, doxorubicin (DOX), with the aim of targeting the pathological cells, reducing the cardiotoxic side effects and increasing the binding of the drug to DNA. The ß-cyclodextrins modified with galactosamine (ßCDGAL) are non-toxic and highly soluble in aqueous medium compared to the native ßCD and ßCD modified only with aromatic moiety, such as triazole linker. Molecular modelling and NMR study gave a deeper insight into the ligand structure, providing an explanation for its increased solubility, and the drug-ligand interactions. The triazole linker strengthened the drug binding and introduced pH dependence of the complex stability constants for ßCDGAL derivative, as confirmed by the voltammetry measurements. Spectroscopic studies have shown that entrapment of the DOX in ßCDGAL cavity reduces the stability constant of the DOX:Fe(III) complex responsible for the production of cardiotoxic reactive oxygen species and additionally supports the binding of the drug to the double strand DNA. The MTT assay and confocal microscopy results showed that despite encapsulation of the drug in the cyclodextrin molecule, its cytotoxic effect on the liver cancer cell line (HepG2) is comparable to that of the free, non-protected drug.

Impact of Medium pH on DOX Toxicity toward HeLa and A498 Cell Lines.

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.

HAX1 impact on collective cell migration, cell adhesion, and cell shape is linked to the regulation of actomyosin contractility.

HAX1 protein is involved in the regulation of apoptosis, cell motility and calcium homeostasis. Its overexpression was reported in several tumors, including breast cancer. This study demonstrates that HAX1 has an impact on collective, but not single-cell migration, thus indicating the importance of cell-cell contacts for the HAX1-mediated effect. Accordingly, it was shown that HAX1 knockdown affects cell-cell junctions, substrate adhesion, and epithelial cell layer integrity. As demonstrated here, these effects can be attributed to the modulation of actomyosin contractility through changes in RhoA and septin signaling. Additionally, it was shown that HAX1 does not influence invasive potential in the breast cancer cell line, suggesting that its role in breast cancer progression may be linked instead to collective invasion of the epithelial cells but not single-cell dissemination.

Cytoplasmic HAX1 Is an Independent Risk Factor for Breast Cancer Metastasis.

HAX1 is an antiapoptotic factor involved in the regulation of cell migration and calcium homeostasis, overexpressed in several cancers, including breast cancer. It has been suggested that HAX1 is also implicated in metastasis. Herein we report the results of meta-analysis of HAX1 expression, based on publicly available data, which confirms its significant overexpression in breast cancer and demonstrates copy number gain and prognostic value of HAX1 overexpression for metastatic relapse in ER+ tumors. IHC analysis reported here also reveals its significant overexpression in breast cancer samples from primary tumors, indicating significantly higher HAX1 protein levels in a group of patients who developed distant metastases in a disease course. Moreover, we demonstrate that HAX1 localization is important for the prediction of metastatic relapse and that cytoplasmic but not nuclear HAX1 is an independent risk factor for breast cancer metastasis.

Resistance to endocrine therapy in breast cancer: molecular mechanisms and future goals.

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.