Calcium modulates calmodulin/α-actinin 1 interaction with and agonist-dependent internalization of the adenosine A2A receptor

Adenosine A2A Receptor Activation Enhances Blood-Tumor Barrier Permeability in a Rodent Glioma Model

The blood-tumor barrier (BTB) limits the entry of effective chemotherapeutic agents into the brain for treatment of malignant tumors like glioblastoma. Poor drug entry across the BTB allows infiltrative glioma stem cells to evade therapy and develop treatment resistance. Regadenoson, an FDA-approved adenosine A2A receptor (A2AR) agonist, has been shown to increase drug delivery across the blood-brain barrier in non-tumor-bearing rodents without a defined mechanism of enhancing BTB permeability. Here, we characterize the time-dependent impact of regadenoson on brain endothelial cell interactions and paracellular transport, using mouse and rat brain endothelial cells and tumor models. In vitro, A2AR activation leads to disorganization of cytoskeletal actin filaments by 30 minutes, downregulation of junctional protein expression by 4 hours, and reestablishment of endothelial cell integrity by 8 hours. In rats bearing intracranial gliomas, regadenoson treatment results in increase of intratumoral temozolomide concentrations, yet no increased survival noted with combined temozolomide therapy. These findings demonstrate regadenoson's ability to induce brain endothelial structural changes among glioma to increase BTB permeability. The use of vasoactive mediators, like regadenoson, which transiently influences paracellular transport, should further be explored to evaluate their potential to enhance central nervous system treatment delivery to aggressive brain tumors. IMPLICATIONS: This study provides insight on the use of a vasoactive agent to increase exposure of the BTB to chemotherapy with intention to improve glioma treatment efficacy.

Proteins with calmodulin-like domains: structures and functional roles

The appearance of modular proteins is a widespread phenomenon during the evolution of proteins. The combinatorial arrangement of different functional and/or structural domains within a single polypeptide chain yields a wide variety of activities and regulatory properties to the modular proteins. In this review, we will discuss proteins, that in addition to their catalytic, transport, structure, localization or adaptor functions, also have segments resembling the helix-loop-helix EF-hand motifs found in Ca2+-binding proteins, such as calmodulin (CaM). These segments are denoted CaM-like domains (CaM-LDs) and play a regulatory role, making these CaM-like proteins sensitive to Ca2+ transients within the cell, and hence are able to transduce the Ca2+ signal leading to specific cellular responses. Importantly, this arrangement allows to this group of proteins direct regulation independent of other Ca2+-sensitive sensor/transducer proteins, such as CaM. In addition, this review also covers CaM-binding proteins, in which their CaM-binding site (CBS), in the absence of CaM, is proposed to interact with other segments of the same protein denoted CaM-like binding site (CLBS). CLBS are important regulatory motifs, acting either by keeping these CaM-binding proteins inactive in the absence of CaM, enhancing the stability of protein complexes and/or facilitating their dimerization via CBS/CLBS interaction. The existence of proteins containing CaM-LDs or CLBSs substantially adds to the enormous versatility and complexity of Ca2+/CaM signaling.

Role of Alström syndrome 1 in the regulation of blood pressure and renal function

Elevated blood pressure (BP) and renal dysfunction are complex traits representing major global health problems. Single nucleotide polymorphisms identified by genome-wide association studies have identified the Alström syndrome 1 (ALMS1) gene locus to render susceptibility for renal dysfunction, hypertension, and chronic kidney disease (CKD). Mutations in the ALMS1 gene in humans causes Alström syndrome, characterized by progressive metabolic alterations including hypertension and CKD. Despite compelling genetic evidence, the underlying biological mechanism by which mutations in the ALMS1 gene lead to the above-mentioned pathophysiology is not understood. We modeled this effect in a KO rat model and showed that ALMS1 genetic deletion leads to hypertension. We demonstrate that the link between ALMS1 and hypertension involves the activation of the renal Na+/K+/2Cl- cotransporter NKCC2, mediated by regulation of its endocytosis. Our findings establish a link between the genetic susceptibility to hypertension, CKD, and the expression of ALMS1 through its role in a salt-reabsorbing tubular segment of the kidney. These data point to ALMS1 as a potentially novel gene involved in BP and renal function regulation.