Spatiotemporal aspects of calcium signalling

Ca2+-Dependent Transcriptional Repressors KCNIP and Regulation of Prognosis Genes in Glioblastoma

Glioblastomas (GBMs) are the most aggressive and lethal primary astrocytic tumors in adults, with very poor prognosis. Recurrence in GBM is attributed to glioblastoma stem-like cells (GSLCs). The behavior of the tumor, including proliferation, progression, invasion, and significant resistance to therapies, is a consequence of the self-renewing properties of the GSLCs, and their high resistance to chemotherapies have been attributed to their capacity to enter quiescence. Thus, targeting GSLCs may constitute one of the possible therapeutic challenges to significantly improve anti-cancer treatment regimens for GBM. Ca²⁺ signaling is an important regulator of tumorigenesis in GBM, and the transition from proliferation to quiescence involves the modification of the kinetics of Ca²⁺ influx through store-operated channels due to an increased capacity of the mitochondria of quiescent GSLC to capture Ca²⁺. Therefore, the identification of new therapeutic targets requires the analysis of the calcium-regulated elements at transcriptional levels. In this review, we focus onto the direct regulation of gene expression by KCNIP proteins (KCNIP1–4). These proteins constitute the class E of Ca²⁺ sensor family with four EF-hand Ca²⁺-binding motifs and control gene transcription directly by binding, via a Ca²⁺-dependent mechanism, to specific DNA sites on target genes, called downstream regulatory element (DRE). The presence of putative DRE sites on genes associated with unfavorable outcome for GBM patients suggests that KCNIP proteins may contribute to the alteration of the expression of these prognosis genes. Indeed, in GBM, KCNIP2 expression appears to be significantly linked to the overall survival of patients. In this review, we summarize the current knowledge regarding the quiescent GSLCs with respect to Ca²⁺ signaling and discuss how Ca²⁺via KCNIP proteins may affect prognosis genes expression in GBM. This original mechanism may constitute the basis of the development of new therapeutic strategies.

Intracellular Ca(2+)-handling differs markedly between intact human muscle fibers and myotubes

Background

In skeletal muscle, intracellular Ca²⁺ is an important regulator of contraction as well as gene expression and metabolic processes. Because of the difficulties to obtain intact human muscle fibers, human myotubes have been extensively employed for studies of Ca²⁺-dependent processes in human adult muscle. Despite this, it is unknown whether the Ca²⁺-handling properties of myotubes adequately represent those of adult muscle fibers.

Methods

To enable a comparison of the Ca²⁺-handling properties of human muscle fibers and myotubes, we developed a model of dissected intact single muscle fibers obtained from human intercostal muscle biopsies. The intracellular Ca²⁺-handling of human muscle fibers was compared with that of myotubes generated by the differentiation of primary human myoblasts obtained from vastus lateralis muscle biopsies.

Results

The intact single muscle fibers all demonstrated strictly regulated cytosolic free [Ca²⁺] ([Ca²⁺]_i) transients and force production upon electrical stimulation. In contrast, despite a more mature Ca²⁺-handling in myotubes than in myoblasts, myotubes lacked fundamental aspects of adult Ca²⁺-handling and did not contract. These functional differences were explained by discrepancies in the quantity and localization of Ca²⁺-handling proteins, as well as ultrastructural differences between muscle fibers and myotubes.

Conclusions

Intact single muscle fibers that display strictly regulated [Ca²⁺]_i transients and force production upon electrical stimulation can be obtained from human intercostal muscle biopsies. In contrast, human myotubes lack important aspects of adult Ca²⁺-handling and are thus an inappropriate model for human adult muscle when studying Ca²⁺-dependent processes, such as gene expression and metabolic processes.

Electronic supplementary material

The online version of this article (doi:10.1186/s13395-015-0050-x) contains supplementary material, which is available to authorized users.

Stimulus-secretion coupling and Ca2+ dynamics in pancreatic acinar cells

1. Unique spatiotemporal dynamics in cytosolic Ca2+ concentration, [Ca2+]c, were characterized in various cell types. In pancreatic acinar cells, physiological concentrations of cholecystokinin octapeptide, CCK-8, (< 10 pM) induce repetitive [Ca2+]c spikes commonly termed Ca2+ oscillation, whereas relatively higher concentrations (30 pM-1 nM) evoke biphasic [Ca2+]c dynamics; a rapid transient peak followed by a sustained increase. Much higher concentrations (> 1 nM) induce a large transient followed by a steep decay. 2. These [Ca2+]c dynamics correspond to secretory responses. Repetitive [Ca2+]c change is attributable to the upstroke of the bell-shaped dose-response relationship and the biphasic change is responsible for the downstroke of the relation (so called high-dose inhibited secretion). The large transient [Ca2+]c increase is associated with morphological changes such as bleb formation. 3. Possible interrelation between dose of secretagogues, secretory responses, [Ca2+]c dynamics, IP3 production, receptor occupation and morphological change will be discussed from both pharmacological and physiological points of view.