Calmodulin-controlled spatial decoding of oscillatory Ca2+ signals by calcineurin

Abstract

Calcineurin is responsible for mediating a wide variety of cellular processes in response to dynamic calcium (Ca2+) signals, yet the precise mechanisms involved in the spatiotemporal control of calcineurin signaling are poorly understood. Here, we use genetically encoded fluorescent biosensors to directly probe the role of cytosolic Ca2+ oscillations in modulating calcineurin activity dynamics in insulin-secreting MIN6 β-cells. We show that Ca2+ oscillations induce distinct temporal patterns of calcineurin activity in the cytosol and plasma membrane vs at the ER and mitochondria in these cells. Furthermore, we found that these differential calcineurin activity patterns are determined by variations in the subcellular distribution of calmodulin (CaM), indicating that CaM plays an active role in shaping both the spatial and temporal aspects of calcineurin signaling. Together, our findings provide new insights into the mechanisms by which oscillatory signals are decoded to generate specific functional outputs within different cellular compartments.DOI: http://dx.doi.org/10.7554/eLife.03765.001

Calcineurin signaling in the heart: The importance of time and place

“…The CaNAR reporter is based on the regulatory domain of NFAT tagged on opposing ends with a cyan and a yellow fluorescent protein. Dephosphorylation by calcineurin causes a conformational change that increases FRET transfer between the two ends [17]. This can be combined with a Ca 2+ sensor to integrate Ca 2+ dynamics with processing of a specific calcineurin substrate.…”

“…This can be combined with a Ca 2+ sensor to integrate Ca 2+ dynamics with processing of a specific calcineurin substrate. Targeting this reporter to the cytosol, plasma membrane, mitochondria, or the ER, has been used to demonstrate that activation of the reporter in response to the same Ca 2+ signal can be very different in different regions of a cell [17]. For instance, in a pancreatic β cell line, the cytoplasmic and plasma membrane reporter displayed a single, integrated response to an oscillatory Ca 2+ input.…”

“…For instance, in a pancreatic β cell line, the cytoplasmic and plasma membrane reporter displayed a single, integrated response to an oscillatory Ca 2+ input. In contrast, the ER and mitochondrial reporter oscillated directly in concert with the Ca 2+ transient due to limited calmodulin availability proximal to the ER and rapid reversal of the reporter by cAMP activated protein kinase A (PKA) phosphorylation [17]. …”

“…It is not completely understood how calcineurin avoids beat-to-beat activation. However, many factors are likely involved, including the rate of association with calmodulin and regional differences in availability of this accessory protein [17]. An important concept that has immerged is the role of signaling microdomains that are define by the local concentrations of Ca 2+ , calmodulin, and target substrate [18–20].…”

The ins and outs of adrenergic signaling

“…Thus, the amplitude and the frequency as well as the spatial distribution (see below) of calcium oscillations may encode a specific downstream response [85]. For example, activation of calcineurin in an insulin-producing cell line has been demonstrated to be controlled by calmodulin in a way that allows oscillatory signals to generate specific functional outputs within different cellular compartments [86]. Furthermore, it has recently been shown that different isoforms of the transcription factor NFAT are specifically activated by distinct patterns of calcium signals [87].…”