GO:1902081 negative regulation of calcium ion import into sarcoplasmic reticulum

Calcium ions (Ca2+) are universal second messengers that control muscle contraction, secretion, gene expression, and cell survival. The sarcoplasmic reticulum (SR) is a specialized endoplasmic reticulum (ER) compartment that stores and releases Ca2+ during excitation-contraction coupling and signaling. The import of Ca2+ into the SR is mediated primarily by sarco/endoplasmic reticulum Ca2+-ATPases (SERCAs), while release occurs through ryanodine receptors (RyRs) and inositol 1,4,5-trisphosphate receptors (IP3Rs). The Gene Ontology term GO:1902081, negative regulation of calcium ion import into sarcoplasmic reticulum, captures the regulatory processes that reduce the rate or extent of SERCA-mediated Ca2+ uptake into the SR. This regulation is critical because excessive or prolonged SR Ca2+ import can deplete cytosolic Ca2+ signals, alter ER/SR luminal Ca2+ stores, and trigger ER stress or arrhythmogenic events. Conversely, insufficient SR Ca2+ import impairs muscle relaxation and ER chaperone function. Understanding the molecular players that negatively regulate SR Ca2+ import is therefore central to muscle physiology, cardiac disease, and neurobiology. Researchers study this process using genetically engineered cell and animal models, live-cell Ca2+ imaging, and biochemical assays of SERCA activity. The redox environment of the ER/SR is a key modulator; for example, the disulfide reductase ERdj5 (DNAJC10) influences ER Ca2+ homeostasis by regulating the redox state of calcium-handling proteins. This article provides a research-grade overview of GO:1902081, its mechanisms, key genes, disease links, and the CRISPR-based methods used to investigate it.

GO:1902081 is a biological process term defined as any process that stops, prevents, or reduces the frequency, rate, or extent of calcium ion import into the sarcoplasmic reticulum. In practice, it encompasses molecular events that inhibit SERCA pump activity, reduce SERCA-mediated Ca2+ uptake, or otherwise lower the net flux of Ca2+ from the cytosol into the SR lumen. This term is distinct from positive regulation (GO:1902080) and from regulation of calcium release from the SR.

GO:1902081 is important because the sarcoplasmic reticulum is the primary intracellular Ca2+ store, and the balance between Ca2+ import and release determines the amplitude, duration, and spatial pattern of cytosolic Ca2+ signals. Negative regulation of SR Ca2+ import prevents excessive Ca2+ sequestration that could blunt signaling or cause luminal Ca2+ overload, and it is a point of convergence for redox, metabolic, and stress signals. Dysregulation of this process is linked to cardiac arrhythmias, heart failure, and muscle weakness. Thus, understanding the negative regulators of SR Ca2+ import offers therapeutic targets and mechanistic insights into calcium-related diseases.

The following genes and proteins are experimentally implicated in the regulation of calcium ion import into the sarcoplasmic reticulum, with ERdj5 (DNAJC10) as a validated redox regulator.

The negative regulation of calcium ion import into the sarcoplasmic reticulum is itself regulated at multiple levels. Redox conditions in the ER/SR lumen control the activity of ERdj5 and other disulfide-modifying enzymes, which in turn affect SERCA function. Phosphorylation of phospholamban by PKA or CaMKII relieves SERCA inhibition, thereby increasing SR Ca2+ import; dephosphorylation reverses this effect. Hormonal and stress signals, including beta-adrenergic stimulation and ER stress, alter the expression and activity of SERCA, PLN, SLN, and ERdj5. Feedback from luminal Ca2+ and ER stress sensors (PERK, ATF6, IRE1) further tunes the rate of SR Ca2+ import to match cellular demand.

Dysregulated SR Ca2+ import contributes to abnormal Ca2+ cycling in cardiomyocytes, which can trigger arrhythmias and impair contractility in heart failure. Negative regulators such as phospholamban and ERdj5 influence SERCA activity and SR Ca2+ load, and their dysfunction has been linked to cardiac pathology.

In skeletal muscle, altered SR Ca2+ import can lead to weakness, fatigue, and myopathy. Mutations or altered expression of SERCA1, sarcolipin, or ERdj5 may disrupt Ca2+ homeostasis and contribute to muscle disease.

Because the ER and SR share Ca2+ handling machinery, negative regulation of SR Ca2+ import affects ER stress and the unfolded protein response. Chronic ER stress is implicated in diabetes, neurodegeneration, and inflammatory diseases.

Fluorescent Ca2+ indicators (e.g., Fura-2, Fluo-4, genetically encoded sensors) are used to measure cytosolic and SR Ca2+ dynamics in real time. This method directly reports the effects of negative regulators on SR Ca2+ import.

Biochemical assays using SR vesicles or purified SERCA measure ATP hydrolysis and Ca2+ uptake rates. These assays quantify the impact of regulatory proteins such as PLN, SLN, and ERdj5 on SR Ca2+ import.

Redox-sensitive probes and Western blotting for disulfide-bonded SERCA can assess the role of ERdj5 and other redox regulators in modulating SR Ca2+ import.

Genome-wide CRISPR knockout or activation screens coupled with Ca2+ reporters can identify novel negative regulators of SR Ca2+ import.

Researchers studying negative regulation of calcium ion import into sarcoplasmic reticulum-related genes often need to determine whether a candidate gene is causally involved in this process. EDITGENE provides end-to-end CRISPR services to generate precisely engineered cell models for such investigations.

GO:1902081, negative regulation of calcium ion import into sarcoplasmic reticulum, is a critical biological process that fine-tunes intracellular Ca2+ signaling and protects against Ca2+ overload. The redox regulator ERdj5 (DNAJC10) exemplifies how disulfide chemistry controls SERCA function and ER/SR Ca2+ homeostasis. Dysregulation of this process is implicated in cardiac, skeletal muscle, and ER stress-related diseases. Advances in CRISPR-based genome editing and Ca2+ imaging now enable precise interrogation of the genes and mechanisms that negatively regulate SR Ca2+ import, offering new avenues for therapeutic intervention.