In the past studies, it is shown that cardiac troponin I (cTnI, encoded by TNNI3), as a cytoplasmic protein, is an inhibitory subunit in troponin complex, and involves in cardiomyocyte diastolic regulation. Here, we assessed a novel role of cTnI as a nucleoprotein. Firstly, the nuclear translocation of cTnI was found in mouse, human fetuses and rat heart tissues. In addition, there were differences in percentage of intranuclear cTnI in different conditions. Based on weighted gene co-expression network analyses (WGCNA) and verification in cell experiments, a strong expression correlation was found between TNNI3 and Atp2a2, which encodes sarco-endoplasmic reticulum Ca²⁺ ATPase isoform 2a (SERCA2a), and involves in ATP hydrolysis and Ca²⁺ transient. TNNI3 gain and loss caused Atpa2a2 increase/decrease in a dose-dependent manner both in mRNA and protein levels, in vivo and in vitro. By using ChIP-sequence we demonstrated specific binding DNA sequences of cTnI were enriched in ATP2a2 promoter −239∼–889 region and the specific binding sequence motif of cTnI was analyzed by software as "CCAT", which has been reported to be required for YY1 binding to the promoter region of YY1-related genes. Moreover, it was further verified that pcDNA3.1 (−)-TNNI3 could express cTnI proteins and increase the promoter activity of Atp2a2 through luciferase report assay. In the end, we evaluated beat frequencies, total ATP contents, Ca²⁺ transients in TNNI3-siRNA myocardial cells. These findings indicated, for the first time, cTnI may regulate Atp2a2 in cardiomyocytes as a co-regulatory factor and participate in the regulation of intracellular Ca ions.

以往的研究表明，心肌肌钙蛋白I（cTnI，由TNNI3编码）作为一种细胞质蛋白，是肌钙蛋白复合物中的抑制亚基，参与心肌细胞舒张的调节。在这里，我们评估了 cTnI 作为核蛋白的新作用。首先，在小鼠、人类胎儿和大鼠心脏组织中发现了 cTnI 的核转位。此外，不同条件下核内cTnI的百分比存在差异。基于加权基因共表达网络分析 (WGCNA) 和细胞实验验证，发现TNNI3和Atp2a2之间存在强表达相关性，编码肌内质网 Ca ²⁺ ATPase 异构体 2a (SERCA2a)，参与 ATP 水解和钙²⁺瞬态。在体内和体外，TNNI3 的获得和损失导致 Atpa2a2 在 mRNA 和蛋白质水平上以剂量依赖性方式增加/减少。通过使用 ChIP 序列，我们证明 cTnI 的特异性结合 DNA 序列富含ATP2a2启动子 -239∼-889 区域，并且 cTnI 的特异性结合序列基序通过软件分析为“CCAT”，据报道这是YY1所必需的与YY1相关基因的启动子区域结合。此外，进一步证实 pcDNA3.1 (-)-TNNI3 可以表达 cTnI 蛋白并增加Atp2a2的启动子活性。通过荧光素酶报告测定。最后，我们评估了TNNI3 -siRNA 心肌细胞中的搏动频率、总 ATP 含量、Ca ²⁺瞬变。这些发现首次表明，cTnI可能作为辅助调节因子调节心肌细胞中的Atp2a2并参与细胞内Ca离子的调节。