Role of calreticulin in the regulation of long non-coding RNA: MALAT-1 expression in mouse adenocarcinoma cells

Abstract

Calreticulin (CRT) is a ubiquitously expressed protein in mammalian cells, with both calcium binding and chaperone activity. As such CRT is involved in quality control process during the folding and maturation of proteins in endoplasmic reticulum. Recent research in our lab showed that overexpression of CRT under control of Tie-2 promoter resulted in the development of metastatic lung adenocarcinoma. In order to examine genes involved in the development of lung cancer we carried out microarray analysis on RNA isolated from mouse lung tumors versus control lungs. In this screen we observed a significant increase (over 2 fold) in Metastasis Associated Lung Adenocarcinoma Transcript-1 (MALAT-1) long noncoding RNA (LncRNA) in the lungs of CRT overexpressing mouse models. MALAT-1 has been documented to be up-regulated in the human lung adenocarcinoma. This LncRNA has been shown to be associated with metastasis. Thus the aim of our study was to investigate the mechanism of regulation of MALAT-1 expression and role of CRT in this process. No data is available on the mechanism of regulation of MALAT-1 expression. We hypothesized that CRT as a regulator of intracellular calcium homeostasis regulated MALAT-1 expression thus inducing the development of metastatic lung adenocarcinoma in our mice model. Our data showed a significant correlation between intracellular calcium levels and expression and stability of MATAT-1 RNA level as determined using quantitative real time PCR. Treatment of adenocarcinoma cells with BAPTA-AM (to reduce intracellular calcium) resulted in a significant reduction in MALAT-1 level. Furthermore, treating the cells with thapsigargin (to elevate intracellular calcium) induced a 2 fold increase in MALAT-1 expression. We also demonstrated that knock down of MALA-1 expression using specific siRNA reduces the proliferation of adenocarcinoma cell derived from our CRT overexpressing mouse. Our data demonstrate for the first time involvement of calcium binding protein CRT and intracellular level of calcium on expression and stability of MALAT-1 that is involved in development of lung adenocarcinoma. This research was funded by Qatar National Research Fund (NPRP4-043-3-016).