The Sarco/Endoplasmic Reticulum Ca -ATPases (SERCAs), pump Ca into the endoplasmic reticulum lumen modulating cytosolic Ca concentrations to regulate various cellular processes including cell growth. Previous studies have reported a downregulation of SERCA3 protein expression in gastric and colon cancer cell lines and showed that in vitro cell differentiation increases its expression. However, little is known about the transcriptional mechanisms and transcription factors that regulate SERCA3 expression in epithelial cancer cells. In this work, we demonstrate that SERCA3 mRNA is upregulated up to 45-fold in two epithelial cancer cell lines, KATO-III and Caco-2, induced to differentiate with histone deacetylase inhibitors (HDACi) and by cell confluence, respectively. To evaluate the transcriptional elements responding to the differentiation stimuli, we cloned the human ATP2A3 promoter, generated deletion constructs and transfected them into KATO-III cells. Basal and differentiation responsive DNA elements were located by functional analysis within the first -135 bp of the promoter region. Using site-directed mutagenesis and DNA-protein binding assays we found that Sp1, Sp3, and Klf-4 transcription factors bind to ATP2A3 proximal promoter elements and regulate basal gene expression. We showed that these factors participated in the increase of ATP2A3 expression during cancer cell differentiation. This study provides evidence for the first time that Sp1, Sp3, and Klf-4 transcriptionally modulate the expression of SERCA3 during induction of epithelial cancer cell differentiation. © 2016 Wiley Periodicals, Inc.

Recent studies have shown that expression of Sarco(endo)plasmic Reticulum Ca(2+) -ATPase 2 (SERCA2) is decreased in oral cancer; whereas expression of SERCA3 is considerably decreased or absent in human colon, gastric, breast, and lung cancers. The ATP2A2 and ATP2A3 genes encode SERCA2 and SERCA3 isoforms, respectively. Promoter methylation on CpG islands was responsible for the repression of ATP2A2 gene in human oral cancer samples. On the other hand, histone deacetylase inhibitors (HDACi) up-regulate ATP2A3 expression in gastric, colon, and lung cancer cells in culture, however, the molecular mechanism is unknown. In this study, we investigate whether HDACi and DNA methylation regulate ATP2A2 and ATP2A3 expression in human breast cancer cell lines. Results show a marked induction of SERCA3a and pan-SERCA3 mRNA expression in human MCF-7 and MDA-MB-231 cells treated with sodium butyrate (NaB) or trichostatin A (TSA); whereas SERCA2b mRNA expression did not change significantly. ChIP assays show that NaB or TSA treatment of MDA-MB-231 cells increases H3K9 acetylation on ATP2A3 promoter. NaB also decreases H3K9 trimethylation; suggesting that these modifications stimulate ATP2A3 gene expression, through a chromatin remodeling mechanism. In contrast, NaB or TSA do not increase H3K9-acetylation of ATP2A2 proximal promoter. In addition, treatment with 5-aza-2'-deoxycytidine did not affect SERCA2b and SERCA3a expression, suggesting that promoter methylation status does not alter their expression in these cell lines. We propose that alteration of SERCA2b/SERCA3a isoform expression ratio could affect calcium management within the cell, and thus, the cellular pathways regulated by calcium could be compromised, such as cellular proliferation or apoptosis. © 2015 Wiley Periodicals, Inc.

Abstract. Period circadian regulator (Per)1 and Per2 genes are involved in the molecular mechanism of the circadian clock, and exhibit tumor suppressor properties. Several studies have reported a decreased expression of Per1, Per2 and Per3 genes in different types of cancer and cancer cell lines. Promoter methylation downregulates Per1, Per2 or Per3 expression in myeloid leukemia, breast, lung, and other cancer cells; whereas histone deacetylase inhibitors (HDACi) upregulate Per1 or Per3 expression in certain cancer cell lines. However, the transcriptional regulation of Per1 and Per2 in cancer cells by chromatin modifications is not fully understood. The present study aimed to determine whether HDACi regulate Per1 and Per2 expression in gastric cancer cell lines, and to investigate changes in chromatin modifications in response to HDACi. Treatment of KATO III and NCI-N87 human gastric cancer cells with sodium butyrate (NaB) or Trichostatin A (TSA) induced Per1 and Per2 mRNA expression in a dose-dependent manner. Chromatin immunoprecipitaion assays revealed that NaB and TSA decreased lysine 9 trimethylation on histone H3 (H3K9me3) at the Per1 promoter. TSA, but not NaB increased H3K9 acetylation at the Per2 promoter. It was also observed that binding of Sp1 and Sp3 to the Per1 promoter decreased following NaB treatment, whereas Sp1 binding increased at the Per2 promoter of NaB-and TSA-treated cells. In addition, Per1 promoter is not methylated in KATO III cells, while Per2 promoter was methylated, although NaB, TSA, and 5-Azacytidine do not change the methylated CpGs analyzed. In conclusion, HDACi induce Per1 and Per2 expression, in part, through mechanisms involving chromatin remodeling at the proximal promoter of these genes; however, other indirect mechanisms triggered by these HDACi cannot be ruled out. These findings reveal a previously unappreciated regulatory pathway between silencing of Per1 gene by H3K9me3 and upregulation of Per2 by HDACi in cancer cells.

The knowledge about the role of calcium‐regulated pathways in cancer cell growth and differentiation could be useful for the development of new therapeutic approaches to diminish its mortality. The ATP2A genes encode for SERCA pumps, which modulate cytosolic Ca2+ concentration, regulating various cellular processes including cell growth. ATP2A3 gene transcriptional down‐regulation has been reported in gastric and colon cancer, but there is still a lack of understanding about the epigenetic processes regulating its transcription. In this work, we report that butyrate, trichostatin A, and 5‐azacytidine treatments increase SERCA3 expression, increased apoptosis, and decreased cell viability of the KATO‐III gastric carcinoma cell line. We analyzed the methylation profile of the ATP2A3 gene promoter CpG island, finding clones with methylated status through −280 to −135 promoter region, harboring Sp1 and AP‐2 binding sites, which could have a role in transcriptional repression. Post‐translational modifications of histones show a major role in the ATP2A3 transcriptional regulation, and our results show histones marks linked to transcriptional repression associated with the −262 to −135 region, this repressive context changed to transcriptional permissive through SERCA3 re‐expressing conditions. These results suggest that the nucleotide sequence from −280 to −135 position is an ATP2A3 epigenetic regulatory CpG region in KATO‐III cells. Analyses of online‐databases show a decreased SERCA3 expression in gastric and colon tumors, as well as overall survival results, showed that high SERCA3 expression could serve as a favorable prognostic marker for colon and gastric cancer patients.

The sarco(endo)plasmic reticulum Ca2+‐ATPase, ATP2A3 gene, is highly expressed in gastrointestinal cells, but is selectively lost in cancer. Previously, was reported that SERCA3 protein is induced when human gastric and colon cancer cells undergo in vitro differentiation. In this work, we induced differentiation of gastric and colon cancer cells in culture, finding increased SERCA3 mRNA expression and increased transcriptional activity of hATP2A3‐gene‐promoter constructs (up to 50‐fold) after induced differentiation, narrowing the responsive elements within ‐ 135 to +142 bp 5’‐region of the human ATP2A3 promoter containing 8 consensus Sp‐factors binding sites, which previously have shown an important role in the transcriptional regulation of the gene. KLF4 transcription factor is decreased in gastric and colon cancer in a similar pattern to that of SERCA3, and both increase after induced differentiation. In EMSA assays, we found that KLF4 binding increases in differentiated cancer cell lines, suggesting that might function as an activator of ATP2A3 expression. In contrast, the results suggest that Sp3 functions as a repressor in tumor cells keeping low SERCA3 expression. By ChIP assays we found that KLF4 binds to the proximal ATP2A3 promoter as part of a co‐activator complex with the histone‐acetyltransferase p300, regulating positively the transcription of ATP2A3. Supported by grant PAPIIT IN213613.