Our findings demonstrated that the expression level of full

Our findings demonstrated that the expression level of full-length α1 sGC protein was higher in the malignant and benign breast tumors than that of normal tissues. Similarly, an increase in the expression of α1 sGC subunit has been detected in glioma cell lines [34]. Higher expressions of sGCα1 and sGCβ1 have also been shown in the breast cancer cell line, MDA-MB-468 [35]. In the present study, the expression of different alternative splicing forms have been evaluated in the malignant, benign and corresponding normal breast tissues. The expression of six, out of 13, different splice forms have been detected, three for α1 and three for β1 sGC. The presence of three alternative α1 sGC splice transcripts have been reported in human heart, brain, artery, and Bcells [36]. Our results revealed that sGC mRNA expressions of Tr7 and Tr6 for α1 subunits in the malignant breast tumor were significantly lower than those of normal and benign tissues, no significant differences were observed between benign and normal tissues. In the present investigation, mRNA expressions of Tr3 in the malignant tumor was found to be higher than those of benign and normal breast tissues which could be explained by the elevation of cGMP in the breast cancer [37,38]. No significant changes were found in the benign tumors when compared to those of normal tissues. On the contrary in an investigation in aortas with aneurysm disease, using the same methods as ours (RT-PCR), a much higher level of transcripts coding for α1-IsoD (Tr7) and α1-IsoC (Tr6) splice variants have been obtained [18]which results in the reduction of cGMP in this disorder. Transcript 6, isoform C (N1-α1 variant) encodes α1 sGC protein with extensive deletion in the catalytic domain and inhibits the activity of α1/β1 sGC [24]. Transcript 7, isoform D, is also produced by an alternative splicing in polyadenylation site on exon 10 [39]. This mRNA isoform encodes an aberrant polypeptide that missing 66 amino 2-Guanidinoethylmercaptosuccinic Acid residues at the C-terminal (39). The deletion which is located in close proximity to the catalytic domain, might affect the catalytic properties of sGC's α1 subunit [39]. Concerning Transcript 5, sGC's α1 subunit in the present investigation, no expression has been detected. However, in an in vitro study using cancer cell lines, high expression of Tr5 of α1 has been found by Cote et al. They showed that an alternative splicing could be changed by antioxidant balance in the presence of H2O2, [25]. The results of present study revealed that Tr1 and Tr2 expressions, related to β1 sGC, in the malignant tumors were lower than those of benign and normal breast tissues, no significance differences were observed for Tr4, sGC's β1. Similarly, no expressions were detected for Tr3, Tr5 and Tr6 sGC's β1. Our results are validated by the facts that proteins encoded by alternative transcripts β1-Tr 3, 5, and 6 are expected to be dysfunctional since, they have missing regions in the catalytic domain or deletions/insertions in the heme-binding region [18], although Tr1 and Tr2 expressions observed in the present study, are essential for the enzyme activity. In an initial study, two different mRNA for β1 sGC expression have been detected in the human lung tissue [40]. An increase in α1 and a decrease in β1 expressions have also been shown in the present study. These results are validated by Cabilla eat al findings [41], since, they have demonstrated that estrogen can regulate sGC/cGMP pathway by a decrease in β1 and an increase in α1 expressions in some tissues.
Declarations of interest
Funding This work was supported by a Ph.D. grant from Tarbiat Modares University and also by Iranian National Science Foundation (INSF Code: 95848857).
Ethics approval All procedures performed in this study were approved by the Tarbiat Modares University Ethics Committee and in accordance with the ethical standards of 1964 Helsinki declaration and its later amendments or comparable ethical standards.