Abstract 463: Evaluation of relative expression of SLC34A2/NaPi-IIb in lung cancer cell lines treated with estrogen and PKC and PKA pathway modulators

Abstract

Abstract Background: Lung cancer (LC) represents a major health challenge worldwide, being the leading cause of cancer-related deaths in both men and women. SLC34A2 is a member of the solute carrier family and encodes the type IIb sodium phosphate cotransporter (NaPi-IIb). SLC34A2 expression is reduced by ten-fold in LC samples compared to normal lung. Estrogen is a known risk factor for LC in women, and a relationship between its action and SLC34A2/NaPi-IIb super-expression in certain cell lines has been proposed. Furthermore, based on the central role of PKC isoenzymes in carcinogenesis, and on studies showing that administration of cAMP stimulates the NaPi-IIb mRNA expression in adult rats alveolar type II cells, this work aimed to evaluate the correlation between PKA (cAMP mediator), PKC, estrogen signaling pathways and SLC34A2/NaPi-IIb expression levels in human LC cells. Methods: For both LC cell lines studied, A549 and H460, the effects of PKC and PKA activating and inhibitory reagents (PMA, calphostin C, dB cAMP and KT 5720) were tested in relation to SLC34A2/NaPi-IIb expression. Additionally, a dose-response curve of 17-beta-estradiol was performed for the expression of SLC34A2/NaPi-IIb in A549 cell line. SLC34A2/NaPi-IIb gene expression was analyzed by qRT-PCR, using SYBR Green PCR Master Mix as the detection system. Relative quantification of gene expression was performed by calculating the delta-delta Ct using two housekeeping genes: GAPDH and Beta-Actin. Findings: In our analysis we found that PKC and PKA did not influence the expression of SLC34A2/NaPi-IIb in LC cell line evaluated. There was, however, a considerable increase in the expression of this gene when treated with calphostin C, probably by a mechanism independent of its classic role in the PKC inhibition. There was also a trend of decreased SLC34A2/NaPi-IIb gene expression in LC cell line following the treatment with 17 beta-estradiol, and SLC34A2/NaPi-IIb - which expression is already reduced in LC - undergoes a greater reduction in its relative expression. Interpretation: We believe that maintaining the reduced expression of SLC34A2/NaPi-IIb should provide benefits to LC cells. Calphostin C induces apoptosis in several tumor cell lines by mechanisms not yet fully elucidated. Thus, we suggest a possible involvement of SLC34A2/NaPi-IIb in this pro-apoptotic pathway, which corroborates the fact that LC tumors present a reduced SLC34A2/NaPi-IIb expression compared to normal lung. Likewise, based on our findings, we believe that the inclusion of selective Estrogen receptor modulators and aromatase inhibitors in the routine clinical practice of LC might help to control the disease that is still the leading cause of cancer-related deaths worldwide. Citation Format: Murilo F. Cerri, Lucas C d Rezende, Marcela F. Paes, Klesia P. Madeira, Renata D. Daltoe, Nayara G. Tessarollo, Ian V. Silva, Leticia B a Rangel. Evaluation of relative expression of SLC34A2/NaPi-IIb in lung cancer cell lines treated with estrogen and PKC and PKA pathway modulators. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 463. doi:10.1158/1538-7445.AM2014-463