Impact of SLC20A1 on the Wnt/β-catenin signaling pathway in somatotroph adenomas

Abstract

Studies have revealed that genetic and functional aberrations of oncogenes, tumor-suppressor genes, signaling pathways and receptors are among the most prominent events in pituitary tumorigenesis, and a potent biomarker would be helpful for early diagnosis, subsequent treatment and disease control. The present study investigated the expression signatures of solute carrier family 20 member 1, also known as phosphate transporter 1 (SLC 20A1) and the Wnt/β-catenin signaling pathway in 52 patients with somatotroph adenomas. According to immunohistochemistry analysis, the H-score of SLC 20A1 was 222.6±15.2 in invasive tumor samples and 144.5±30.4 in non-invasive tumor samples (P<0.01), while the H-scores of β-catenin were 210.1±21.4 and 134.9±32.7, respectively (P<0.05). The H-scores of Wnt inhibitory factor 1 (Wif1) exhibited the opposite trend, with scores of 134.5±22.7 and 253.6±14.8, respectively (P<0.01). The H-scores of SLC 20A1 were negatively associated with those of Wif1 in somatotroph adenomas (correlation coefficient r=-0.367). The mean progression-free survival in the low SLC 20A1 group was longer than that in the group with high SLC20A1 H-scores (P=0.024). Reverse transcription-quantitative PCR (RT-qPCR) and western blotting confirmed the interference efficiency of the segments short hairpin (Sh)-B-SLC 20A1 and Sh-C- SLC 20A1. Cell proliferation experiments revealed that the cell viability of the Sh-B-SLC 20A1 group was 76.3±4.5, 65.7±3.7 and 53.1±3.2% of that of control GH3 cells after 24, 48 and 72 h of transfection, respectively, while the cell viability of the Sh-C- SLC 20A1 group was 86.4±5.7, 75.6±4.4 and 67.5±3.8%, respectively (P<0.05). ELI SA analysis demonstrated the growth hormone (GH) levels in the Sh-B-SLC 20A1 and Sh-C- SLC 20A1 groups to be 34.7±10.4 and 54.6±14.4%, respectively, of that of control GH3 cells (P<0.05). The transmembrane invasion assay revealed that knocking down SLC20A1 significantly suppressed cell invasion in the Sh-B-SLC 20A1 and Sh-C- SLC 20A1 groups. RT-qPCR and western blotting demonstrated that Sh-B-SLC 20A1 and Sh-C- SLC 20A1 evidently increased the levels of Wif1 and secreted frizzled-related protein 4. The present data suggested that SLC 20A1 levels are positively associated with tumor size, invasive behavior and tumor recurrence in somatotroph adenomas. Furthermore, SLC 20A1 may be associated with the activation of the Wnt/β-catenin signaling pathway.