The roles of serum PDCD5 in circulating CD133 positive cells of the patients with gastric cancer

SLC34A2 regulates miR-25-Gsk3β signaling pathway to affect tumor progression in gastric cancer stem cell-like cells

A novel paradigm in tumor biology suggests that gastric cancer progression is driven by gastric cancer stem cell-like cells (GCSCs), but molecular mechanisms regulating tumorigenic and self-renewal potential of GCSCs are still unclear. Here, we aim to investigate biological function of SLC34A2 in regulating sphere formation and tumorigenicity (both are the hallmark of CSCs) of GCSCs and its underlying mechanisms. Our findings testified that CD44⁺ cells which were derived from fresh primary gastric cancer samples and cell lines displayed stem cell-like features. Significantly, SLC34A2 is increased in CD44⁺ GCSCs compared with those in adherent counterpart from CD44⁺ GCSCs. On clinic, SLC34A2 is overexpressed in primary tumor tissues compared with adjacent counterparts. We showed that SLC34A2 regulated sphere formation and self-renewal properties of CD44⁺ GCSCs in vitro and in vivo. Mechanistic investigations revealed that Gsk3β was the most strikingly up-regulated gene in response to SLC34A2 knockdown in GCSCs and Wnt/β-cantenin signaling was required for SLC34A2-mediated sphere formation. Furthermore, SLC34A2 directly binds specific sites in the miR-25 promoter region and that the promoter activity is decreased after the mutation of putative SLC34A2-binding sites, indicating that SLC34A2 is required for the transcriptional induction of miR-25. Meanwhile, luciferase assays showed that miR-25 directly targeted Gsk3β in CD44⁺ GCSCs. Overall, our findings define a SLC34A2-miR-25-Gsk3β pathway in the regulation of GCSCs features and gastric cancer progression, with potential therapeutic applications in blocking their progression.

PDCD5 regulates cell proliferation, cell cycle progression and apoptosis

Programmed cell death (PDCD)5 is cloned from human leukemia cell line TF-1. PDCD5 is one of the members of the programmed cell death protein family that is frequently involved in tumor growth and apoptosis. To investigate the molecular and cellular functions of PDCD5, the present study established a PDCD5 stably overexpressing A431 cell line and examined the role of PDCD5 in cell proliferation, cell cycle progression and apoptosis. The data demonstrated that overexpression of PDCD5 significantly inhibited cell proliferation, induced cell cycle arrest at G2/M phase and apoptosis in A431 cells. The expression profiles of certain key regulators of these cellular events were further investigated, including P53, B cell lymphoma (BCL)-2, BCL-2 associated X protein (BAX) and caspase (CASP)3. The data demonstrated that at the transcript and protein levels, P53, BAX and CASP3 were all upregulated in the PDCD5 stably overexpressing A431 cells whereas BCL-2 was downregulated, indicating that PDCD5 acts as an important upstream regulator of P53, BCL-2, BAX and CASP3. The data suggest that PDCD5 regulates cell proliferation, cell cycle progression and apoptosis in A431 cells. PDCD5 may be a novel tumor suppressor gene, and may be potentially used for cancer treatment in the future.

Upregulated miR-132 in Lgr5+ gastric cancer stem cell-like cells contributes to cisplatin-resistance via SIRT1/CREB/ABCG2 signaling pathway

Cisplatin resistance has long been a major problem that restricts its use. A novel paradigm in tumor biology suggests that gastric tumor chemo-resistance is driven by gastric cancer stem cell-like (GCSCs). Growing evidence has indicated that microRNAs (miRNAs) contributes to chemo-resistance in gastric cancer (GC). Here, Lgr5⁺ cells derived from gastric cancer cell lines displayed stem cell-like features. Flow cytometry demonstrated the presence of a variable fraction of Lgr5 in 19 out of 20 GC specimens. By comparing the miRNA expression profiles of Lgr5⁺ GCSCs and Lrg5^- cells, we established the upregulation of miR-132 in Lgr5⁺ GCSCs. The enhanced miR-132 expression correlated chemo-resistance in GC patients. Kaplan-Meier survival curve showed that patients with low miR-132 expression survived obviously longer. Functional assays results indicated that miR-132 promoted cisplatin resistance in Lgr5⁺ GCSCs in vitro and in vivo. Further dual-luciferase reporter gene assays revealed that SIRT1 was the direct target of miR-132. The expression of miR-132 was inversely correlated with SIRT1 in gastric cancer specimens. Furthermore, through PCR array we discovered ABCG2 was one of the downstream targets of SIRT1. Overexpression of SIRT1 down-regulated ABCG2 expression by promoting the de-acetylation of the transcription factor CREB. CREB was further activated ABCG2 via binding to the promoter of ABCG2 to induce transcription. Thus, we concluded that miR-132 regulated SIRT1/CREB/ABCG2 signaling pathway contributing to the cisplatin resistance and might serve as a novel therapeutic target against gastric cancer.