Na-Pi cotransporter expressed during the differentiation of pancreatic AR42J cells

MicroRNA-410 acts as oncogene in NSCLC through downregulating SLC34A2 via activating Wnt/β-catenin pathway

SLC34A2 had been reported to be down-regulated in human NSCLC cells and patient tissues, and played a significant role in lung cancer. However, the mechanism of its unusual expressionin NSCLC has not been fully elucidated. In present study, we identified SLC34A2 was a direct target of miR-410 and could be inhibited by miR-410 transcriptionally and post-transcriptionally. MiR-410 promoted the growth, invasion and migration of NSCLC cells in vitro. An orthotopic xenograft nude mouse model further affirmed that miR-410 promoted NSCLC cell growth and metastasis in vivo. Moreover, restoring SLC34A2 expression effectively reversed the miR-410-mediated promotion of cell growth, invasion and migration in NSCLC cells. In addition, miR-410^high /SLC34A2^low expression signature frequently existed in NSCLC cells and tumor tissues. MiR-410 significantly increased the expression of DVL2 and β-catenin protein while decreased that of Gsk3β protein of Wnt/β-catenin signaling pathway, while SLC34A2 partly blocked the effects of miR-410 on those protein expressions. Hence, our data for the first time delineated that unusual expression of SLC34A2 was modulated by miR-410, and miR-410 might positivelycontribute to the tumorigenesis and development of NSCLC by down-regulating SLC34A2 and activating Wnt/β-catenin signaling pathway. MiR-410 might be a new potential therapeutic target for NSCLC.

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.

The effects and mechanisms of SLC34A2 on tumorigenicity in human non-small cell lung cancer stem cells

A novel paradigm in tumor biology suggests that non-small cell lung cancer (NSCLC) growth is driven by lung cancer stem cell-like cells (LCSCs), but molecular mechanisms regulating tumorigenic and self-renewal potential of LCSCs are still unclear. Here, we aim to investigate biological function of SLC34A2 in regulating tumorigenicity of LCSCs and its underlying mechanisms. Our findings testified that CD166(+) cells which were derived from fresh primary NSCLC samples displayed stem cell-like features. Fluorescence-activated cell sorting (FACS) analysis showed the presence of a variable fraction of CD166 cells in 15 out of 15 NSCLC samples. Significantly, CD166(+) LCSCs from primary NSCLC tumors expressed high level of SLC34A2 which was required for CD166(+) LCSCs tumorigenic and self-renewal potential. In NSCLC patient cohort, increased SLC34A2 expression correlated with histology, which suggests a potential role of SLC34A2 in CD166(+) LCSCs. Furthermore, Wnt/β-catenin pathway and Bmi1 were found necessary for tumorigenicity and self-renewal capacity of CD166(+) LCSCs by a series in vitro and in vivo experiments. Then, our study indicated that SLC34A2 regulated Bmi1 to promote tumorigenic and self-renewal potential of CD166(+) LCSCs through Wnt/β-catenin pathway. In this study, the characterization of molecular basis of SLC34A2 in CD166(+) LCSCs not only allows for better understanding of the mechanisms regulating tumorigenicity of this specific population of NSCLC cells but also provides insight into the gradual improvement of more effective cancer therapies against this disease.

Enhanced SLC34A2 in breast cancer stem cell-like cells induces chemotherapeutic resistance to doxorubicin via SLC34A2-Bmi1-ABCC5 signaling

Even though early detection methods and treatment options are greatly improved, chemoresistance is still a tremendous challenge for breast cancer therapy. Breast cancer stem cells (BCSCs) represent a subpopulation that is central to chemoresistance. We aim to investigate the relationship between SLC34A2 and chemoresistance in BCSCs and identify the underlying mechanisms by which SLC34A2 regulates chemoresistance in BCSCs. Fluorescence Activated Cell Sorting (FACS) analysis showed the presence of a variable fraction of CD44(+)CD24(-) cells in 25 out of 25 breast cancer samples. We cultured primary breast cancer sample cells and breast cancer cell line cells to induce sphere formation in serum-free medium. Following sorting of CD44(+)CD24(-) cells from spheres, we showed that CD44(+)CD24(-) cells displayed stem cell-like features and were resistant to chemotherapy drug doxorubicin. Significantly, enhanced SLC34A2 expression correlated with chemoresponse and survival of breast cancer patients. We subsequently indicated that increased SLC34A2 expression in BCSCs directly contributed to their chemoresistance by a series of in vitro and in vivo experiments. Furthermore, we demonstrated that SLC34A2 induced chemoresistance in BCSCs via SLC34A2-Bmi1-ABCC5 signaling. Finally, we showed that ABCC5 was a direct transcriptional target of Bmi1 by chromatin immunoprecipitation (ChIP). In conclusion, our work indicated that decreased SLC34A2 expression sensitized BCSCs to doxorubicin via SLC34A2-Bmi1-ABCC5 signaling and shed new light on understanding the mechanism of chemoresistance in BCSCs. This study not only bridges the missing link between stem cell-related transcription factor (Bmi1) and ABC transporter (ABCC5) but also contributes to development of potential therapeutics against breast cancer.

Preclinical Development of an Anti-NaPi2b (SLC34A2) Antibody-Drug Conjugate as a Therapeutic for Non-Small Cell Lung and Ovarian Cancers

PURPOSE

Antibody-drug conjugates (ADC) selectively deliver a cytotoxic drug to cells expressing an accessible antigenic target. Here, we have appended monomethyl auristatin E (MMAE) to an antibody recognizing the SLC34A2 gene product NaPi2b, the type II sodium-phosphate cotransporter, which is highly expressed on tumor surfaces of the lung, ovary, and thyroid as well as on normal lung pneumocytes. This study evaluated its efficacy and safety in preclinical studies.

EXPERIMENTAL DESIGN

The efficacy of anti-NaPi2b ADC was evaluated in mouse ovarian and non-small cell lung cancer (NSCLC) tumor xenograft models, and its toxicity was assessed in rats and cynomolgus monkeys.

RESULTS

We show here that an anti-NaPi2b ADC is effective in mouse ovarian and NSCLC tumor xenograft models and well-tolerated in rats and cynomolgus monkeys at levels in excess of therapeutic doses. Despite high levels of expression in normal lung of non-human primate, the cross-reactive ADC exhibited an acceptable safety profile with a dose-limiting toxicity unrelated to normal tissue target expression. The nonproliferative nature of normal pneumocytes, together with the antiproliferative mechanism of MMAE, likely mitigates the potential liability of this normal tissue expression.

CONCLUSIONS

Overall, our preclinical results suggest that the ADC targeting NaPi2b provides an effective new therapy for the treatment of NSCLC and ovarian cancer and is currently undergoing clinical developments.

Characterization of novel human ovarian cancer-specific transcripts (HOSTs) identified by serial analysis of gene expression

A better understanding of changes in gene expression during ovarian tumorigenesis and the identification of specific tumor markers may lead to novel strategies for diagnosis and therapy for this disease. Using our serial analysis of gene expression (SAGE) data, as well as public SAGE databases that contained a total of 137 SAGE libraries representing a wide variety of normal and neoplastic tissues, we identified five novel SAGE tags specifically expressed in ovarian cancer. Database analysis, cloning and, sequencing of the corresponding expressed sequence tags revealed details about these transcripts that we named human ovarian cancer-specific transcripts (HOSTs). HOST1 was found to be identical to the gene encoding ovarian marker CA125 (MUC16). HOST2 is a novel gene containing multiple copies of retroviral-related sequences without an obvious open reading frame. HOST3 encodes the tight-junction protein claudin-16 (CLDN16). HOST4 encodes a poorly characterized proteoglycan link protein (LP), and HOST5 codes for a type II sodium-dependent phosphate transporter (SLC34A2). Except for MUC16, these genes have not previously been shown to be expressed in ovarian or other cancers. Northern blot analysis confirmed that HOST genes are rarely expressed in normal tissues or nonovarian cancers, but are frequently expressed in ovarian cancer-derived cell lines and primary tumors. Moreover, HOST genes are upregulated in all four major subtypes of ovarian cancer compared to cultivated ovarian surface epithelial cells, as concluded by real-time reverse transcription (RT)-PCR using a panel of microdissected ovarian tumors. The sodium-dependent phosphate transporter (HOST5/SLC34A2) expression was associated with increased differentiation in ovarian serous tumors. While the roles of HOSTs in ovarian malignant transformation remain unclear, we propose that HOSTs may represent alternative targets for diagnosis and therapy and of this deadly disease.