Pdx1, a homeodomain transcription factor required for pancreas development, maps to rat chromosome 12

PDX-1: A Promising Therapeutic Target to Reverse Diabetes

The pancreatic duodenum homeobox-1 (PDX-1) is a transcription factor encoded by a Hox-like homeodomain gene that plays a crucial role in pancreatic development, β-cell differentiation, and the maintenance of mature β-cell functions. Research on the relationship between PDX-1 and diabetes has gained much attention because of the increasing prevalence of diabetes melitus (DM). Recent studies have shown that the overexpression of PDX-1 regulates pancreatic development and promotes β-cell differentiation and insulin secretion. It also plays a vital role in cell remodeling, gene editing, and drug development. Conversely, the absence of PDX-1 increases susceptibility to DM. Therefore, in this review, we summarized the role of PDX-1 in pancreatic development and the pathogenesis of DM. A better understanding of PDX-1 will deepen our knowledge of the pathophysiology of DM and provide a scientific basis for exploring PDX-1 as a potential target for treating diabetes.

Culturing and transcriptome profiling of progenitor-like colonies derived from adult mouse pancreas

Background

Transplantation of insulin-producing cells is considered an important diabetes therapy. Many research studies have shown that insulin-producing cells can be derived from the in-vitro cultured pancreatic colonies with self-renewal ability and multilineage potential. Even though these progenitor-like colonies have been prepared from adult pancreas cells, the efficient culture method is hardly established and regulation of the colonies is rarely known. We confirmed previously that single cells acquired from adult mouse pancreas could form cyst-like colonies in a 3D semi-solid system containing Matrigel and methylcellulose. These colonies could be passaged continuously without losing progenitor-like capacity. In the previous culturing system, however, conditioned medium from murine embryonic-stem-cell-derived pancreatic-like cells was used. This unregulated ingredient may reduce repeatability and affect following study. Thus, a new culturing system with certain components needs to be developed.

Methods

Single cell suspension was acquired from adult mouse pancreas and cultured in a Matrigel-based 3D system with epidermal growth factor, Nicotinamide, B27, and Noggin to form ring colonies. Serial-passage assay was performed to evaluate self-renewal ability. Real-time polymerase chain reaction and immunostaining were used to detect the expression of progenitor-related genes. A 2D differentiation method was used to testify the multilineage potency of the colonies. High-throughput sequencing (HTS) of the colonies was performed to profile the differentially expressed genes.

Results

We developed a 3D culturing system deprived of conditioned medium to propagate those colonies with high proliferative efficiency. HTS of the transcriptome of mRNAs, microRNAs (miRNAs) and long noncoding RNAs (lncRNAs) showed differentially expressed genes compared to the whole pancreas (as control). In mRNAs, several surface marker genes were identified in the colonies. Moreover in noncoding RNAs, miR-21a, miR-31 and miR-155 were upregulated and miR-217, miR-802 and miR-375 were downregulated in colonies along with a number of other miRNAs and lncRNAs.

Conclusions

Our results offer an efficient culture system for pancreatic progenitor-like colonies and HTS of the colonies serves as a target resource for following study of in-vitro cultured pancreatic progenitors. These findings should also contribute to our understanding of the transcriptional regulation of these progenitor-like colonies and the mechanisms behind their functions.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0626-y) contains supplementary material, which is available to authorized users.

PDX-1: demonstration of oncogenic properties in pancreatic cancer

BACKGROUND

Pancreatic-duodenal homeobox 1 (PDX-1) is a transcription factor that regulates embryologic pancreas development and insulin expression in the adult islet; however, it is overexpressed in many types of cancer, including pancreatic cancer. The purpose of this study was to investigate the role of PDX-1 in tumorigenesis in human cells.

METHODS

In vitro cell proliferation, invasion, and transformation were performed in human embryonic kidney cell line (HEK 293), pancreatic cancer cell line MIA PaCa2, and human pancreatic ductal epithelial (HPDE) cells transiently or stably expressing PDX-1 or green fluorescent protein (GFP) PDX-1, with or without cotransfection of PDX-1 short hairpin RNA (shRNA). In vivo tumor formation was carried out in severe combined immunodeficiency (SCID) mice with subcutaneous injection of HEK 293 and MIA PaCa2 stably transfected cells. Cell cycle was analyzed by Western blot or immunostaining. Microarray of RNA from pancreatic adenocarcinoma cells with and without PDX-1 shRNA was performed and analyzed.

RESULTS

Transient and stable expressing PDX-1 significantly increased cell proliferation and invasion in HEK 293, human pancreatic ductal epithelial (HPDE), and MIA PaCa2 cells versus controls (P < .05), human PDX-1 shRNA reversed these effects. Expression of PDX-1 significantly increased colony formation in HEK 293, HPDE, and MIA PaCa2 cells versus controls in vitro (P < .05). PDX-1 promoted HEK 293 and MIA PaCa2 tumor formation in SCID mice as compared with that of control (P < .05). PDX-1 overexpression disrupted cell cycles proteins. PDX-1 expression was confirmed by Western blot and tracked by viewing of GFP-PDX-1 expression. Microarray data support an oncogenic role of PDX-1 in pancreas cancer cells.

CONCLUSIONS

PDX-1 induced increased cell proliferation, invasion, and colony formation in vitro, and resulted in markedly increased HEK 293 and MIA PaCa2 tumor formation in SCID mice. These data suggest that PDX-1 is a potential oncogene that regulates tumorigenesis.

In vitro pancreas duodenal homeobox-1 enhances the differentiation of pancreatic ductal epithelial cells into insulin-producing cells

AIM: To observe whether pancreatic and duodenal homeobox factor-1 enhances the differentiation of pancreatic ductal epithelial cells into insulin-producing cells in vitro.

METHODS: Rat pancreatic tissue was submitted to digestion by collagenase, ductal epithelial cells were separated by density gradient centrifugation and then cultured in RPMI1640 medium with 10% fetal bovine serum. After 3-5 passages, the cells were incubated in a six-well plate for 24 h before transfection of recombination plasmid XlHbox8VP16. Lightcycler quantitative real-time RT-PCR was used to detect the expression of PDX-1 and insulin mRNA in pancreatic epithelial cells. The expression of PDX-1 and insulin protein was analyzed by Western blotting. Insulin secretion was detected by radioimmunoassay. Insulin-producing cells were detected by dithizone-staining.

RESULTS: XlHbox8 mRNA was expressed in pancreatic ductal epithelial cells. PDX-1 and insulin mRNA as well as PDX-1 and insulin protein were significantly increased in the transfected group. The production and insulin secretion of insulin-producing cells differentiated from pancreatic ductal epithelial cells were higher than those of the untransfected cells in vitro with a significant difference (1.32 ± 0.43 vs 3.48 ± 0.81, P < 0.01 at 5.6 mmol/L; 4.86 ± 1.15 vs 10.25 ± 1.32, P < 0.01 at 16.7 mmol/L).

CONCLUSION: PDX-1 can differentiate rat pancreatic ductal epithelial cells into insulin-producing cells in vitro. In vitro PDX-1 transfection is a valuable strategy for increasing the source of insulin-producing cells.

PDX-1 and the pancreas

Many transcription factors are critical for ensuring proper embryonic development of the endocrine pancreas and normal islet function. The transcription factor pancreatic duodenal homeobox 1 (PDX-1) is uniformly expressed in early pancreatic buds of embryos as well as the beta and delta cells of the islets of Langerhans. PDX-1 has also been found in dispersed endocrine cells of the duodenum in adults and plays a key role in pancreas formation. It has been reported that null mutation of PDX-1 in mice results in a failure of the pancreatic bud to expand; thus, the mice die 2-3 days after birth from hyperglycemia and dehydration. Heterozygous PDX-1 mice developed a pancreas but were diabetic. It has been shown that PDX-1 is required for maintaining the pancreatic islet functions by activating gene transcriptions including insulin, somatostatin (SST), islet amyloid polypeptide, glucose transporter type 2, and glucokinase. PDX-1 serves a dual role in pancreatic development. It initially contributes to pancreatic formation during embryogenesis and subsequently regulates the pancreatic islet cell physiology in mature islet cells. Understanding the underlying molecular mechanisms of pancreas formation, especially the function of PDX-1, may contribute to the enhanced treatment and prevention of debilitating diseases such as diabetes, insulinomas, and pancreatic carcinomas.

Regulation of pdx-1 gene expression

The homeodomain-containing transcription factor pancreatic duodenal homeobox 1 (PDX-1) plays a key role in pancreas development and in beta-cell function. Upstream sequences of the gene up to about -6 kb show islet-specific activity in transgenic mice. Attempts to identify functional regulatory elements involved in the controlled expression of the pdx-1 gene led to the identification of distinct distal beta-cell-specific enhancers in human and rat genes. Three additional sequences, conserved between the mouse and the human 5'-flanking regions, two of which are also found in the chicken gene, conferred beta-cell-specific expression on a reporter gene, albeit to different extents. A number of transcription factors binding to and modulating the transcriptional activity of the regulatory elements were identified, such as hepatocyte nuclear factor (HNF)-3beta, HNF-1alpha, SP1/3, and, interestingly, PDX-1 itself. A fourth conserved region was localized to the proximal promoter around an E-box motif and was found to bind members of the upstream stimulatory factor (USF) family of transcription factors. We postulate that disruption of pdx-1 cis-acting regulatory sequences and/or mutations or functional impairment of transcription factors controlling the expression of the gene can lead to diabetes.