Expression profiling and intracellular localization studies of the novel Proline-, Histidine-, and Glycine-rich protein 1 suggest an essential role in gastro-intestinal epithelium and a potential clinical application in colorectal cancer diagnostics.

Satu Oltedal,Bjørnar Gilje,Kjersti Tjensvoll,Reino Heikkilä,Emiel A M Janssen,Ivar Skaland,Jodi Maple-Grødem,Rune Smaaland,Oddmund Nordgård

doi:10.1186/s12876-018-0752-8

Abstract

BackgroundThe primary function of the intestines is the absorption of water and nutrients. Although our knowledge about these processes on the cellular level is extensive, a number of important intracellular elements remain unknown. Here, we characterize the novel proline-, histidine-, glycine-rich 1 (PHGR1) mRNA and protein on the molecular level and propose a functional role of the PHGR1 protein in the intestinal and gastric epithelium.MethodsPHGR1 mRNA and protein expression in human tissues and cell lines were characterized by quantitative RT-PCR, in situ hybridization, Northern blotting, Western blotting, and immunohistochemistry. Glycosylation was assessed by a chemical deglycosylation assay, whereas intracellular localization was studied by immunofluorescent staining of cell line cells. PHGR1 mRNA levels in HT29 cells was reduced by RNA interference and the resulting global changes in gene expression assessed by microarray hybridization.ResultsPHGR1 mRNA and protein were found to be expressed specifically in epithelial cells of intestinal mucosa, with the highest expression in the most mature and differentiated cells. PHGR1 protein was found to be glycosylated and to localize to both the cytoplasm and nucleus. Transcript profiling and gene ontology analysis of HT29 cells subjected to PHGR1 knockdown suggested a functional relationship with transport and metabolic processes. Examination of PHGR1 mRNA and protein levels in lymph nodes with known colorectal cancer metastases indicated that they may serve as biomarkers for detection of such metastases.ConclusionsFunctional analyses of the novel PHGR1 mRNA and protein suggest an essential role in gastrointestinal epithelium and a clinical application in detection of colorectal cancer lymph node metastases.

Highlights

The primary function of the intestines is the absorption of water and nutrients
Among the mRNAs apparently only expressed in normal and neoplastic colon tissues were several well-known colonic differentiation markers and a novel mRNA later denoted as proline, histidine, glycine-rich protein 1 (PHGR1)
Transcript profile in response to PHGR1 downregulation To elucidate the functional pathways related to PHGR1 expression, we investigated the global transcriptional effects of PHGR1 knockdown in HT29 colon cancer cells

Summary

Introduction

The primary function of the intestines is the absorption of water and nutrients. Other primary functions of the mucosa are absorption, secretion, and maintaining symbiosis with the intestinal microbiota [1]. The intestinal mucosa is covered by a single cell layer consisting primarily of four cell types [1, 2]. The most abundant cells are the absorptive enterocytes; goblet cells and enteroendocrine cells secrete mucus and various hormones; and Paneth cells secrete bactericidal proteins, such as lysozyme and defensins. Goblet cells, and enteroendocrine cells cover the villi of the small intestine and the luminal surface of the large intestine. Paneth cells and immature enterocytes, goblet, and enteroendocrine cells reside in the basal parts of the crypts, which is a niche of proliferation and cell differentiation. The bottom of each crypt harbors stem cells that give rise to all of the cell types described above [2]

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