Stain-Free technology as a normalization tool in Western blot analysis

Gross Cystic Disease Fluid Protein-15(GCDFP-15)/Prolactin-Inducible Protein (PIP) as Functional Salivary Biomarker for Primary Sjögren's Syndrome

BACKGROUND

Gross cystic disease fluid protein-15(GCDFP-15)/prolactin-inducible protein (PIP) is a secretory acinar glycoprotein of 14 KDa which we have recently described as significantly lower in salivary samples of patients with primary Sjögren's syndrome (pSS) in comparison to healthy volunteers by proteomic analysis.

AIMS OF THE STUDY

(1) to validate our previous data on the decrease of GCDFP-15/PIP protein in a larger number of subjects with pSS (2) to integrate the proteomic results with complementary immunoassays in order better clarify the pathophysiological relevance of GCDFP-15/PIP in pSS exocrinopathy (3) to assess both the glandular expression of the GCDFP-15/PIP and the levels of glandular GCDFP-15/PIP mRNA in the patients' minor salivary gland (MSG) biopsies in order to verify whether the observed reduction of GCDFP-15/PIP in saliva may be related to a decrease in the protein production.

PATIENTS AND METHODS

A total of 123 salivary samples from patients affected by pSS, no-SS sicca syndrome and sex- age-matched healthy volunteers were analyzed by different proteomic techniques (SELDI-TOF-MS, 2DE, MALDI-TOF-MS). The expression of GCDFP-15/PIP was then validated by western blot analysis. Real Time PCR and immunohistochemistry for GCDFP-15/PIP in the minor salivary glands (MSG) biopsies were then carried out.

RESULTS

By using complementary proteomic analysis we found that a putative peak of 16547 m/z was among the best independent biomarkers for pSS able to discriminate between patients and healthy controls with a sensitivity of 96 % and a specificity of 70%, with a global cross validated error of 29%. We identified the peak as the GCDFP-15/PIP protein and verified that the intensity of GCDFP-15/PIP was significantly lower in pSS patients when compared to both no-SS sicca subjects and healthy controls (p<0.0001). GCDFP-15/PIP expression also correlated with both the salivary flow rate (r=0.312, p=0.023) and MSG biopsies focus score (r=-0.377, p=0.04). Finally, immunohistochemistry confirmed that GCDFP-15/PIP staining was faint in mucus acini and Real Time PCR showed that GCDFP-15/PIP mRNA was significantly lower in pSS patients when compared to both no-SS sicca subjects and healthy controls (p=0.023) thus supporting the hypothesis that the observed reduction of GCDFP-15/PIP in pSS saliva may be related to a decrease in the protein production.

CONCLUSION

In this study by different complementary-omic techniques we confirmed the potential role of GCDFP-15/PIP as a novel biomarker for pSS. This finding might also be functionally important as GCDFP-15/PIP has previously been shown to bind to Aquaporin 5 (AQP5), a salivary gland water channel, critical to saliva formation that is known to be downregulated in pSS. It is likely that exploring the GCDFP-15/PIP/AQP5 axis will help better understand the mechanism of salivary gland dysfunction in pSS.

miR-150, p53 protein and relevant miRNAs consist of a regulatory network in NSCLC tumorigenesis

microRNAs (miRNAs) are a class of non-coding small RNAs that act as negative regulators of gene expression by binding to the 3'-untranslated region (3'-UTR) of target mRNAs. Tumor protein p53, a transcriptional factor, plays an important role in the progression of tumorigenesis. miR-150 was the only miRNA predicted to target 3'-UTR of p53 by Targetscan. In order to investigate the function of miR-150, p53 and relevant miRNAs in non-small cell lung cancer (NSCLC), we constructed two expression vectors of p53 (pcDNA3.1-p53 and pcDNA3.1-p53-3'-UTR) and two report vectors (pGL3-p53-3'-UTR and pGL3-p53-3'-mUTR). The activity of luciferase transfected with miR-150 mimics was lower by 30% when compared to that of the miRNA-negative control (miRNA-NC). Moreover, the p53 protein was downregulated by at least 50% when miR-150 mimics were cotransfected with pcDNA3.1-p53-3'-UTR when compared to miRNA-NC. We also determined the expression of miR-150 and p53 in NSCLC patient tissue samples. The expression of miR-150 in T2 stage tissue samples was higher than that in T1 stage tissue samples. The corresponding target gene p53 was correlated with miR-150 expression. In the present study, we further analyzed the cell cycle distribution. The cells transfected with pcDNA3.1-p53 were significantly arrested in the G1 phase when compared to the control cells. When miR-150 mimics were cotransfected with pcDNA3.1-p53-3'-UTR, the percentage of cells in the G1 phase was significantly lower by 4% when compared to miRNA-NC. To identify miRNAs that are regulated by the p53 protein, qRT-PCR was performed after pcDNA3.1-p53 transfection. miR-34a, miR-184, miR-181a and miR-148 were upregulated significantly. However, there was no distinct difference in the expression of miR-10a, miR-182 and miR-34c. Our results showed that miR-150 targets the 3'-UTR of p53, and p53 protein promotes the expression of miRNAs which affect cell cycle progression. These findings suggest that miR-150, p53 protein and relevant miRNAs are members of a regulatory network in NSCLC tumorigenesis.

An old method facing a new challenge: re-visiting housekeeping proteins as internal reference control for neuroscience research

The study of specific target protein expression is often performed by western blotting, a commonly used method to measure the protein expression in neuroscience research by specific antibodies. Housekeeping proteins are used as an internal control for protein loading as well as reference in the western blotting analysis. This practice is based on the belief that such housekeeping genes are considered to be ubiquitously and constitutively expressed in every tissue and produce the minimal essential transcripts necessary for normal cellular function. The most commonly used housekeeping proteins are β-actin, β-tubulin, and glyceraldehyde 3-phosphate dehydrogenase (GAPDH). However, recent studies have shown significant variation in some housekeeping genes both at the mRNA and protein levels in various neuropathological events, such as spinal cord injury and Alzheimer's diseases. Changes of housekeeping genes are also induced by non-neuronal diseases in various tissues. Therefore, these discoveries raise a potential concern regarding whether using a housekeeping protein as an internal standard for target protein analysis is an appropriate practice. This minireview will focus on (I) the effects of neuronal and non-neuronal diseases, experimental condition, and tissue-specific roles on alteration of housekeeping genes, and (II) alternative internal standards for gene and protein expression analysis.