Study On The Relationship Between Dysregulated Expression Of Protein And Cells Proportion In Cancer Peripheral Blood

Background: Cancer screening and early detection are the most promising methods to greatly improve the survival rate of cancer patients.Blood-based biopsy tests for identifying protein biomarkers hold a great promise for early diagnosis of cancer.However,it has been observed that DNA methylation and differential blood m RNAs changes in the peripheral whole blood of cancer patients and inflammatory disease patients are predominantly determined by the increase of myeloid cells and the decrease of lymphoid cells under the disease conditions.Thus,the ratio shifts of peripheral blood cells,instead of the secretion of cancer cells,might explain the serum or plasm concentration changes of many protein biomarkers in cancer patients versus normal controls,so that these proteins were difficult to differentiate cancer patients from inflammatory patients.Methods: Firstly,we use the Cell Mix package to estimate the proportion of myeloid and lymphoid cells for each PDAC sample and healthy control sample in the two pancreatic ductal adenocarcinoma(PDAC)peripheral whole blood gene expression profiles.Then,from literature in Pub Med database,serum and plasm differentially expressed proteins in cancer patients versus normal controls were collected,and their expression patterns were examined in the two microarray gene expression profiles of myeloid cells and lymphoid cells,respectively.Finally,for validating the dysregulation directions of APOA2 and THBS1 in disease patients versus healthy controls,their concentrations were measured in the serum samples of 30 PDAC patients,30 pancreatitis patients and 30 healthy volunteers using the enzyme-linked immunosorbent assay(ELISA).Results: The proportion of myeloid cells in PDAC peripheral whole blood was significantly higher than that in normal peripheral whole blood,while the proportion of lymphoid cells was significantly lower than that in normal peripheral whole blood(Student’s t test,P = 0.016).Furthermore,the genes encoding 15 of the 46 serum and plasma differentially expressed proteins in PDAC versus normal controls were found to be significantly dysregulated in myeloid cells versus lymphoid cells and 13 of these 15 biomarker genes,except APOA2 and THBS1,were dysregulated to the same directions as in PDAC patients versus normal controls(binomial test,P = 3.7E-03).Comparably,among 54 serum and plasm differentially expressed proteins in other nine types of cancer(colorectal cancer,gastric cancer,hepatocellular carcinoma,lung cancer,ovarian cancer,squamous cell carcinoma breast cancer,clear renal cell carcinoma,and gallbladder cancer)patients versus normal controls,the genes expressing 18 proteins were significantly dysregulated in myeloid cells versus lymphoid cells,of which 14 share the same dysregulation directions as in cancers versus normal controls(binomial test,P =1.54E-02).Experimentally,we confirmed that APOA2 and THBS1 were significantly up-regulated in PDAC patients versus normal controls(Student’s t test,P < 0.05)as their coding genes in myeloid cells versus lymphoid cells,while there were no significant differences between PDAC patients and pancreatitis patients.Conclusions: Many serum and plasma differentially expressed proteins in cancers versus normal controls share the same dysregulation directions as their encoding genes in myeloid versus lymphoid cells,which mean that the observed changes of many protein biomarkers determined by the ratio shifts of peripheral blood cells under the disease conditions.Therefore,it is important to consider the population shift of peripheral blood cells and to include inflammatory controls when developing blood-based cancer specific biomarkers.