Elucidating the secretion proteome of human
The most apparent function of the GIT is the digestion of food and uptake of nutrients.The stomach secretes a number of unique enzymes involved in nutrient breakdown including the pepsinogens PGA3, PGA4 and PGC and the lipase LIPF.The pancreatic and duodenal homeobox 1 (PDX1) is a transcription factor that activates insulin transcription and plays a role in beta-cell function and survival.Here, we found the highest expression of PDX1 m RNA and protein in the human duodenum.The analysis showed that 77% of the m RNA molecules in the GIT corresponded to housekeeping genes and only 14% of the m RNA pool represented genes categorized to be tissue-enriched, group-enriched or enhanced involving at least one tissue of the GIT.Thus, most of the transcriptional activity in the GIT relates to proteins with presumed housekeeping functions as they are found in all tissues and cells analyzed.The transcriptome analysis shows that 74% of all human proteins (n=19613) are expressed in at least one region of the GIT.
In more distal regions of the GIT, specific expression of an increasing number of transport-related proteins was found.The four categories of genes with elevated expression in the GIT compared to other organs are shown in Table 1. 165 of the 228 group enriched genes have higher m RNA levels in a group of tissues including more than one GIT tissue. The 12 genes with the highest level of tissue type-specific expression in the GIT.The list of tissue-enriched (n=35) and group-enriched genes (n=228) is well in line with the various functions of the GIT. An analysis of the expression levels of each gene makes it possible to calculate the relative m RNA pool for each of the categories.In addition, the specific proteomes of the salivary gland and the esophagus are presented separately. The distribution of all genes across the five categories based on transcript abundance in GIT as well as in all other tissues.625 genes show some level of elevated expression in the GIT compared to other tissues.
Peptide YY (PYY) expressing cells are primarily found in colon and small intestine.