A Controversial Tumor Marker:  Is SM22 a Proper Biomarker for Gastric Cancer Cells?

Abstract

SM22, a dominant protein in smooth muscle cells (SMCs), has been widely reported to be abnormally expressed in many solid tumors. However, the expression patterns of SM22 are not consistent in all tumors, not even in the same ones. Whether SM22 should be considered a tumor biomarker is still debated in different laboratories. Herein, we have carried out a systematical investigation to validate SM22 expression in the primary tissues of gastric cancer (GC). Of eight cases, seven samples were found in the elevated expression of SM22 proteins through proteomic analysis. The observation was further verified by the approaches of Western blotting and quantitative RT-PCR. Surprisingly, the results achieved from tissue microarray in 126 GC cases appeared contrary to the proteomic conclusion, in which the highly expressed SM22 was mainly found in smooth muscle layers, blood vessels, and myofibroblasts. This suggested that the increased abundance of SM22 in the cancerous regions was not caused by the presence of the GC cells. Furthermore, the expression of SM22 was measured in different GC cell lines and SMCs with Western blotting and quantitative RT-PCR. The results revealed that SM22 expression in SMCs was dramatically higher than that of the GC cells, which indicates that SM22 is unlikely to be a proper biomarker for GC. Instead, it can be considered a potential indicator for the abnormal developments of smooth muscles, blood vessels, or myofibroblasts triggered by tumorigenesis.

Identification of volatile organic compounds secreted from cancer tissues and bacterial cultures

“…(Table 1). These compounds were recognized by other authors as biomarkers of cancer disease [22][23][24][25][26][27][28][29][30]. However, this chromatogram is very complicated because the cells release a lot of VOCs and some of them are difficult to identify due to frail peaks separation or low detection limit (Fig.…”

“…The activity of bacteria may cause carcinogenic changes in the cells [21]; therefore, a lot of studies have been carried out for characterising substances in breath from patients with lung [22][23][24][25][26], breast [27] and gastric cancer [28][29][30]. It is known that the composition and quantity of VOCs in the exhaled breath from patient with lung cancer varies from healthy volunteers.…”

Proteomics-based identification of a group of apoptosis-related proteins and biomarkers in gastric cancer

“…For example, Li et al reported that SM22, a commonly used tumor marker in the past was actually a sign of neovascularization, and had been identified on the basis of contamination of tumor samples with vascular endothelial cells (37). To avoid this scenario, we took care in the present study, to conform 2-DE results using immunohistochemistry and tissue microarray analysis.…”

Loss of SM22 is a characteristic signature of colon carcinogenesis and its restoration suppresses colon tumorigenicity in vivo and in vitro

“…For example, Qi et al and Ryu et al reported that SM22 was up-regulated in esophageal squamous cell carcinoma and gastric cancer, respectively. [26][27][28] Therefore, systematical investigations are needed to elucidate the expression and function of SM22 in various cancers.…”