Cell-type specificity of β-actin expression and its clinicopathological correlation in gastric adenocarcinoma

To investigate cell type specific distribution of β-actin expression in gastric adenocarcinoma and its correlation with clinicopathological parameters.

β-actin is a housekeeping gene, frequently used as loading control, but, differentially expresses in cancer. In gastric cancer, an overall increased expression of β-actin has been reported using tissue disruptive techniques. At present, no histological data is available to indicate its cell type-specific expression and distribution pattern. In the present study, we analyzed β-actin expression and distribution in paired normal and tumor tissue samples of gastric adenocarcinoma patients using immunohistochemistry (IHC), a tissue non-disruptive technique as well as tissue disruptive techniques like reverse transcriptase-polymerase chain reaction (RT-PCR) and western blotting. Correlation of β-actin level with clinicopathological parameters was done using univariate analysis.

The results of this study showed significant overexpression, at both mRNA and protein level in tumor tissues as confirmed by RT-PCR (1.47 ± 0.13 vs 2.36 ± 0.16; P < 0.001) and western blotting (1.92 ± 0.26 vs 2.88 ± 0.32; P < 0.01). IHC revealed that β-actin expression is majorly distributed between epithelial and inflammatory cells of the tissues. Inflammatory cells showed a significantly higher expression compared to epithelial cells in normal (2.46 ± 0.13 vs 5.92 ± 0.23, P < 0.001), as well as, in tumor tissues (2.79 ± 0.24 vs 6.71 ± 0.14, P < 0.001). Further, comparison of immunostaining between normal and tumor tissues revealed that both epithelial and inflammatory cells overexpress β-actin in tumor tissues, however, significant difference was observed only in inflammatory cells (5.92 ± 0.23 vs 6.71 ± 0.14, P < 0.01). Moreover, combined expression in epithelial and inflammatory cells also showed significant increase (4.19 ± 0.15 vs 4.75 ± 0.14, P < 0.05) in tumor tissues. In addition, univariate analysis showed a positive correlation of β-actin level of inflammatory cells with tumor grade (P < 0.05) while epithelial cells exhibited negative correlation (P > 0.05).

In gastric cancer, β-actin showed an overall higher expression predominantly contributed by inflammatory or tumor infiltrating immune cells of the tissue microenvironment and correlates with tumor grade.