Overexpression Of DARPP-32 In Gastric And Colorectal Adenocarcinoma

DARPP-32 is a phosphoprotein regarded as an essential mediator of the biological effects of dopamine, which plays a central role in the neurobiology of slow synaptic transmission. DARPP-32 is also the only known bifunctional protein that can acts as a PP1 inhibitor or a PKA inhibitor. It orchestrates the degree of phosphorylation in a variety of molecular targets in the cell membrane and cytoplasm. Recent studies have demonstrated that DARPP-32 and t-DARPP were abundantly overexpressed in gastric cancer, which suggested that DARPP-32 may be involved in the signaling pathways that are important for tumorgenesis, but the mechanism remains obscure. To understand the potential role of DARPP-32 in human cancer, additional studies and biological assays are required.Aims: To investigate the expression of DARPP-32 protein in gastric and coiorectal adenocarcinoma tissues and cell lines; To construct DARPP-32 sense and DARPP-32 specific siRNA eukaryotic expression vector.Methods:The expression of DARPP-32 was evaluated by immunohistochemical staining and Western blot. DARPP-32 senseeukaryotic expression vector and specific siRNA vector of DARPP-32 were constructed by DNA recombination technique and siRNA technique.Results : (1) The expression rate of DARPP-32 in gastric adenocarcinoma tissues (92.71%) was significantly higher than that in normal gastric tissues(52.63% , P<0.05).The expression of DARPP-32 had no significant relationship with differentiation, metastasis and invasion of the cancer.(2)Both DARPP-32 and its truncated isoform t-DARPP were overexpressed in gastric adenocarcinoma tissues as compared with adjacent non-carcinomous tissues(r=2.45, P=0.015), and t-DARPP was more frequently seen.(3) Expression of DARPP-32 and t-DARPP could also be detected in human gastric cancer cell lines. The expression of DARPP-32(32KD) was down-regulated in SGC7901 drug-resistant cell strains. (4) DARPP-32 was specifically localized in colorectal epithelium. The expression of DARPP-32 in colorectal adenocarcinoma tissues ( 33/42, 78.57%) was higher than that in normal colon epithelial tissues(3 1/60, 51.67%, P<0.05). There was no significant relationship between the expression of DARPP-32 and the differentiation, metastasis and Dukes' stage of colorectal adenocarcinoma(P>0.05). (5) Both DARPP-32 and its truncated isoform t-DARPP were overexpressed in colorectal adenocarcinoma ( t=2.306, P=0.028), while t-DARPP was more frequently detected.(6)DARPP-32 sense and DARPP-32 specific siRNA eukaryotic expression vector were constructed and identified by DNA sequencing and digestion of restrictive endonuclease successfully.Conclusion : (1) DARPP-32 may be involved in the carcinogenesis of gastric cancer. (2) DARPP-32 and its signalingpathway may be associated with gastric cancer multi-drug resistance. (3)DARPP-32 may play an important role in the regulation of normal colorectal epithelial biology and carcinogenesis. (4)DARPP-32 sense and DARPP-32 specific siRNA expression vector were constructed successfully.