Differentially Expressed Somatostatin (SST) and Its Receptors (SST1-5) in Sporadic Colorectal Cancer and Normal...

Colorectal cancer (CRC) is one of the most common human malignancies worldwide. The somatotropin-releasing inhibitory factor/somatostatin (SRIF/SST) acts through activation of five membrane receptors (SSTRs, SST1-5). The diagnostic and prognostic role of these peptides in sporadic CRC remains unclear. This study aimed to determine the role of tissue expression of SST and all SSTRs in the pathogenesis, diagnosis, and prognosis of sporadic CRC.

The expression of SST and all SSTRs was assessed in the tissues of CRC patients, control colorectal mucosa and lymph node metastasis from the same patients using real-time quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry (IHC).

Decreased SST (mRNA and peptide) and higher SST2 and SST5 (mRNA and peptide) expression in CRC vs. control was noted. A negative correlation between SST mRNA expression and patient's age in CRC and control groups were observed. IHC study confirmed the coexpression of SSTRs in all tissue groups and significant dependence on the cellular localization. Immunoexpression of SST2 and SST3 showed the most correlations with clinicopathological data in CRC patients. Interestingly, only control tissue showed differences in SST1-5 expression depending on the colon segment.

Reduced SST expression in CRC indicates a weakening in its antitumor effect in this cancer in vivo. Overexpression of SST2 and SST5 in CRC suggests that these receptors play an important role in the pathogenesis of this cancer. Analysis of SST1-5 tissue expression allows for differentiation between the mucinous and nonmucinous CRC subtypes. The coexpression of all SST1-5 and overexpression of not only SST2 and SST5 in CRC may have applications for future therapy based on the SRIF system in sporadic CRC.