Elevated c-Src protein expression is an early event in colonic neoplasia

Abstract

The molecular events regulating the development and progression of colonic neoplasia are currently being delineated. Recent studies have implicated c-Src protein kinase activation as an early event in the malignant transformation of colonic epithelial cells. However, increased c-Src activity has also been reported in colon carcinomas as well as in metastatic hepatic and extrahepatic colon carcinomas. To further investigate the potential role of c-Src in the progression of colonic neoplasia, we analyzed c-Src levels by immunohistochemistry in 27 colorectal resection specimens. Mouse monoclonal antibody to c-Src protein was applied to 3-micron sections from formalin-fixed, paraffin-embedded tissues using the avidin-biotin-peroxidase method. The combination of adenomatous (AD) and adjacent carcinomatous mucosa (CA) specimens were present in 20 of 27 patients. In 15 cases, synchronous metastatic (MT) lesions were available for evaluation. Strong c-Src expression was evident in 95% of AD (n = 20), in contradistinction to 32% of MT (n = 19) and 14% of CA (n = 22). Weak-to-moderate c-Src expression was seen in adjacent normal colonic mucosa (NM) in 96% of cases. Signed rank test univariate analysis revealed a statistically significant difference in c-Src expression between NM/AD (p = 0.0001), NM/CA (p = 0.0001), NM/MT (p = 0.0006), AD/CA (p = 0.0001), and AD/MT (p = 0.0002). No significant correlation between levels of c-Src expression and patient survival, tumor size, histologic grade, or tumor configuration was observed using the Cox's Regression Model. Similar results were obtained by analysis of c-Src protein levels and c-Src kinase activity as measured by Western blot and in vitro kinase assays of representative cases. Our results indicate that: (a) elevated c-Src expression is an important early event during colorectal carcinogenesis; (b) its activation may be involved in tumor progression in a subset of colonic carcinomas; and (c) additional molecular events are necessary for invasion to occur.