Although transforming growth factor (TGF)-beta1 is a potent growth inhibitor of normal epithelial cells including colonocytes, TGF-beta1 has also been implicated as an enhancer of colon cancer metastasis. Decreasing TGF-beta1 protein levels in the metastatic U9 colon cancer cell line by antisense methodology decreased both U9 cell metastasis to the liver and s.c. tumor formation in a nude mouse system, and the tumors that did arise had regained TGF-beta1 expression (F. Huang et al, Cell Growth Differ., 6: 1635-1642, 1995). In addition, in a clinical immunohistochemistry study, colon cancers with elevated TGF-beta1 protein levels were found to be 18 times more likely to recur as distant metastases than colon cancers expressing low TGF-beta1 levels, after resection of the primary tumor (E. Friedman et al, Cancer Epidemiol. Biomark. Prev., 4:549-554, 1995). Because both studies implicated TGF-beta1 in colon cancer metastasis, we wished to know whether a selection bias for TGF-beta1 was maintained in metastatic cells or was only a property of the primary site tumors that were likely to metastasize. TGF-beta1 levels were measured using two different antibodies in paired primary site cancers and their metastases by immunohistochemistry and, in selected cases, by Western blot analysis. In 16 of 21 cases (76%) with antibody G and 23 of 31 cases (74%) with antibody P, higher expression of TGF-beta1 was found in colon cancer cells invading local lymph nodes compared with primary site colon cancer cells, or (2 and 6 cases, respectively) high TGF-beta1 expression in the primary site cancer was maintained in invasive cells. Analysis by Western blotting using both antibodies also demonstrated that higher levels of TGF-beta1 protein were found in metastases compared with the primary site tumor or normal tissue. Additional cases of paired primary site colon cancer, local lymph node metastases, and cancer cells metastasizing to distant sites were examined. In six of eight such cases (75%), TGF-beta1 levels were increased in both invasive cell populations compared with the primary site cancer (five cases), or high levels in the primary site cancer were maintained in the metastatic cells (one case). These data suggest that TGF-beta1 plays a role in promoting colon cancer metastasis throughout the metastatic process in roughly 75% of cases. TGF-beta1 may increase metastasis by paracrine mechanisms, such as suppression of local immune response or increased angiogenesis, as was seen with the U9 cell line. In those cancers with nonmutated TGF-beta receptors and nonmutated smad proteins like U9 cells, TGF-beta1 could also act in an autocrine manner to increase invasion by increasing cell motility (Hsu et al., Cell Growth Differ., 5: 267-275, 1994).

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