TGF-beta: a possible autocrine immune regulator

The role of fibroblasts in tumor behavior

The prominent desmoplastic or stromal reaction seen in many invasive carcinomas suggests that stromal cells play a role in cancer pathogenesis. Investigations based on cell typing, using antibodies to cytoskeletal constituents, have revealed that most tumors contain various types of fibroblasts. Stromal cells with myofibroblastic differentiation features are the predominant cell type at the periphery of epithelial tumors. These tumor-activated fibroblasts play a major role in tumor development and spread, affecting the proliferation, differentiation, invasion or regression of cancer cells. This review considers the events inducing the different fibroblastic responses and the role of tumor-activated fibroblasts in both tumor development and anti-cancer treatments.

Elevated plasma transforming growth factor-beta 1 levels in breast cancer patients decrease after surgical removal of the tumor

OBJECTIVE

The authors determined whether untreated breast cancer patients have elevated plasma levels of transforming growth factor-beta 1 (TGF-beta 1).

SUMMARY BACKGROUND DATA

Increased plasma TGF-beta 1 levels recently were found after chemotherapy in patients with advanced breast cancer. However, it currently is unknown whether this elevation in plasma TGF-beta 1 is caused by chemotherapy-induced normal tissue damage or whether it results from the presence of the tumor.

METHODS

An enzyme-linked immunosorbent assay was used to measure plasma TGF-beta 1 levels in 26 newly diagnosed breast cancer patients before and after definitive surgery. Patients were grouped by postoperative tumor status: 1) negative lymph nodes (group 1); 2) positive lymph nodes (group 2); and 3) overt residual disease (group 3). The site of TGF-beta 1 production in the tumors was localized by immunohistochemistry and in situ hybridization.

RESULTS

Plasma TGF-beta 1 levels were elevated preoperatively in 81% of the patients; TGF-beta 2 and TGF-beta 3 were undetectable. The preoperative TGF-beta 1 levels in the three patient groups were similar; however, the postoperative plasma TGF-beta 1 levels differed by disease status. The mean plasma TGF-beta 1 level in group 1 (n = 12) normalized after surgery (19.3 +/- 3.2 vs. 5.5 +/- 1.0 ng/mL, p < 0.001). In contrast, the mean plasma TGF-beta 1 levels remained above normal in both group 2 (n = 9) and group 3 (n = 5) after surgery. Transforming growth factor-beta 1 expression was found to be preferentially increased in the tumor stroma.

CONCLUSIONS

Breast tumors result in increased plasma TGF-beta 1 levels in 81% of patients. After surgical removal of the primary tumor, the plasma TGF-beta 1 level normalizes in the majority of patients; persistently elevated levels correlate with the presence of lymph node metastases or overt residual tumor. These findings suggest that the usefulness of TGF-beta 1 as a potential plasma marker for breast tumors deserves further study.

Transforming growth factor beta 1 null mutation in mice causes excessive inflammatory response and early death

To delineate specific developmental roles of transforming growth factor beta 1 (TGF-beta 1) we have disrupted its cognate gene in mouse embryonic stem cells by homologous recombination to generate TGF-beta 1 null mice. These mice do not produce detectable amounts of either TGF-beta 1 RNA or protein. After normal growth for the first 2 weeks they develop a rapid wasting syndrome and die by 3-4 weeks of age. Pathological examination revealed an excessive inflammatory response with massive infiltration of lymphocytes and macrophages in many organs, but primarily in heart and lungs. Many lesions resembled those found in autoimmune disorders, graft-vs.-host disease, or certain viral diseases. This phenotype suggests a prominent role for TGF-beta 1 in homeostatic regulation of immune cell proliferation and extravasation into tissues.

Basic fibroblast growth factor-induced activation of latent transforming growth factor beta in endothelial cells: regulation of plasminogen activator activity

Exposure of bovine aortic or capillary endothelial cells to basic FGF (bFGF) for 1 h resulted in an approximately sixfold increase in plasminogen activator (PA) activity by 18 h that returned nearly to basal levels by 36 h. We hypothesized that the decrease in PA activity following bFGF stimulation was mediated by transforming growth factor beta (TGF-beta) formed from its inactive precursor. Conditioned medium collected from endothelial cells 36 h after a 1-h exposure to bFGF, but not control medium, inhibited basal levels of PA activity when transferred to confluent monolayers of bovine aortic endothelial cells. Antibody to TGF-beta neutralized the inhibitory activity of this conditioned medium, indicating that the medium contained active TGF-beta. Northern blot analysis and quantitation of acid activatable latent TGF-beta in conditioned medium demonstrated that bFGF exposure did not increase the amount of transcription or secretion of latent TGF-beta by the endothelial cells. Both aprotinin, an inhibitor of plasmin, and anti-urokinase type PA IgG blocked the generation of active TGF-beta in cultures exposed to bFGF. These results demonstrated that plasmin generated by uPA activity is required for the activation of latent TGF-beta in endothelial cell cultures treated with bFGF. Activation of TGF-beta by endothelial cells exposed to bFGF appears to limit both the degree and duration of PA stimulation. Thus, in bFGF-stimulated endothelial cell cultures, PA levels are controlled by a negative feedback loop: PA, whose expression is stimulated by bFGF, contributes to the formation of TGF-beta, which in turn opposes the effects of bFGF by limiting PA synthesis and activity. These studies suggest a role for TGF-beta in reversing the invasive stage of angiogenesis and contributing to the formation of quiescent capillaries.