Transforming growth factor-beta1 and regulators of apoptosis

Growth inhibitory function of transforming growth factor-beta1 (TGF-beta1) is abolished in colorectal cancer cells as a consequence of mutations of various downstream signaling agents, such as p53, which fail to respond to TGF-beta1 stimulation. TGF-beta1 could also suppress T-cell-mediated anticancer immunity. We aimed at a comparison between cancer expressions of apoptosis regulators, such as p53, BCL-2-associated X protein (Bax), and B-cell leukemia/lymphoma extra-long protein (Bcl-xL), with TGF-beta1 in malignant and adjacent inflammatory cells in immunohistochemical evaluations of 108 colorectal cancers. Cytoplasm compartment of cancer cells was overloaded with TGF-beta1, and 87% of all cancers were TGF-beta1 positive (94/108). A very strong pattern of staining was detected for TGF-beta1 in cytoplasm of inflammatory cells at tumor margins. TGF-beta1 correlated with Bcl-xL and Bax in all colorectal cancers (P < 0.001, r= 0.473 and P < 0.001, r= 0.435, respectively) and subgroups of different clinicopathological features, especially in deeply invading cancers (pT3+pT4) instead of superficially growing tumors (pT1+pT2). Expression of TGF-beta1 in inflammatory infiltrates correlated with immunoreactivities to Bcl-xL of cancer cells (P= 0.024, r= 0.217). TGF-beta1 did not associate with p53, nor did TGF-beta1 of inflammatory cells correlate with Bax expression in cancer cells. Lack of correlations between TGF-beta1 and p53 proteins could indicate mutations at the TGF-beta1-dependent apoptotic pathway. Dominant positive linkage between TGF-beta1 and Bcl-xL and selective lack of association with Bax suggest TGF-beta1 could support colorectal cancer cell survival. The pattern of correlations seems to confirm a remarkable shift from TGF-beta1-dependent suppression of cancer growth by apoptosis to inhibition of anticancer immunity by TGF-beta1.