Transforming growth factor beta-1 (TGFbeta1) regulates cell-matrix and cell-cell adhesion and suppresses malignancy in TGFbeta1-responsive colon cancer cells early in progression. As abnormal adhesion is a hallmark of malignancy, loss of responsiveness to TGFbeta-1 is thought to disrupt cellular adhesion and normal cellular function and to play a critical role in malignant progression. Thus, understanding how TGFbeta1 controls cellular adhesion in responsive cells and, conversely, how unresponsive cells escape TGFbeta1 control may provide new leads for controlling refractory colon cancer. The results of our previous work have enabled us to formulate four new hypotheses about how TGFbeta1 controls cell- matrix and cell-cell adhesion and about how TGFbeta1-unresponsive cells escape TGFbeta1 control. The hypotheses are (1) Protein kinase Calpha (PKCalpha) is an upstream control point in the TGFbeta1 adhesion signal pathway leading to the induction of fibronectin (FN), FN receptor (FN-R), laminin (LM), and LM receptor LM-R) expression. (2) Induction of FN expression is required for the subsequent induction of the intracellular adhesion molecule carcinoembryonic antigen (CEA) and upregulation of intercellular adhesion. (3) Induction of LM expression is required for the subsequent changes in cell shape and adhesion mediated through specific cytoskeletal and focal adhesion proteins and adhesion receptors. (4) Nonfunctioning translation initiation factor eIF-4E or its insufficient expression is a mechanism of escape from TGFbeta1 control.
The Specific Aims, designed to test these hypotheses, respectively, are (1) To determine the role of PKCalpha in controlling the induction of FN/FN-R and LM/LM-R expression. (2) To determine the mechanisms by which FN regulates the induction of CEA expression. (3) To identify the functional role of LM induction in the cellular expression and distribution of cytokeratins, talin, vinculin, pp125fak, and the alpha5 and alpha6 integrins. (4) To establish how eIF-4E restores TGFbeta1 responsiveness in unresponsive cells.
