Fibronectin-mediated hepatocyte shape change reprograms cytochrome p450 2C11 gene expression via an integrin-signaled induction of ribonuclease activity

A major limitation to the use of rat hepatocytes in the study of drug metab olism and toxicity is the rapid loss of CYPs. We demonstrate that the cultu re of rat hepatocytes results in a rapid loss of liver-specific CYP2C11 mRN A and transcripts encoding the general housekeeping gene copper-zinc supero xide dismutase (CuZnSOD) as well as poly(A(+)) mRNA. These losses are accel erated by fibronectin, which has no effect on the transcription of CYP2C11 and CuZnSOD. However, fibronectin, an extracellular matrix protein involved in cell adhesion and spreading, induces ribonuclease (RNase) activity. Fib ronectin also increases hepatocyte diameter and data are presented that cel l spreading is involved in the loss of both CYP2C11 and CuZnSOD mRNAs. The use of functional blocking antibodies demonstrates that fibronectin is oper ating through its alpha(5)beta(1) integrin receptor and genistein, a tyrosi ne kinase inhibitor, prevents hepatocyte spreading, RNase induction, and CY P2C11 mRNA loss. Collectively, the data indicate that hepatocytes in vitro actively promote the extinction of their phenotype via the autocrine effect s of fibronectin rather than the current consensus that they simply lose di fferentiated function, such as CYP2C11 expression, through the absence of e xtracellular matrix proteins. The substrate specificity of the ribonuclease induced is also considered.