**3.7** *Hcs7* **does not modify apoptosis or mitosis in the acute response to DEN injection**

Other modifiers of DEN-induced hepatocarcinogenesis, such as IL-6 and IKKgamma, have been shown to affect apoptosis and/or mitosis within 72 hours of DEN administration (Maeda et al., 2005; Naugler et al., 2007). To determine whether the tumor susceptibility conferred by the *Hcs7* region affects mitosis or apoptosis rates during this acute response to DEN injection, we collected livers from line 2R8 males one, two, or three days after DEN injection at 12 days of age. Livers were fixed in formalin and stained with H&E. Mitoses and apoptoses were scored based on staining and morphology, under 600× magnification. Two microscopic fields centered on a portal vein and two fields centered on a central vein were scored. Hepatocytes were counted for 10-25 fields per strain and condition (*e.g.*, B6/DEN). Each field represented an equivalent number of hepatocytes per field (~330) in resistant and susceptible mice, independent of DEN treatment (*P* > 0.07 for all comparisons).

Rates of mitosis and apoptosis never differed significantly between B6 and line 2R8, whether or not mice were treated with DEN (*P* > 0.10 for all comparisons; Table 3). These results


indicate that the tumorigenic effect of *Hcs7* does not involve acute changes in the rates of apoptosis or mitosis in response to DEN injection.

Table 3. Mitosis and apoptosis do not differ significantly between line 2R8 and B6 during tumor initiation.
