Induction of Glutathione S‐Transferase P‐Form in Primary Cultured Rat Hepatocytes by Epidermal Growth Factor and Insulin

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Abstract
The effects of epidermal growth factor (EGF) (10 ng/ml) and insulin (100 nM) on the expression of glutathione S‐transferases (GSTs), especially the GST‐P form (GST 7–7), were examined in primary cultured rat hepatocytes in serum‐free medium. On culture with EGF and insulin, the GST activities towards l‐chloro‐2,4‐dinitrohenzene and l,2‐dichloro‐4‐nitrobenzene were transiently decreased on day 2 to 10% of those of freshly isolated hepatocytes and then increased to 60 to 100% of those of freshly isolated cells on day 4. Western hlot analysis of GSTs revealed that GST‐P, which is not present in freshly isolated hepatocytes, was markedly induced and that GST subimits 3 and 4 of the Mu class also increased after addition of EGF and/or insulin, while the subunits 1 and 2 of the Alpha class disappeared. Northern blot analysis showed that on addition of EGF and insulin the level of GST‐P mRNA was also elevated and expressions of the nuclear oncogenes c‐jun and c‐fos were enhanced. These results suggest that the enhanced expression of GST‐P induced by EGF or insulin in primary cultured rat hepatocytes might he regulated by JUN and FOS proteins.