A DIFFERENT CYTOCHROME-P450 FORM IS INDUCED IN PRIMARY CULTURES OF RAT HEPATOCYTES

A 49-kDa protein (P49) was discovered in the primary cultures of rat hepatocytes. P49 cross-reacted with the antibodies against purified P450IIC11 [formerly P-450(M-1)]. P49 was located in microsomes and highly induced after plating of isolated hepatocytes on collagen-coated culture dishes. To characterize P49, cDNA clones were screened from a rat liver λgt11 expression library. From sequence analysis of the cloned cDNAs, the amino acid sequence of P49 was deduced, and the protein was identified as a previously uncharacterized form of cytochrome P450. P49 consists of 489 amino acids and shows ≃60% similarity with the members of class IIC subfamily of rat cytochrome P450, such as P450IIC11 and P450IIC12 [formerly P-450(F-1)]. RNA blot analysis indicates that the mRNA translating P49 was induced ≃20- to 30-fold at 70 hr in the primary cultures compared with the liver of adult rats. Induction of P49 was not affected by density of the plated cells and the presence or absence of several hormones, serum, or antibiotics in the culture medium. On the other hand, lower induction of P49 was seen when the hepatocytes were cultured on Matrigel-coated plates. Expression of P49 mRNA was low in the liver of adult rats and was not detectable in the livers of 1- and 2-week-old male and female rats. P49 is an additional form of cytochrome P450, which is induced in the primary culture of rat hepatocytes.