Cholesterol 7 ␣ -hydroxylase, a rate-limiting enzyme for bile acid synthesis, has been implicated in genetic susceptibility to atherosclerosis. The gene, CYP7A1 , encoding a protein with this activity, is expressed normally only in hepatocytes and is highly regulated. Our cyp7A1 gene knockout mouse colony, as young adults on a chow diet, is hypercholesterolemic. These mice were characterized extensively to understand how cyp7A1 affects lipid and bile acid homeostasis in different tissue compartments and whether gender plays a modifying role. Both male and female cyp7A1-deficient mice had decreased hepatic LDL receptors, unchanged hepatic cholesterol synthesis, increased intestinal cholesterol synthesis and bile acid transporters, and decreased fecal bile acids but increased fecal sterols. In females, cyp7A1 deficiency also caused changes in hepatic fatty acid metabolism, decreased hepatic canalicular bile acid transporter, Bsep, and gallbladder bile composition altered to a lithogenic profile. Taken together, the data suggest that cyp7A1 deficiency results in a proatherogenic phenotype in both genders and leads to a prolithogenic phenotype in females.

Experiments undertaken to investigate the binding of epidermal growth factor by hepatocyte nuclei showed that: (a) isolated nuclei from both normal and regenerating rat liver are capable of binding 125I-epidermal growth factor, (b) the nuclear epidermal growth factor-binding protein is similar in molecular weight to the plasma membrane epidermal growth factor receptor, (c) monoclonal antibodies produced against the plasma membrane epidermal growth factor receptor recognize the nuclear epidermal growth factor receptor and (d) the nuclear receptor has an affinity for epidermal growth factor comparable to that of the plasma membrane receptor, but fewer (approximately 10%) nuclear receptors are available per protein unit compared with the plasma membrane.

Background: Proteases facilitate several steps in cancer progression. To identify proteases most suitable for drug targeting, actual enzyme activity and not messenger RNA levels or immunoassay of protein is the ideal assay readout. Materials and Methods: An automated microtiter plate assay format was modified to allow detection of all four major classes of proteases in tissue samples. Fifteen sets of colorectal carcinoma biopsies representing primary tumor, adjacent normal colon, and liver metastases were screened for protease activity. Results: The major proteases detected were matrix metalloproteases (MMP9, MMP2, and MMP1), cathepsin B, cathepsin D, and the mast cell serine proteases, tryptase and chymase. Matrix metalloproteases were expressed at higher levels in the primary tumor than in adjacent normal tissue. The mast cell proteases, in contrast, were at very high levels in adjacent normal tissue, and not detectable in the metastases. Cathepsin B activity was significantly higher in the primary tumor, and highest in the

Cholesterol 7␣-hydroxylase is a rate-limiting enzyme in bile acid synthesis, a major pathway for cholesterol catabolism. It plays a crucial role in postnatal development and survival. In an adult liver, its activity and messenger RNA (mRNA) are heterogeneously distributed with concentration in the pericentral area. We defined how the pattern of cholesterol 7␣-hydroxylase mRNA evolves during rat liver development, correlated this with its total liver mRNA levels, and determined when its heterogeneous pattern of expression is established. Cholesterol 7␣-hydroxylase mRNA was undetectable in 18-day-old fetal livers by Northern blot. It was increased markedly in newborns with a homogeneous liver lobular distribution as determined by in situ hybridization. At postnatal day four, mRNA levels were markedly decreased with concomitant appearance of a lobular gradient: mRNA was detected only in a few hepatocytes located around efferent venules. At 22 days, the time of highest mRNA expression, a marked extension of the gradient towards the periportal area was observed, indicating that the increase in total liver cholesterol 7␣-hydroxylase mRNA level was a result of recruitment of hepatocytes upstream from the central vein area. By 28 days, the adult pattern was observed. Thus, expression of cholesterol 7␣-hydroxylase mRNA is tightly regulated during rat liver development, both temporally and spatially supporting its critical role in normal postnatal development.(HEPATOLOGY 1998;28:1064-1072.)Bile acids play a key role in absorption of lipids, including fat-soluble vitamins. Bile acid synthesis represents the major regulated pathway for catabolism and excretion of cholesterol in mammals. The hepatospecific enzyme cholesterol 7␣-hydroxylase (C7␣H; EC 1.14.13.17; CYP7A) catalyzes a rate-limiting step in this important process. [2][3][4] Its activity is tightly regulated in vivo by a number of different effectors acting predominantly at the transcriptional level. C7␣H is modulated by hormones, including thyroxin, glucocorticoids, and insulin 5-7 ; and by dietary factors. [8][9][10] It is regulated in a negative feedback manner by hydrophobic bile acids returning to the liver via the enterohepatic circulation. 11-13 It exhibits a diurnal rhythm, with maximum activity in the dark phase and minimum during the light phase in rats. [13][14][15] The expression of C7␣H in adult rats is tightly regulated spatially along the liver cell plate; the enzymatic activity 16 and mRNA level 17,18 are not distributed uniformly among parenchymal cells; rather, C7␣H is predominantly found in a subgroup of hepatocytes localized around the central vein.Liver cell heterogeneity is considered to be a major determinant for proper execution and regulation of most liver functions. 19,20 It reflects differentiation of hepatocytes within the liver plate, which is established during development. In most cases, it is regulated at the transcriptional level. The role of liver cell heterogeneity in the developmental regulation of bile acid synthesis is unknown....