Preneoplastic and neoplastic liver nodules and hepatocytes isolated from regenerating rat liver have been shown to be resistant to a broad range of carcinogenic agents. This phenomenon was studied by measuring the expression of the multidrug-resistant (mdr) gene in normal liver cells and in preneoplastic and neoplastic nodules and regenerating liver. Levels of messenger RNA for the mdr gene, which encodes P-glycoprotein, were elevated in both preneoplastic and neoplastic lesions. Expression of the mdr gene also reached high levels in regenerating rat liver 24 to 72 hours after partial hepatectomy. These results show that the expression of the mdr gene can be regulated in liver and is likely to be responsible for part of the multidrug-resistance phenotype of carcinogen-initiated hepatocytes and regenerating liver cells.

The biosynthesis and maturation of glucocerebrosidase were studied in fibroblasts from patients with the neurological and non-neurological forms of Gaucher disease and in control cells. In control fibroblasts the precursor of glucocerebrosidase (62 -63 kDa), observed after a short pulse with [35S]methionine, was converted during the chase period to a 66-kDa intermediate form and, finally, to the 59-kDa mature protein. In fibroblasts from patients with the non-neurological phenotype of Gaucher disease (type 1) the same biosynthetic forms were seen as in control fibroblasts. These biosynthetic forms correspond to the three-banded pattern seen in control and Gaucher type 1 fibroblast extracts analysed by the immunoblotting procedure, or after electrophoresis and fluorography of extracts of such fibroblasts cultured for 5 days with [14C]leucine. The 59-kDa protein seen in type 1 fibroblasts was unstable and disappeared after a prolonged chase; this disappearance was not observed when the cells were grown in the presence of leupeptin. In fibroblasts from patients with the neurological forms of Gaucher disease (types 2 and 3) the 62.5-kDa precursor of glucocerebrosidase was present in near-normal amounts after a short pulse, but the 59-kDa form was not detected even when cells were cultured with leupeptin.

Multiple molecular forms of (3-glucocerebrosidase that permit discrimination between neurologic and non-neurologic phenotypes of Gaucher disease have been identified radioimmunologically in fibroblasts and human brain tissue. In normal human fibroblasts these forms have been shown by NaDodSO4/polyacrylamide gel electrophoresis to have apparent Mr of 63,000 (form A1), 61,000 (form A2), and 56,000 (form B). The Mr 63,000 form may be a precursor of the Mr 56,000 form. Nonneurologic Gaucher disease (type 1) fibroblasts and normal brain tissue are characteristic in that they contain only one major immunoreactive protein, the Mr 56,000 form. In contrast, fibroblast extracts and brain tissue from neurologic Gaucher disease phenotypes contain only the higher molecular weight forms A1 and A2. These data and the low residual activity of the enzyme in all the variants of Gaucher disease suggest that the mutations of fi-glucocerebrosidase are allelic and involve the active site. Fibroblast Culture and Preparation. Skin fibroblasts from normals and Gaucher disease patients were obtained from patient biopsies and from the Human Genetic Mutant Cell Repository. All fibroblasts were cultured to confluency in McCoy's 5A medium supplemented with 10% fetal calf serum and antibiotics. Cells were harvested by trypsinization and washed with culture medium and phosphate-buffered saline (P1/NaCl) at pH 7.2. Fibroblasts stci d in a 50% (vol/vol) mixture of Cryoprotective media (M.A. Bioproducts, Walkersville, MD) and McCoy's SA with 40% fetal calf serum were rapidly thawed at 370C and washed with P1/NaCl at pH 7.2.Fibroblast pellets were suspended in 60 mM potassium phosphate (pH 6.6) containing 0.1% Triton X-100 and were then sonicated at 40 W for 5 sec at 40C. The sonicates were centrifuged at 40C at 48,000 x g for 20 min and the supernatants were stored at -20'C. 5607The publication costs ofthis article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact.