Endocytosis and intracellular protein degradation in cystic fibrosis fibroblasts

Accelerated endocytosis and incomplete catabolism of radical-damaged protein

Native bovine serum albumin (BSA) was endocytosed and degraded at a steady rate by resident peritoneal murine macrophages with barely detectable amounts remaining within the cells. Radical-damaged BSA was endocytosed and degraded up to 2.5-fold more rapidly than native BSA, but some radical-damaged BSA accumulated within the cells in a time-dependent manner. The extent of accumulation increased in parallel with that of radical damage. Thus, some radical-damaged BSA was processed less efficiently than native BSA. Such inefficient catabolism of radical-damaged proteins may contribute to certain diseases such as atherosclerosis.

Use of cultured human cells for biochemical analysis

The use of cultured human cells for biochemical analysis is increasing. This reflects the many advantages of such cells over tissue samples: independence of the measurements from the biological milieu of the donor, better control of experimental variables and the possibility of immortalizing the patient via his cells. Concomitant with these advantages, however, are certain new experimental variables which, if not properly controlled, can yield spurious results. This paper describes the types of cultured human cells that are generally available and the basic steps involved in their culture, as well as a discussion of the sources of variability in biochemical measurements which can be attributed to cell culture.

Proteolytic capacities of cystic fibrosis and control fibroblasts towards Tamm-Horsfall glycoprotein

125I-labelled Tamm-Horsfall glycoprotein was incubated at pH 5.0 and pH 7.4 with homogenates of cultured fibroblasts from cystic fibrosis patients and controls in order to compare the total proteolytic capacities of these cells. No significant breakdown could be observed at pH 7.4. Protein degradation at pH 5.0 occurred at comparable rates in cells from patients and controls, with the possible exception of one cystic fibrosis line. Therefore, a decreased proteolytic capacity cannot be a general cellular characteristic of cystic fibrosis. Though occurrence of heterogeneity cannot be excluded, the exception probably represents just random variation.