Fibronectin expression in human mesangial cell cultures and its alterations by adriamycin

Human mesangial cell (HMC) cultures synthesize cellular fibronectin (FN), which is secreted and incorporated into a fibrillar extracellular matrix (ECM). The anticancer drug adriamycin (ADR) induces changes in extracellular FN deposition. As revealed by immunofluorescence staining, a 24 h incubation of the cells with 2 micrograms ADR/ml resulted in a marked expansion of the pericellular FN fibers, which may be due to either an increased synthesis or a decreased FN degradation. The effects of ADR on FN mRNA were analysed by northern hybridization and in vitro translation. Steady-state FN mRNA levels were significantly increased by 60% following ADR administration. However, yields of radioactivity incorporated into FN by cell-free translation remained constant (2.3 +/- 0.7%, n = 24, vs controls 2.2 +/- 0.8% of total radioactivity, n = 23). The quality of translation products was not affected by the drug, whereas translation efficiency of total RNA from ADR-treated HMC was only 75% of controls. The data presented suggest a negative feedback control of FN expression on the level of translation. Extracellular FN accumulation in the experimental model of ADR-induced progressive glomerulopathy therefore cannot be explained by an increased FN synthesis, but is rather regarded a consequence of proteinase inhibition. This assumption is compatible with a diminished number of FN fragments recently demonstrated in the culture medium of ADR-treated HMC, and is further corroborated by the loss of urinary FN degradation products accompanying the onset of proteinuria in ADR-treated rats.