precursors, human diploid fibroblasts no longer exhibited density-dependent inhibition of growth. Concomitantly, increased 2. Materials and methods sialylation of contaetinhibin, a glycoprotein involved in densitydependent inhibition of growth, was observed. These results Cell culture indicate that sialidase-resistant sialic acid modifications lead toHuman diploid lung fibroblasts were cultured as described earlier dysregulated growth control. The modifications have been [11] with the modifcation that CG-medium (Vitromex, Vilshofen, induced by N-propanoyl and other N-acyl derivatives of DGermany) was used at 0.5% FCS (Roth, Karlsrube, Germany) instead mannosamine, of DMEM at 10% FCS. Isolation of intracellular and plasma membrane localized