ACCUMULATION OF GLUCOSAMINYL(ACYL)PHOSPHATIDYLINOSITOL IN AN S3 HELA SUBLINE EXPRESSING NORMAL DOLICHOLPHOSPHOMANNOSE SYNTHASE ACTIVITY

Glucosaminyl(acyl)phosphatidylinositol [GlcN(acyl)PI], the third inter mediate in the mammalian glycosylphosphatidylinositol (GPI) anchor pat hway, is undetectable in most cells. This intermediate was previously shown to accumulate, however, in murine lymphoma mutant E and in yeast mutant dpm1, both of which lack dolicholphosphomannose synthase activ ity. Here we report that a mammalian HeLa S3 subline, denoted D, produ ces large amounts of GlcN(acyl)PI. The level of GlcN(acyl)PI in this s ubline is twice that in the murine lymphoma mutant E and 4 times that in the parental S3 line. This HeLa D subline differs from the previous ly reported mutants that accumulate GlcN(acyl)PI because no defects in the synthesis or utilization of dolicholphosphomannose were found. Ki netic analysis indicated that in this HeLa subline there is an increas ed rate of synthesis of GlcN(acyl)PI, whereas the rate of metabolism f or this GPI is comparable to that in wild-type cells. Furthermore, HeL a D cells accumulate GlcN(acyl)PI without a block in the synthesis of the downstream mannosylated GPI anchor precursors and GPI-anchored pro teins. These findings might be relevant for understanding the regulati on of the GPI pathway.