DEVELOPMENTAL AND HORMONAL-REGULATION OF UDP-GLCNAC-DOLICHOL PHOSPHATE GLCNAC-1-P TRANSFERASE IN MOUSE MAMMARY-GLAND

The developmental and hormonal regulation of UDP-GlcNAc:dolichol phosp hate N-acetylglucosamine-1-phosphate transferase (GPT), the enzyme whi ch initiates the biosynthesis of asparagine-linked glycoproteins, was investigated in mouse mammary glands. An anti-peptide antibody raised against the carboxyl-terminal 11 amino acids of mouse GPT, immunoadsor bed GPT activity and recognized a protein of expected size (similar to 48 kDa) on Western blots. Mouse mammary glands at different stages of development were examined for GPT activity, immunoreactive protein, a nd GPT mRNA. All three parameters showed a similar trend, i.e. they we re low in tissues from virgin and pregnant animals, increased steadily during lactation, reaching a peak around mid to late lactation, and d eclined thereafter in glands from post-lactating animals. At mid-lacta tion, the increase in GPT activity, immunoreactive protein, and GPT mR NA relative to the virgin stage was 9.5-, 3.3- and 5.4 fold respective ly, on a per cell basis. These data suggest possible transcriptional a nd post-transcriptional modulation of GPT gene expression during devel opment of mouse mammary gland. The results on hormonal regulation of G PT in mouse mammary explants and primary mouse mammary epithelial cell s showed that all three parameters cited above were stimulated maximal ly by the combined presence of insulin, hydrocortisone, and prolactin, indicating that the hormonal regulation of GPT expression is also med iated at the level of RNA.