Synthesis and glycosylation of the common alpha subunit of human glycoprotein hormones in mouse cells.

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Abstract
The synthesis and the post-translational modification of the .alpha. subunit of human glycoprotein hormones [thyrotropin, lutropin, follitropin and chorionic gonadotropin] were studied in a mouse cell. A full-length cDNA coding for the human .alpha. subunit was expressed in mouse C127 cells under the control of mouse metallothionein regulatory sequences, using a bovine papilloma virus vector. Stable clones secreting the .alpha. subunit into the medium were obtained. Two intracellular forms of 22,000 Da and 21,000 Da were detected. Pulse-chase experiments suggest that the 22,000-Da form is exported, while the 21,000-Da form appears to remain intracellular. The secreted form of the .alpha. subunit migrates as a broad peak between 22,000 and 30,000 Da, suggesting further modification of the intracellular form prior to secretion. Both the secreted and the intracellular forms incorporate glucosmine label, indicating that at least a portion of the modification observed here is in the form of glycosylation.