Section 5
Chapter 4,536

2 distinct intra cellular pathways transport secretory and membrane glyco proteins to the surface of pituitary tumor cells

Gumbiner, B.; Kelly, R.B.

Cell 28(1): 51-60


ISSN/ISBN: 0092-8674
Accession: 004535459

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The pituitary cell line AtT-20 synthesizes ACTH as a glycoprotein precursor that is cleaved into mature hormones during packaging into secretory granules. The cells also produce an endogenous leukemia virus (MuLV) that is glycosylated after translation similar to the glycosylation of the ACTH precursor. The envelope glycoprotein and some precursor ACTH apparently get to the cell surface in a vesicle different from the mature ACTH secretory granule. Viral glycoproteins and ACTH precursor are released from the cells much sooner after synthesis than mature ACTH. Isolated secretory granules do not contain significant amounts of the envelope glycoprotein or ACTH precursor. Exposing cells to 8Br-cAMP stimulates release of mature ACTH 4- to 5-fold but has little effect on the release of the ACTH precursor or the viral glycoproteins. The viral glycoproteins and some of the ACTH precursor are probably transported by a constitutive pathway; mature ACTH is stored in secretory granules where its release is enhanced by stimulation.

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