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Cell-Type Specific Posttranslational Processing of Peptides by Different Pituitary Cell Lines^*

IAN M. DICKERSON and RICHARD E MAINS

Department of Neuroscience, The Johns Hopkins University School of Medicine Baltimore, Maryland 21205

Address requests for reprints to: Dr. Richard E. Mains, Department of Neuroscience, WBSB 907, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, Maryland 21205.

Abstract

In order to compare prohormone processing in two distinct pituitary cell types, somatomammotrope cells (GH₃) and corticotrope cells (AtT-20) were stably transfected with vectors encoding preproneuropeptide Y (preproNPY) containing four different pairs of basic amino acids at the single endoproteolytic cleavage site: wildtype or KR (lysine-arginine), RR, RK, and KK. The GH-NPY cell lines cleaved proNPY to a similar extent, regardless of the sequence of the basic amino acids at the cleavage site (KR = RR = RK = KK). AtT-20-NPY cells are known to exhibit a strong hierarchy of cleavage site preference when processing wildtype and mutated proNPY forms (KR = RR > RK >> KK). All four types of GH-NPY and AtT-NPY cells faithfully produced NPY(1-36)NH₂ from proNPY (1-69), regardless of the amino acid sequence at the cleavage site. All four types of GH-NPY cells produced some of the expected proNPY-COOH-terminal peptide with Ser⁴⁰ at its NH₂-terminal [proNPY(40-69)]. GH₃ cells expressing the RR, RK, and KK forms of proNPY yielded in addition some proNPY-COOHterminal peptide retaining the amino terminals Lys³⁹ or Arg³⁹ residue. In contrast, AtT-NPY-RK cells produced only the Lys³⁹ form of proNPY-COOH-terminal peptide while the other three AtT-NPY lines (KR, RR, and KK) produced only the Ser⁴⁰ form of proNPY-COOH-terminal peptide. The residence time of proNPY and NPY in GH₃ cells was dramatically increased by treatment with insulin, estradiol, and epidermal growth factor, in concert with the expected increase in PRL synthesis and decrease in GH synthesis; increased residence time in the cells did not result in an increase in the extent of cleavage of proNPY to NPY. AtT-20 cells did not respond to the somatomammotrope- specific set of hormones. Thus, there are several important differences in the posttranslational processing and storage of peptide hormones in corticotropes and somatomammotropes (Endocrinology 127: 133–140,1990)

Footnotes

^* This work was supported by NIH Grants DK-32948, DA-00097, and DK-08121.

Current address: Department of Physiology and Biophysics, University of Miami School of Medicine, Miami Florida.

Received February 23, 1990.

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