Stepwise posttranslational processing of progrowth hormone-releasing hormone (proGHRH) polypeptide by furin and PC1.
Through a posttranslational processing mechanism, pro-growth hormone releasing hormone (proGHRH) gives rise to an amidated GHRH molecule, which in turn stimulates the synthesis and release of growth hormone. We have previously proposed a model for the biochemical processing of proGHRH [Nillni et al. (1999), Endocrinology 140, 5817-5827]. We demonstrated that the proGHRH peptide (10.5 kDa, 104 aa) is first processed to an 8.8 kDa intermediate form that is later cleaved to yield two products: the 5.2 kDa GHRH and the 3.6 kDa GHRH-RP. However, the proteolytic enzymes involved in this process are unknown. Therefore, in this study we determined which proconverting enzymes are involved in this process. We transfected different constructs in cell lines carrying different PC enzymes followed by analysis of the peptide products after metabolic labeling or Western blots. We found that in the absence of furin (LoVo cells) or CHO cells treated with BFA, only one moiety was observed, and that corresponds to the same electrophorectic mobility to the GHRH precursor. This finding strongly supports an initial role for furin in the processing of proGHRH. The results from transfections with preproGHRH alone or double or triple transfections with PC1 and PC2 in AtT-20, GH3, and GH4C1 cells indicated that PC1 is the primary enzyme involved in the generation of GHRH peptide from the 8.8 kDa intermediate form. We found that AtT-20 cells (high PC1, very low PC2) were able to generate GHRH. However, GH3 cells (high PC2, but not PC1) were able to process the 8.8 kDa peptide to GHRH only after the cotransfection with the PC1 enzyme. Transfections with preproGHRH-GFP and preproGHRH-V5 provided similar results in all the cell lines analyzed. These data support the hypothesis that proGHRH is initially cleave by furin at preproGHRH29-30, followed by a second cleavage at preproGHRH74 primarily by PC1 to generate GHRH and GHRH-RP peptides, respectively.
Posner
Samuel F
SF
Division of Endocrinology, Department of Medicine, Brown Medical School, Rhode Island Hospital, Providence, Rhode Island 02903, USA.
Vaslet
Charles A
CA
Jurofcik
Michelle
M
Lee
Alisson
A
Seidah
Nabil G
NG
Nillni
Eduardo A
EA
D000818:Animals; D015153:Blotting, Western; D016466:CHO Cells; D002478:Cells, Cultured; D006224:Cricetinae; D005260:Female; D045683:Furin / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D013007:Growth Hormone-Releasing Hormone / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D007031:Hypothalamus / Q000166:cytology / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics; D009474:Neurons / Q000378:metabolism; D045664:Proprotein Convertase 1 / Q000378:metabolism*; D045706:Proprotein Convertase 2 / Q000378:metabolism; D011498:Protein Precursors / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014018:Tissue Distribution
D008164:Luminescent Proteins; D011498:Protein Precursors; D011993:Recombinant Fusion Proteins; C099166:growth hormone releasing hormone-related peptide; C047524:pre-pro-growth hormone releasing factor; D049452:Green Fluorescent Proteins; D013007:Growth Hormone-Releasing Hormone; D045683:Furin; D045664:Proprotein Convertase 1; D045706:Proprotein Convertase 2