Inhibitory effect of the alpha1-antitrypsin Pittsburgh type-mutant (alpha1-PIM/R) on proinsulin processing in the regulated secretory pathway of the pancreatic beta-cell line MIN6.
To elucidate its effect on proinsulin processing, we introduced the expression of a Pittsburgh type-mutant, alpha1-protease inhibitor M/R (alpha1-PIM/R) and its chimera protein with growth hormone (GH) (GHalpha1-PIM/R) into MIN6 cells. In metabolic labeling and chasing experiments with [3H]-Leu and [35S]-Met, proinsulin appeared in the medium during stimulatory secretion only from MIN6 clones expressing GHalpha1-PIM/R and, surprisingly, alpha1-PIM/R, but not from the clones of either the control or alpha1-PI. The major part of alpha1-PIM/R was secreted through the constitutive pathway and about 10% of total secreted alpha1-PIM/R in the chase periods entered the regulated pathway. On the other hand, GHalpha1-PIM/R was mainly transported to the secretory granules and about 80% of the total secreted GHalpha1-PIM/R in the chase periods was secreted during stimulatory secretion. In the first 3 h chase periods without stimulation, only alpha1-PIM/R and no GHalpha1-PIM/R appeared in the medium, thus suggesting that alpha1-PIM/R might be transported through a constitutive-like pathway for those periods. The alpha1-PI, which had no inhibitory effect on proinsulin processing, showed similar secretion pathways to those of alpha1-PIM/R. This implies that some part of alpha1-PIM/R and alpha1-PI entered the regulated pathway, not due to any specific interaction between the processing endoproteases and serine protease inhibitors, but due to some type of passive transport in a nonselective manner. The inhibitory effect of alpha1-PIM/R in the regulated secretory pathway was slightly but clearly evident when it was expressed in MIN6 beta-cells.
Department of Laboratory Medicine, Fukuoka University School of Medicine, Fukuoka 814-0180, Japan.
Kumiko
K
Ohkubo
Yuko
Y
Naito
Toshiyuki
T
Fujiwara
Jun-ichi
J
Miyazaki
Yukio
Y
Ikehara
Junko
J
Ono
D000818:Animals; D015152:Blotting, Northern; D045744:Cell Line, Tumor; D045683:Furin / Q000235:genetics; D013006:Growth Hormone / Q000235:genetics; D007150:Immunohistochemistry; D007340:Insulinoma; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism* / Q000502:physiology*; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D011384:Proinsulin / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D022142:Secretory Vesicles / Q000378:metabolism; D000515:alpha 1-Antitrypsin / Q000235:genetics* / Q000378:metabolism
D011993:Recombinant Fusion Proteins; D000515:alpha 1-Antitrypsin; D013006:Growth Hormone; D011384:Proinsulin; D045683:Furin