Characterization of spherical amyloid protein from a prolactin-producing pituitary adenoma.
Prolactin (PRL)-producing pituitary adenomas are in some cases associated with deposition of abundant spherical amyloid; however, the origin of the amyloid has not been established. In this report, a PRL-producing pituitary adenoma composed almost entirely of spherical amyloid was analyzed biochemically. The tumor was removed surgically from a 56-year-old man. Immunohistochemical analysis revealed that residual tumor cells were strongly positive for PRL, while the spherical amyloid was not. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a band of approximately 4 kDa associated with the amyloid, which was not present in a nonamyloid producing prolactinoma. The 4-kDa band is similar in size to other known amyloidogenic peptides. Immunoblot analysis of the tumor material using polyclonal anti-human PRL antibodies revealed a small amount of normal-sized PRL; however, the abundant 4-kDa band was nonimmunoreactive. Amino acid sequencing showed that this peptide represents the first 34 amino acids of the intact PRL protein with a predicted size of 4313 Da. The presence of a small amount of normal-sized PRL in this tumor, as well as elevated circulating levels of PRL implies that intact PRL is being abnormally processed in the formation of spherical amyloid.
Hinton
D R
DR
Department of Pathology, University of Southern California School of Medicine, Los Angeles 90033, USA.
Polk
R K
RK
Linse
K D
KD
Weiss
M H
MH
Kovacs
K
K
Garner
J A
JA
D000595:Amino Acid Sequence; D000682:Amyloid / Q000032:analysis* / Q000648:ultrastructure; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D015151:Immunoblotting; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D010911:Pituitary Neoplasms / Q000737:chemistry* / Q000648:ultrastructure; D011388:Prolactin / Q000096:biosynthesis*; D015175:Prolactinoma / Q000737:chemistry* / Q000648:ultrastructure
D000682:Amyloid; D011388:Prolactin