Signaling from the secretory granule to the nucleus: Uhmk1 and PAM.
Neurons and endocrine cells package peptides in secretory granules (large dense-core vesicles) for storage and stimulated release. Studies of peptidylglycine alpha-amidating monooxygenase (PAM), an essential secretory granule membrane enzyme, revealed a pathway that can relay information from secretory granules to the nucleus, resulting in alterations in gene expression. The cytosolic domain (CD) of PAM, a type 1 membrane enzyme essential for the production of amidated peptides, is basally phosphorylated by U2AF homology motif kinase 1 (Uhmk1) and other Ser/Thr kinases. Proopiomelanocortin processing in AtT-20 corticotrope tumor cells was increased when Uhmk1 expression was reduced. Uhmk1 was concentrated in the nucleus, but cycled rapidly between nucleus and cytosol. Endoproteolytic cleavage of PAM releases a soluble CD fragment that localizes to the nucleus. Localization of PAM-CD to the nucleus was decreased when PAM-CD with phosphomimetic mutations was examined and when active Uhmk1 was simultaneously overexpressed. Membrane-tethering Uhmk1 did not eliminate its ability to exclude PAM-CD from the nucleus, suggesting that cytosolic Uhmk1 could cause this response. Microarray analysis demonstrated the ability of PAM to increase expression of a small subset of genes, including aquaporin 1 (Aqp1) in AtT-20 cells. Aqp1 mRNA levels were higher in wild-type mice than in mice heterozygous for PAM, indicating that a similar relationship occurs in vivo. Expression of PAM-CD also increased Aqp1 levels whereas expression of Uhmk1 diminished Aqp1 expression. The outlines of a pathway that ties secretory granule metabolism to the transcriptome are thus apparent.
Francone
Victor P
VP
Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut 06032, USA.
Ifrim
Marius F
MF
Rajagopal
Chitra
C
Leddy
Christopher J
CJ
Wang
Yanping
Y
Carson
John H
JH
Mains
Richard E
RE
Eipper
Betty A
BA
D000818:Animals; D051398:Aquaporin 1 / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D005434:Flow Cytometry; D036681:Fluorescence Recovery After Photobleaching; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008856:Microscopy, Fluorescence; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D016133:Polymerase Chain Reaction; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D053481:Secretory Leukocyte Peptidase Inhibitor / Q000235:genetics / Q000378:metabolism; D022142:Secretory Vesicles / Q000378:metabolism*
D047908:Intracellular Signaling Peptides and Proteins; D009097:Multienzyme Complexes; D053481:Secretory Leukocyte Peptidase Inhibitor; D051398:Aquaporin 1; D006899:Mixed Function Oxygenases; C035189:peptidylglycine monooxygenase; D017346:Protein Serine-Threonine Kinases; C530659:Uhmk1 protein, mouse