© The Rockefeller University Press,
0021-9525/1998//803 $5.00
The Journal of Cell Biology, Volume 142, Number 3,
, 1998 803-813
Regulation of Organelle Movement in Melanophores by Protein Kinase A (PKA), Protein Kinase C (PKC), and Protein Phosphatase 2A (PP2A)
Amy R. Reilein*,
Irina S. Tint*,
Natalia I. Peunova
,
Grigori N. Enikolopov, and
Vladimir I. Gelfand*
* Department of Cell and Structural Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 and Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724
We used melanophores, cells specialized for regulated organelle transport, to study signaling pathways involved in the regulation of transport. We transfected immortalized Xenopus melanophores with plasmids encoding epitope-tagged inhibitors of protein phosphatases and protein kinases or control plasmids encoding inactive analogues of these inhibitors. Expression of a recombinant inhibitor of protein kinase A (PKA) results in spontaneous pigment aggregation. 
-Melanocyte-stimulating hormone (MSH), a stimulus which increases intracellular cAMP, cannot disperse pigment in these cells. However, melanosomes in these cells can be partially dispersed by PMA, an activator of protein kinase C (PKC). When a recombinant inhibitor of PKC is expressed in melanophores, PMA-induced pigment dispersion is inhibited, but not dispersion induced by MSH. We conclude that PKA and PKC activate two different pathways for melanosome dispersion. When melanophores express the small t antigen of SV-40 virus, a specific inhibitor of protein phosphatase 2A (PP2A), aggregation is completely prevented. Conversely, overexpression of PP2A inhibits pigment dispersion by MSH. Inhibitors of protein phosphatase 1 and protein phosphatase 2B (PP2B) do not affect pigment movement. Therefore, melanosome aggregation is mediated by PP2A.
Key Words: microtubules • protein phosphorylation • microtubule motors • kinesin II • cytoplasmic dynein
Abbreviations used in this paper: CaMK, Ca2+/calmodulin-dependent kinase; CREB, cAMP-response element binding protein; GFP, green fluorescent protein; HA, hemagglutinin; IBMX, 3-isobutyl-1-methyl xanthine; MSH, melanocyte-stimulating hormone; PKA, protein kinase A; PKC, protein kinase C; PP1, protein phosphatase 1; PP2A, protein phosphatase 2A; PP2B, protein phosphatase 2B.
Address all correspondence to Vladimir Gelfand, University of Illinois, Department of Cell and Structural Biology, B107 Chemical and Life Sciences Laboratory, 601 South Goodwin Ave., Urbana, IL 61801. Tel.: (217) 333-5972. Fax: (217) 333-5982. E-mail: vgelfand{at}uiuc.edu
I.S. Tint's present address is Department of Anatomy and Cell Biology, Temple University School of Medicine, Philadelphia, PA 19140.
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