PDZ Domain-mediated interaction of interleukin-16 precursor proteins with myosin phosphatase targeting subunits.
The cytokine interleukin-16 is generated by posttranscriptional cleavage by caspase-3 of two large precursor isoforms. The smaller protein of 67 kDa (pro-IL-16) is expressed in cells of the immune system and contains three PDZ (postsynaptic density/disc large/zona occludens-1) domains, whereas the larger 141-kDa neuronal variant (npro-IL-16) has two additional PDZ domains in its N-terminal extension that interact with neuronal ion channels. Using the yeast two-hybrid approach we have identified three closely related myosin phosphatase targeting subunits, MYPT1, MYPT2, and MBS85, as binding partners of the IL-16 precursor proteins. These interactions were verified using pull-down assays, coimmunoprecipitations, and plasmon resonance experiments. Binding requires the intact PDZ2 domain of pro-IL-16 and highly related C-terminal regions in the ligands consisting of a short leucine zipper and an indispensable serine at the -1 position, suggesting a novel unconventional PDZ binding mode. Pro-IL-16 and the myosin phosphatase targeting subunits colocalize along actomyosin filaments and stress fibers in transfected COS-7 cells. By modulating and targeting the catalytic phosphatase subunit to its substrates, MYPT1, MYPT2, and MBS85 regulate various contractile processes in muscle and non-muscle cells. Our findings indicate an involvement of the IL-16 precursor molecules in myosin-based contractile processes, most likely in cell motility, providing a functional link to the chemotactic activity of the mature cytokine. Alternatively, an intracellular complex of npro-IL-16, ion channels, and components of myosin motors in neurons suggests a role in protein targeting.
Bannert
Norbert
N
Robert Koch-Institute, Nordufer 20, 13353 Berlin, Germany. BannertN@rki.de
Vollhardt
Karin
K
Asomuddinov
Bakhtier
B
Haag
Marion
M
König
Herbert
H
Norley
Stephen
S
Kurth
Reinhard
R
D000205:Actomyosin / Q000378:metabolism; D000595:Amino Acid Sequence; D001665:Binding Sites; D006801:Humans; D019410:Interleukin-16 / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D007962:Leukocytes / Q000737:chemistry; D008024:Ligands; D008969:Molecular Sequence Data; D043263:Myosin-Light-Chain Phosphatase / Q000378:metabolism*; D011485:Protein Binding; D011498:Protein Precursors / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000302:isolation & purification / Q000378:metabolism*; D022502:Stress Fibers / Q000378:metabolism; D020798:Two-Hybrid System Techniques
D019410:Interleukin-16; D008024:Ligands; D011498:Protein Precursors; D021122:Protein Subunits; C105950:interleukin 16 precursor; D000205:Actomyosin; D043263:Myosin-Light-Chain Phosphatase